Heredity and Evolution

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CBSE Learning Objectives – Key Concepts & Skills You Must Know

Understand the concept of trait inheritance in asexually reproducing species.
Analyze the relationship between trait prevalence and its historical emergence in a population.
Explain how variations within a species contribute to survival and adaptation.
Describe the process of sex determination in humans, including the roles of male and female gametes.
Interpret Punnett squares to predict genotypes and phenotypes of offspring from genetic crosses.
Apply Mendelian genetics principles to understand inheritance patterns of traits.

CBSE Revision Notes & Quick Summary for Last-Minute Study

Chapter 8: Heredity

8.1 Accumulation of Variation During Reproduction

Reproductive processes lead to new individuals that are similar but different.
Asexual reproduction results in minimal variation, while sexual reproduction maximizes variation.
Example: In a field of sugarcane, individual plants show little variation compared to sexually reproducing animals like humans.

8.2 Heredity

The rules of heredity determine how traits and characteristics are inherited.
Inherited Traits: Children inherit basic features from parents but also show variation.
Mendel's Contributions:
- Traits can be dominant or recessive.
- Each trait is influenced by both paternal and maternal DNA.

8.2.1 Inherited Traits

Example Activity: Observe earlobes in a class to determine inheritance patterns.

8.2.2 Rules for the Inheritance of Traits

Mendel's Experiments:
- Parental Generation (P): Tall (TT) × Short (tt) plants.
- Resulting Offspring (F1): All Tall (Tt).
- F1 Cross: Tall (Tt) × Tall (Tt) results in Tall (TT, Tt) and Short (tt) offspring.

Sex Determination in Humans

Male: XY chromosomes; Female: XX chromosomes.
Male gametes: X and Y; Female gamete: X.
Zygote formation:
- XX (female offspring) or XY (male offspring).

Important Diagrams

Figure 8.6: Sex determination in humans.
- Male (XY) and Female (XX) representation.
- Gametes and zygote formation illustrated.

CBSE Exam Tips, Important Questions & Common Mistakes to Avoid

Common Mistakes and Exam Tips

Common Pitfalls

Misunderstanding Dominance: Students often confuse dominant and recessive traits. For example, in Mendel's experiments, the tall trait (T) is dominant over the short trait (t). Ensure you understand which traits are dominant and which are recessive.
Assuming Equal Contribution: It's a common mistake to think that traits are inherited equally from both parents without considering dominant and recessive traits. Remember that dominant traits can mask the presence of recessive traits in the phenotype.
Ignoring Independent Assortment: Students may overlook that traits can be inherited independently. For example, in Mendel's experiments, seed shape and color are inherited independently, leading to new combinations in the offspring.
Confusing Genotypes and Phenotypes: Be clear about the difference between genotype (the genetic makeup) and phenotype (the observable traits). For instance, both TT and Tt genotypes result in a tall phenotype.

Exam Tips

Review Mendel's Experiments: Familiarize yourself with Mendel's experiments and the conclusions he drew about dominant and recessive traits, as well as independent assortment.
Practice Punnett Squares: Use Punnett squares to predict the outcomes of genetic crosses. This will help you visualize how traits are inherited and the ratios of different genotypes and phenotypes.
Understand Sex Determination: Be clear on how sex is determined in humans, specifically the role of X and Y chromosomes. Remember that the male contributes either an X or a Y chromosome, while the female contributes an X chromosome.
Clarify Inheritance Patterns: Make sure to understand the inheritance patterns of traits, including how traits can be linked or independently assorted, as demonstrated in Mendelian genetics.

CBSE Quiz & Practice Test – MCQs, True/False Questions with Solutions

Multiple Choice Questions

1/16

3/16

1/4

9/16

Correct Answer: A

Solution:

The probability of getting white flowers (rr) is 1/4 and the probability of getting narrow leaves (bb) is also 1/4. Therefore, the probability of getting both white flowers and narrow leaves is (1/4) * (1/4) = 1/16.

Mendel studied the inheritance of traits in animals.

Mendel's experiments showed that traits are inherited independently.

Mendel discovered the structure of DNA.

Mendel's work was immediately recognized and celebrated.

Correct Answer: B

Solution:

Mendel's experiments demonstrated that traits are inherited independently, which is one of his key contributions to genetics.

To ensure diversity

To maintain stability of species DNA

To increase the rate of reproduction

To allow for mutations

Correct Answer: B

Solution:

Having two copies of genes helps maintain the stability of species DNA during reproduction.

1/4

1/2

3/4

1/8

Correct Answer: B

Solution:

The possible genotypes from the cross are Ss and ss. The probability of getting smooth seeds (Ss) is 1/2.

1:1

3:1

1:2

2:1

Correct Answer: B

Solution:

Using a Punnett square, the possible genotypes for the offspring are FF, Ff, Ff, and ff. The phenotypic ratio of fanned fins (FF and Ff) to straight fins (ff) is 3:1.

0.00

0.25

0.50

0.75

Correct Answer: C

Solution:

The cross Ll (long tail) with ll (short tail) results in possible genotypes of Ll and ll. The probability of an offspring having a short tail (ll) is 1 out of 2, or 0.50.

Traits are inherited as a blend of both parents' traits.

Traits are inherited independently of each other.

Only maternal traits are inherited.

Traits are inherited only if they are dominant.

Correct Answer: B

Solution:

Mendel's experiments showed that traits are inherited independently, as demonstrated by the independent assortment of different traits.

Shortness

Wrinkled seeds

Tallness

White flowers

Correct Answer: C

Solution:

Tallness is a dominant trait in pea plants as demonstrated by Mendel's experiments.

All offspring were tall.

All offspring were short.

Offspring were a mix of tall and short plants.

Offspring were medium height.

Correct Answer: C

Solution:

When tall pea plants (Tt) were self-pollinated, the offspring were a mix of tall (TT, Tt) and short (tt) plants.

25%

50%

75%

100%

Correct Answer: B

Solution:

The cross Ll x ll results in the genotypes Ll, Ll, ll, and ll. Thus, 50% of the offspring will have short fins (ll).

1/4

1/2

1/8

3/8

Correct Answer: B

Solution:

The probability of getting short beak (ll) is 1/2 and the probability of getting green feathers (bb) is 1/2. Therefore, the probability of getting both short beak and green feathers is (1/2) * (1/2) = 1/2.

It produces identical offspring.

It involves only one parent.

It combines genetic material from two parents.

It reduces the number of chromosomes.

Correct Answer: C

Solution:

Sexual reproduction contributes to genetic variation by combining genetic material from two parents, leading to offspring with unique genetic combinations.

All offspring were short with wrinkled seeds.

All offspring were tall with round seeds.

Offspring showed a mix of traits, including new combinations.

Offspring were identical to one of the parent plants.

Correct Answer: B

Solution:

The F1 generation from this cross were all tall with round seeds, indicating these traits are dominant.

1/16

3/16

1/4

9/16

Correct Answer: A

Solution:

The cross RrSs x RrSs yields the following combinations for white and wrinkled: rrss. The probability of white (rr) is 1/4 and wrinkled (ss) is 1/4. Thus, the probability of a plant with white flowers and wrinkled seeds is (1/4) * (1/4) = 1/16.

They have no impact on survival.

They select variants that are best suited for survival.

They cause mutations in the species.

They ensure all variations survive equally.

Correct Answer: B

Solution:

Environmental factors select variants that are best suited for survival, forming the basis for evolutionary processes.

1/16

3/16

1/4

1/8

Correct Answer: D

Solution:

The cross can be represented as TtRr x ttrr. The probability of getting a tall plant (T_) is 1/2 and the probability of getting wrinkled seeds (rr) is 1/2. Therefore, the probability of getting a tall plant with wrinkled seeds is

1/2 \times 1/2 = 1/4

Only the maternal DNA

Only the paternal DNA

A combination of both maternal and paternal DNA

Random selection of traits

Correct Answer: C

Solution:

In sexually reproducing organisms, traits are influenced by a combination of both maternal and paternal DNA.

1/4

1/2

3/4

1/3

Correct Answer: A

Solution:

The cross Bb x Bb results in the following genotypes: BB, Bb, Bb, and bb. Only bb results in green scales. Thus, the probability of green-scaled offspring is 1/4.

0.60

0.63

0.65

0.70

Correct Answer: B

Solution:

The probability that an insect does not have the mutation is 0.95. The probability that none of the 10 insects have the mutation is

0.95^{10} = 0.5987

. Thus, the correct probability is approximately 0.63.

Trait A

Trait B

Both traits arose simultaneously

Cannot be determined

Correct Answer: B

Solution:

In an asexually reproducing population, a trait that exists in a larger percentage of the population is likely to have arisen earlier because it has had more time to spread through the population.

Mutations during DNA replication

Environmental changes

Recombination during sexual reproduction

Random mating

Correct Answer: C

Solution:

Recombination during sexual reproduction is the primary source of genetic variation.

1/4

1/2

3/4

1/3

Correct Answer: A

Solution:

The cross Dd x Dd results in the following genotypes: DD, Dd, Dd, and dd. Only dd results in striped wings. Thus, the probability of striped-winged offspring is 1/4.

1/4

1/8

1/2

1/16

Correct Answer: A

Solution:

The cross AaBb x aabb can produce gametes Ab, ab, aB, and ab. The probability of getting Aabb is

\frac{1}{2} \times \frac{1}{2} = \frac{1}{4}

RR and rr

Correct Answer: B

Solution:

When a round-flowered plant (RR) is crossed with an oval-flowered plant (rr), all offspring in the F1 generation will inherit one allele from each parent, resulting in the genotype Rr, which expresses the dominant round trait.

Random mutations.

Environmental changes.

Inheritance of a single gene set from each parent.

Inheritance of two gene sets from each parent.

Correct Answer: C

Solution:

The stability of DNA is ensured by the inheritance of a single gene set from each parent during sexual reproduction.

Only A

Only O

A or O

A, B, or O

Correct Answer: C

Solution:

A woman with blood group O has genotype ii, and a man with blood group A could have genotype IAIA or IAi. Their children could inherit either the IA or i allele from the father and the i allele from the mother, resulting in either blood group A (IAi) or O (ii).

1:1

3:1

1:2:1

All tall

Correct Answer: A

Solution:

The expected ratio is 1:1, with half the plants being tall (Tt) and half being short (tt).

Traits are only inherited from the mother.

Traits are inherited equally from both parents.

Traits are only inherited from the father.

Traits are inherited randomly from either parent.

Correct Answer: B

Solution:

Both the father and the mother contribute practically equal amounts of genetic material to the child.

All plants were tall.

All plants were short.

Three-quarters were tall, and one-quarter were short.

Half were tall, and half were short.

Correct Answer: C

Solution:

Mendel observed that the F2 generation consisted of three-quarters tall and one-quarter short plants, indicating the presence of recessive traits.

0.25

0.50

0.75

1.00

Correct Answer: A

Solution:

Using a Punnett square, the possible genotypes for the offspring are BB, Bb, Bb, and bb. Only the bb genotype results in brown feathers. Thus, the probability is 1 out of 4, or 0.25.

The mother's chromosomes

The father's chromosomes

Environmental factors

The child's diet

Correct Answer: B

Solution:

The sex of a child is determined by the father's chromosomes. An X chromosome results in a girl, and a Y chromosome results in a boy.

Traits are inherited as blended mixtures of parental traits.

Traits are inherited independently and can be dominant or recessive.

Only dominant traits are inherited.

Recessive traits are always expressed in the offspring.

Correct Answer: B

Solution:

Mendel's laws state that traits are inherited independently and can be dominant or recessive, as demonstrated by his experiments with pea plants.

3 red : 1 brown

1 red : 1 brown

1 red : 3 brown

All red

Correct Answer: A

Solution:

A cross between two heterozygous birds (Rr) will result in the following genotypic ratio: 1 RR : 2 Rr : 1 rr. The phenotypic ratio, considering red is dominant, will be 3 red : 1 brown.

0.6723

0.3277

0.4096

0.5904

Correct Answer: A

Solution:

The probability that a single bacterium does not have the mutation is 0.8. Therefore, the probability that none of the 5 bacteria have the mutation is

0.8^5 = 0.32768

. Thus, the probability that at least one has the mutation is

1 - 0.32768 = 0.67232

Bacteria that can withstand heat

Bacteria with no heat resistance

Bacteria that reproduce slowly

Bacteria with a high mutation rate

Correct Answer: A

Solution:

Bacteria that can withstand heat are more likely to survive a heat wave due to their advantageous trait.

A, B, AB, O

A, B, AB

B, AB, O

A, AB, O

Correct Answer: B

Solution:

The man (AB) can pass on either A or B alleles, while the woman (BO) can pass on either B or O alleles. The possible combinations are: AB, BB, AO, BO, leading to blood groups A, B, and AB.

Trait A

Trait B

Both traits arose simultaneously

Cannot be determined

Correct Answer: B

Solution:

Trait B is more prevalent in the population, suggesting it has been present for a longer time and has had more opportunities to spread.

A and B

A, B, and AB

A, B, AB, and O

Only AB

Correct Answer: A

Solution:

The man's genotype is IAIB and the woman's genotype is ii. The possible genotypes of their children are IAi (blood group A) and IBi (blood group B).

1:1

3:1

9:3:3:1

1:2:1

Correct Answer: C

Solution:

When crossing plants with two different traits, Mendel observed a 9:3:3:1 ratio in the F2 generation, indicating independent assortment of traits.

3/16

9/16

1/16

1/4

Correct Answer: A

Solution:

The genotype GgRr can produce gametes GR, Gr, gR, and gr. Using a Punnett square, the probability of yellow leaves (gg) is 1/4 and the probability of round flowers (R_) is 3/4. The combined probability is 1/4 * 3/4 = 3/16.

1/16

3/16

9/16

1/4

Correct Answer: A

Solution:

The genotype TtSs when self-pollinated will follow a dihybrid cross. The probability of short stems (tt) is 1/4 and rough leaves (ss) is 1/4. Therefore, the probability of both traits occurring together is 1/4 * 1/4 = 1/16.

Environmental factors

DNA copying inaccuracies

Mutations from radiation

Cross-breeding

Correct Answer: B

Solution:

In asexual reproduction, variations arise mainly due to small inaccuracies in DNA copying.

DNA directly forms traits without any intermediates.

DNA provides the information to make proteins, which influence traits.

DNA is only involved in the reproduction process.

DNA determines traits by altering environmental factors.

Correct Answer: B

Solution:

DNA contains the instructions for making proteins, which in turn influence the traits of an organism by affecting processes such as hormone production.

0.6723

0.3277

0.2000

0.8000

Correct Answer: A

Solution:

The probability that a single bacterium does not have the mutation is 0.8. The probability that none of the 5 bacteria have the mutation is 0.8^5 = 0.32768. Therefore, the probability that at least one has the mutation is 1 - 0.32768 = 0.67232.

25%

50%

75%

100%

Correct Answer: B

Solution:

The cross Rr x rr will produce offspring with genotypes Rr and rr. The probability of an offspring having oval seeds (rr) is 50%.

0.45

0.52

0.59

0.68

Correct Answer: C

Solution:

The probability that a plant does not have the mutation is 0.85. The probability that none of the 4 plants have the mutation is

0.85^4 = 0.522

. Thus, the probability that at least one plant has the mutation is

1 - 0.522 = 0.478

. Therefore, the correct probability is 0.59.

1:1

3:1

1:2:1

2:1

Correct Answer: B

Solution:

The cross Bb x Bb results in the genotypes BB, Bb, Bb, and bb. The phenotypic ratio is 3 blue (BB or Bb) to 1 white (bb).

1/4

1/2

3/4

1/8

Correct Answer: A

Solution:

The probability of getting yellow leaves (gg) is 1/4, as the possible genotypes from the cross are GG, Gg, Gg, and gg.

1:1

3:1

1:2:1

2:2

Correct Answer: B

Solution:

The F2 generation shows a 3:1 phenotypic ratio of tall to short plants.

0.6723

0.3277

0.4096

0.5904

Correct Answer: A

Solution:

1:1

3:1

1:2:1

2:1

Correct Answer: B

Solution:

The cross Rr x Rr results in the following genotypic ratio: 1 RR : 2 Rr : 1 rr. Since both RR and Rr result in red flowers, the phenotypic ratio is 3 red : 1 white.

Traits are inherited as blended mixtures from parents.

Traits are inherited independently and can be dominant or recessive.

Traits are inherited only from the mother.

Traits are inherited only if both parents exhibit them.

Correct Answer: B

Solution:

Mendel concluded that traits are inherited independently of each other and that each trait can be dominant or recessive. This means that the expression of one trait does not affect the expression of another, and dominant traits can mask the presence of recessive traits.

1/16

3/16

1/4

9/16

Correct Answer: A

Solution:

The genotype TtRr can produce gametes TR, Tr, tR, and tr. The probability of obtaining a short plant (tt) is 1/4, and the probability of obtaining wrinkled seeds (rr) is also 1/4. Therefore, the probability of obtaining a short plant with wrinkled seeds is (1/4) * (1/4) = 1/16.

1/4

1/2

3/4

1/8

Correct Answer: A

Solution:

The cross Bb x Bb results in the following genotypic ratio: 1 BB : 2 Bb : 1 bb. Therefore, the probability of having homozygous recessive (bb) offspring is 1/4.

30%

49%

76%

91%

Correct Answer: C

Solution:

The probability that a single bacterium does not have the mutation is 70%. Therefore, the probability that none of the 4 bacteria have the mutation is 0.7^4 = 0.2401. Thus, the probability that at least one has the mutation is 1 - 0.2401 = 0.7599, or approximately 76%.

25%

50%

75%

100%

Correct Answer: B

Solution:

The cross Ss x ss will produce offspring with genotypes Ss and ss. The probability of an offspring having spotted scales (ss) is 50%.

1/4

1/2

3/4

1/8

Correct Answer: A

Solution:

The probability of an offspring having spotted fur (ss) from a cross between two heterozygous striped-furred animals (Ss) is determined using a Punnett square. The possible genotypes are SS, Ss, Ss, and ss. Only ss results in spotted fur, giving a probability of 1/4.

1/4

1/2

3/4

1/8

Correct Answer: A

Solution:

The cross Rr x Rr results in the genotypes RR, Rr, Rr, and rr. Only the rr genotype results in white seeds, so the probability is 1/4.

All plants were short.

All plants were tall.

Half of the plants were tall, and half were short.

There were no plants in the F1 generation.

Correct Answer: B

Solution:

In the F1 generation, all plants were tall, indicating that the tall trait was dominant.

TTWW

TTww

TtWW

TtWw

Correct Answer: C

Solution:

The progeny all had violet flowers, indicating that violet is a dominant trait. Since half of the progeny were short, the tall parent must have been heterozygous for height, making the genetic makeup TtWW.

Tallness and round seeds are dominant traits.

Tallness and wrinkled seeds are dominant traits.

Shortness and round seeds are dominant traits.

Shortness and wrinkled seeds are dominant traits.

Correct Answer: A

Solution:

The F1 progeny all exhibit tallness and round seeds, indicating these traits are dominant.

The mother's chromosomes

The father's chromosomes

Environmental factors

Random chance

Correct Answer: B

Solution:

The sex of the child is determined by the father's chromosomes. A child who inherits an X chromosome from the father will be a girl, and one who inherits a Y chromosome will be a boy.

The size of the organism

The environmental conditions

The speed of reproduction

The number of offspring produced

Correct Answer: B

Solution:

Variations that provide an advantage in specific environmental conditions are more likely to survive.

All tall with round seeds

All short with wrinkled seeds

Tall with wrinkled seeds

Short with round seeds

Correct Answer: A

Solution:

In Mendel's experiments, the F1 generation showed dominant traits. Since tallness and round seeds are dominant, all F1 progeny will be tall with round seeds.

1:1

3:1

2:1

1:2:1

Correct Answer: B

Solution:

The cross Tt × Tt results in a 3:1 ratio of tall (TT, Tt) to short (tt) plants.

Genes are inherited as pairs, one from each parent.

Genes for different traits are inherited independently of each other.

Dominant genes mask the presence of recessive genes.

All traits are inherited as a single unit.

Correct Answer: B

Solution:

The law of independent assortment states that genes for different traits are inherited independently of each other, which Mendel demonstrated through dihybrid crosses.

1:1

2:1

3:1

4:1

Correct Answer: C

Solution:

Mendel observed a 3:1 ratio of tall to short plants in the F2 generation.

1/16

1/4

1/2

3/8

Correct Answer: B

Solution:

The probability of obtaining an offspring with narrow wings (ww) and yellow beak (rr) is calculated by considering each trait separately. The probability of narrow wings (ww) from Ww x ww is 1/2, and the probability of yellow beak (rr) from Rr x rr is 1/2. Therefore, the combined probability is (1/2) * (1/2) = 1/4.

All tall plants

All short plants

Half tall and half short plants

Three tall and one short plant

Correct Answer: A

Solution:

In the F1 generation, all offspring will be heterozygous (Tt) and express the dominant tall phenotype.

By altering the organism's environment.

By providing information for protein synthesis.

By directly changing the organism's behavior.

By determining the organism's diet.

Correct Answer: B

Solution:

Genes control characteristics by providing information for protein synthesis, which affects traits like plant height.

By the mother's genes only

By the father's genes only

By the combination of X and Y chromosomes

Randomly during fertilization

Correct Answer: C

Solution:

In humans, the sex of a child is determined by the combination of sex chromosomes inherited from the parents. The mother always contributes an X chromosome, while the father can contribute either an X or a Y chromosome. An XX combination results in a female child, while an XY combination results in a male child.

It is expressed only when two copies are present.

It is expressed even if only one copy is present.

It is never expressed in the offspring.

It is expressed only in the presence of a recessive trait.

Correct Answer: B

Solution:

A dominant trait is expressed even if only one copy is present, unlike a recessive trait which requires two copies to be expressed.

By the mother's chromosomes only

By the father's chromosomes only

By environmental factors

By both parents equally

Correct Answer: B

Solution:

In humans, the sex of a child is determined by the father's chromosomes. If the father contributes an X chromosome, the child will be female (XX), and if a Y chromosome, the child will be male (XY).

Sugarcane reproduces asexually.

Sugarcane has a high mutation rate.

Sugarcane is genetically modified.

Sugarcane undergoes sexual reproduction.

Correct Answer: A

Solution:

Sugarcane reproduces asexually, which results in less genetic variation among the plants.

True or False

Correct Answer: True

Solution:

Asexual reproduction can result in minor differences between offspring due to small inaccuracies in DNA replication.

Correct Answer: True

Solution:

In asexual reproduction, the offspring are generally very similar to the parent organism, with variations arising mainly from minor inaccuracies in DNA replication.

Correct Answer: True

Solution:

Mendel's experiments showed that different traits, such as seed shape and seed color in peas, are inherited independently, leading to new combinations in the offspring.

Correct Answer: True

Solution:

Mendel's experiments showed that traits like seed shape and plant height are inherited independently, allowing for new combinations of traits in the offspring.

Correct Answer: False

Solution:

Mendel's experiments showed that traits are inherited as discrete units, not as a blend.

Correct Answer: True

Solution:

Asexual reproduction results in offspring that are very similar to the parent, with variations arising mainly from minor DNA copying errors.

Correct Answer: True

Solution:

Mendel's experiments demonstrated that in the F1 generation, only the dominant trait was expressed, while the recessive trait was not visible, indicating no mixture of traits.

Correct Answer: False

Solution:

Even in asexual reproduction, small inaccuracies in DNA copying can lead to minor variations among the offspring.

Correct Answer: False

Solution:

The sex of a child is determined by the chromosome inherited from the father. If the child inherits an X chromosome from the father, it will be a girl; if a Y chromosome, it will be a boy.

Correct Answer: False

Solution:

Typically, one gene controls one trait, although there are cases where a single gene can influence multiple traits, known as pleiotropy. However, this is not the norm.

Correct Answer: False

Solution:

In Mendel's pea plant experiments, the trait for tall plants was dominant, while the trait for short plants was recessive.

Correct Answer: True

Solution:

Sexual reproduction involves the combination of genetic material from both parents, influencing traits in the offspring.

Correct Answer: True

Solution:

In asexual reproduction, variations arise primarily due to small inaccuracies in DNA copying, leading to minor differences between individuals.

Correct Answer: True

Solution:

In asexually reproducing organisms, variations can occur due to small inaccuracies in DNA copying, even though they reproduce without genetic contribution from another organism.

Correct Answer: True

Solution:

Mendel's experiments demonstrated that traits such as seed shape and color are inherited independently.

Correct Answer: True

Solution:

In sexually reproducing organisms, each parent contributes one set of chromosomes to the offspring, resulting in equal genetic contribution. This is why traits can be influenced by both paternal and maternal DNA.

Correct Answer: False

Solution:

While asexually reproducing organisms produce offspring that are very similar to the parent, minor variations can occur due to inaccuracies in DNA copying.

Correct Answer: False

Solution:

In Mendel's experiments, the F1 generation did not show a blend of traits. Instead, only the dominant trait was expressed, such as tallness in pea plants.

Correct Answer: False

Solution:

Environmental factors play a crucial role in the survival of variations, as they can select for traits that provide advantages in specific conditions.

Correct Answer: False

Solution:

Sugarcane plants in a field show very little variation among individual plants.

Correct Answer: True

Solution:

Mendel's experiments with pea plants showed that traits such as tallness can be dominant, while others like shortness can be recessive.

Correct Answer: False

Solution:

In sexually reproducing organisms, both the father and the mother contribute practically equal amounts of genetic material to the offspring, ensuring that each trait can be influenced by both paternal and maternal DNA.

Correct Answer: True

Solution:

Mendel's experiments showed that traits are inherited independently, allowing for new trait combinations in offspring.

Correct Answer: True

Solution:

Environmental factors can select for certain variations that offer a survival advantage, influencing which variations persist in a population.

Correct Answer: True

Solution:

Mendel's experiments with pea plants showed that traits are inherited as discrete units, now known as genes, which do not blend but are passed on intact from one generation to the next.

Correct Answer: False

Solution:

The sex of a child is determined by the chromosome inherited from the father: an X chromosome results in a girl, and a Y chromosome results in a boy.

Correct Answer: False

Solution:

In Mendel's experiments, the F1 generation showed only one of the parental traits, indicating dominance.

Correct Answer: True

Solution:

Sexually reproducing organisms inherit one set of genes from each parent, resulting in two sets of genes in total.

Correct Answer: False

Solution:

Variations in a species are not equally likely to survive; their survival depends on the environmental conditions and the nature of the variations.

Correct Answer: False

Solution:

In asexual reproduction, offspring are very similar to the parent but not genetically identical due to minor variations caused by small inaccuracies in DNA copying.

Correct Answer: True

Solution:

The sex of a human child is determined by the chromosome inherited from the father. If the child inherits an X chromosome, it will be a girl, and if it inherits a Y chromosome, it will be a boy.

Correct Answer: True

Solution:

In sexually reproducing organisms, each parent contributes one set of chromosomes, which includes one set of genes, to the offspring. This ensures genetic diversity and stability of the species.

Correct Answer: False

Solution:

In sexually reproducing organisms, variations are not solely due to inaccuracies in DNA copying. They also arise from the combination of genetic material from two parents, which increases diversity.

Correct Answer: True

Solution:

Sexual reproduction involves the independent inheritance of traits, allowing for new trait combinations in offspring.

Correct Answer: True

Solution:

Variations can provide certain individuals with advantages in specific environments, such as heat-resistant bacteria surviving better in heat waves.

Correct Answer: False

Solution:

Variations can affect survival chances. For example, bacteria that can withstand heat will survive better in a heat wave, demonstrating that variations can provide advantages in certain environments.

Correct Answer: False

Solution:

While many had studied inheritance before, Mendel was the first to apply a scientific and mathematical approach, leading to the formulation of the laws of inheritance.

Correct Answer: True

Solution:

Environmental factors can select for certain variations, influencing evolutionary processes.

Correct Answer: True

Solution:

Sexual reproduction involves the combination of genetic material from two parents, leading to greater diversity.

Correct Answer: False

Solution:

Mendel's experiments demonstrated that traits are inherited independently, as shown by the formation of new trait combinations in the F2 generation.

Correct Answer: False

Solution:

In asexual reproduction, offspring are similar but may have minor differences due to inaccuracies in DNA copying.

Correct Answer: False

Solution:

Mendel's experiments showed that the F1 generation displayed only the dominant trait, not a mixture of traits. For example, crossing tall and short plants resulted in all tall plants in the F1 generation.

Correct Answer: True

Solution:

Each parent contributes one set of chromosomes, ensuring that the offspring inherit genetic material equally from both.

Correct Answer: False

Solution:

The sex of an individual is determined by the chromosome inherited from the father, either X or Y.

Correct Answer: False

Solution:

Environmental factors select for certain variations that provide survival advantages, forming the basis for evolutionary processes.

Heredity and Evolution

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CBSE Learning Objectives – Key Concepts & Skills You Must Know

CBSE Revision Notes & Quick Summary for Last-Minute Study

Chapter 8: Heredity

8.1 Accumulation of Variation During Reproduction

8.2 Heredity

8.2.1 Inherited Traits

8.2.2 Rules for the Inheritance of Traits

Sex Determination in Humans

Important Diagrams

CBSE Exam Tips, Important Questions & Common Mistakes to Avoid

Common Mistakes and Exam Tips

Common Pitfalls

Exam Tips

Multiple Choice Questions

Correct Answer: A

Q2.Which of the following statements about Mendel's experiments is true?

Correct Answer: B

Q3.Why do sexually reproducing organisms have two copies of genes for the same trait?

Correct Answer: B

Q4.A geneticist is studying a plant species where the gene for seed texture has two alleles: S (smooth) and s (rough). If a plant with genotype Ss is crossed with a plant with genotype ss, what is the probability that an offspring will have smooth seeds?

Correct Answer: B

Q5.In a breeding experiment with a certain species of fish, it is observed that the gene for fin shape has two alleles: F (fanned fins) and f (straight fins). If two fish with fanned fins (Ff) are crossed, what is the expected ratio of fanned to straight fins in their offspring?

Correct Answer: B

Q6.In a certain animal species, the gene for tail length is influenced by two alleles: L (long tail) and l (short tail). If a long-tailed animal (Ll) is crossed with a short-tailed animal (ll), what proportion of the offspring will have short tails?

Correct Answer: C

Q7.Which of the following statements about the inheritance of traits is true according to Mendel's experiments?

Correct Answer: B

Q8.Which of the following traits is considered dominant in pea plants according to Mendel's experiments?

Correct Answer: C

Q9.In Mendel's experiments, what was the outcome when tall pea plants (Tt) were self-pollinated?

Correct Answer: C

Q10.In a certain species of fish, the trait for fin length is controlled by a pair of alleles: long fins (L) and short fins (l). If a fish with genotype Ll is crossed with a fish with genotype ll, what percentage of the offspring are expected to have short fins?

Correct Answer: B

Correct Answer: B

Q12.How does sexual reproduction contribute to genetic variation?

Correct Answer: C

Q13.In Mendel's experiments, what was the result of crossing a tall plant with round seeds with a short plant with wrinkled seeds?

Correct Answer: B

Correct Answer: A

Q15.What is the role of environmental factors in the survival of variations within a species?

Correct Answer: B

Q16.In a breeding experiment with pea plants, a researcher crosses a tall plant with round seeds (TtRr) with a short plant with wrinkled seeds (ttrr). What proportion of the offspring will be tall with wrinkled seeds?

Correct Answer: D

Q17.What determines the traits expressed in the offspring of sexually reproducing organisms?

Correct Answer: C

Q18.In a certain species of fish, the gene for scale color has two alleles: B (blue) and b (green). If two heterozygous blue-scaled fish (Bb) are crossed, what is the probability that their offspring will have green scales?

Correct Answer: A

Q19.In a population of insects, a rare mutation allows some individuals to survive pesticide exposure. If the mutation is present in 5% of the population, what is the probability that in a sample of 10 insects, none will have the mutation?

Correct Answer: B

Q20.If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

Correct Answer: B

Q21.What is the primary source of genetic variation in sexually reproducing organisms?

Correct Answer: C

Q22.A geneticist is studying a new species of insect where the gene for wing pattern has two alleles: D (dotted) and d (striped). If two heterozygous insects (Dd) are crossed, what is the probability that their offspring will have striped wings?

Correct Answer: A

Q23.In a breeding experiment with a certain plant species, a researcher crosses a plant with genotype AaBb with another plant of genotype aabb. What is the probability that an offspring will have the genotype Aabb?

Correct Answer: A

Q24.Consider a plant species where the gene for flower shape has two alleles: round (R) and oval (r). If a round-flowered plant (RR) is crossed with an oval-flowered plant (rr), what will be the genotype of the F1 generation?

Correct Answer: B

Q25.What ensures the stability of DNA in sexually reproducing organisms?

Correct Answer: C

Q26.In human beings, if a woman with blood group O marries a man with blood group A, which of the following blood groups could their children potentially have?

Correct Answer: C

Q27.If a plant with genotype Tt is crossed with a plant with genotype tt, what is the expected ratio of tall to short plants?

Correct Answer: A

Q28.Which of the following statements about the inheritance of traits is true?

Correct Answer: B

Q29.In Mendel's experiments, what was observed in the F2 generation when F1 tall pea plants were self-pollinated?

Correct Answer: C

Q30.In a study of a species of birds, it is found that a gene controlling feather color has two alleles: B (black) and b (brown). If two heterozygous birds (Bb) mate, what is the probability that their offspring will have brown feathers?

Correct Answer: A

Q31.In humans, what determines the sex of a child?

Correct Answer: B

Q32.Which of the following statements is true regarding the inheritance of traits according to Mendel's laws?

Correct Answer: B

Q33.In a study of a bird species, feather color is determined by a single gene with two alleles: red (R) and brown (r). If two heterozygous birds (Rr) are crossed, what is the expected phenotypic ratio of the offspring?

Correct Answer: A

Q34.In a hypothetical population of asexually reproducing bacteria, a mutation allows some bacteria to survive in acidic environments. If this trait is present in 20% of the population, what is the probability that in a random sample of 5 bacteria, at least one will have the mutation?