CBSE Class 10 Science Heredity Worksheet Set 05

Answer: (b) Round, yellow and wrinkled, green. The parents were round green and wrinkled yellow, so the new combinations are round yellow and wrinkled green.

Teacher's Note:
1. New combinations show that traits are inherited independently.
2. Compare F2 types with the two parental types.

Answer: (c) Size of body. Body size depends partly on nutrition and health, so a change in it is acquired and not passed through DNA.

Teacher's Note:
1. Acquired traits do not change the DNA of germ cells.
2. Eye colour and hair nature are genetic.

Answer: (b) (i) and (iii). Genes are DNA segments that code for proteins and are located at fixed positions on chromosomes, and each chromosome has many genes.

Teacher's Note:
1. A chromosome carries many genes.
2. Genes control traits by making proteins.

Answer: (a) One. A human zygote has 23 pairs of chromosomes, of which one pair is the sex chromosomes (XX or XY).

Teacher's Note:
1. The other 22 pairs are autosomes.
2. Sex chromosomes decide whether the child is male or female.

Answer: (d) 4 tall plants and 1 medium height plant. Mendel's pea plants were either tall or short, so no medium height plants appear.

Teacher's Note:
1. Contrasting traits do not blend.
2. A 3 : 1 ratio is expected in F2.

Answer: (d) Natural selection can change the frequency of an inherited trait. Natural selection was not studied by Mendel; it comes from evolutionary theory.

Teacher's Note:
1. Mendel studied how traits pass between generations.
2. Dominance, pairs of factors and recessive expression came from his work.

Answer: (d) All of the above. In a dihybrid cross the F2 shows all four combinations of the two traits.

Teacher's Note:
1. The traits assort independently.
2. The ratio is 9 : 3 : 3 : 1.

Answer: (d) Gene. A gene is the DNA segment that codes for one protein.

Teacher's Note:
1. Chromosomes contain many genes.
2. Proteins control the expression of traits.

Answer: (a) 50%. The father produces X-bearing and Y-bearing sperms in equal numbers, so the chance is 1 in 2.

Teacher's Note:
1. The mother always gives an X chromosome.
2. The sperm decides the sex of the child.

Answer: (a) Girls only. Girls have XX, two matching chromosomes, while boys have XY, which are unequal.

Teacher's Note:
1. Y is smaller than X.
2. The pair XX is a perfect pair.

Answer: (c) Sexual reproduction. Sexual reproduction involves fusion of gametes from two parents, which mixes genetic material.

Teacher's Note:
1. Asexual methods have a single parent.
2. Variation comes from this mixing.

Answer: Sexual reproduction, because genes from two parents combine.

Teacher's Note:
1. Gametes carry different gene combinations.
2. Asexual offspring are nearly identical.

Answer: Free earlobes and attached earlobes.

Teacher's Note:
1. Earlobe type is an inherited trait.
2. Most people have free earlobes.

Answer: Trait B, because a trait that is present in more individuals has had longer to spread through copies of the parent.

Teacher's Note:
1. Variations in asexual reproduction are small and accumulate slowly.
2. A common trait has had more generations to spread.

Answer: Genes.

Teacher's Note:
1. Mendel did not know about DNA.
2. Each parent gives one copy of each gene.

Answer: Black, because the dominant black gene masks the recessive red gene.

Teacher's Note:
1. The person is a carrier of red hair.
2. A recessive trait appears only when both copies are recessive.

Answer: (a) Pairs.
(b) Recessive; dominant.

Teacher's Note:
1. A dominant gene hides the effect of a recessive gene in a pair.
2. Tallness is dominant in pea plants.

Answer: (c) Free; attached.
(d) 23; 46.

Teacher's Note:
1. Gametes have half the chromosome number.
2. Fusion of two gametes restores 46.

Answer: XX; XY.

Teacher's Note:
1. The Y chromosome is present only in males.
2. Females only give X-bearing eggs.

Answer: A gene is a DNA segment that carries the code for making a protein, and the protein controls a trait. For example, the gene for tallness in pea plants directs the making of a growth hormone in sufficient quantity, so the plant is tall, while a changed gene gives less hormone and a dwarf plant.

Teacher's Note:
1. Genes work by directing protein synthesis.
2. The amount of protein affects the trait.

Answer: (a) Variation increases the chances of survival of a species in a changing environment.
(b) Sex chromosomes are the pair of chromosomes that determine the sex of an individual. Humans have two, called X and Y.

Teacher's Note:
1. A species with varied members is less likely to be wiped out.
2. Females have XX and males have XY.

Answer: (a) tt.
(b) TT.

Teacher's Note:
1. Both are pure-bred (homozygous).
2. Tt plants are tall but give both kinds of offspring.

Answer: (a) (i) 23. (ii) 46.
(b) Tall : dwarf = 3 : 1, because TT, Tt, Tt are tall and tt is dwarf.

Teacher's Note:
1. Sperm is haploid and the zygote is diploid.
2. Tt x Tt gives genotypes in the ratio 1 : 2 : 1.

Answer: Mendel crossed pure tall and pure dwarf pea plants and got only tall plants in F1. When F1 plants were self-pollinated, tall and dwarf plants appeared in F2 in the ratio 3 : 1. This shows dwarfness was hidden, not lost, so tallness is dominant and dwarfness is recessive.

Teacher's Note:
1. The recessive trait reappears in F2.
2. Both F1 plants carry one copy of each factor.

Answer: Mendel crossed pure plants with round yellow seeds and wrinkled green seeds and got only round yellow seeds in F1. In F2 he found round green and wrinkled yellow seeds along with the parental types. New combinations show that seed shape and colour are inherited independently of each other.

Teacher's Note:
1. The F2 ratio is 9 : 3 : 3 : 1.
2. The new combinations are called recombinants.