Class 10 NCERT Solutions Biology Chapter 8 - Heredity and Evolution
Heredity and Evolution Exercise 129
Solution 1
As the population of the given species reproduce asexually there would be only very minor differences generated due to small inaccuracies in DNA copying, so trait B is likely to be arisen earlier as it is present in 60% of the population. Trait A which exists in 10% of the population may be originated due to variations.
Concept insight: More percentage of one trait in a population indicates the earlier evolution of that particular trait.
Solution 2
Favourable variations help a species to adapt to changes in their environment and they promote survival of a species.
Concept insight: List the advantages of variations.
Heredity and Evolution Exercise 133
Solution 1
Mendel took one tall pea plant and one short pea plant and produced progeny from them.
Parents: TT tt
(tall plant) (small plant)
Gametes: T T t t
Progeny: F1 Tt Tt
(tall plant)
F2 TT Tt tt
(tall) (tall) (short)
From this cross he found that in nature tallness is dominant over shortness. Because in F2 generation heterozygous plant contains one gene of tallness and one of shortness of which tallness expressed itself. Thus he concluded that in a contrasting pair of characters one character is dominant and another is recessive.
Concept insight: Recall Mendel's law of inheritance.
Solution 2
Mendel conducted a dihybrid cross. He took two characters:
(i) Round and yellow seeds (RRYY)
(ii) Wrinkled and green seeds (rryy)
In F1 generation, he got plants with Round and yellow seeds (RrYy) Then he self crossed F1 plants. He got the following result:
(i) Round yellow - 9
(ii) Round green - 3
(iii) Wrinkled yellow - 3
(iv) Wrinkled green- 1
From the following result, it can be concluded that genes controlling different characters are not linked. Thus, in F2 generation, he got two new characters (round, green and wrinkled, yellow) other than parental characters (round, yellow and wrinkled, green).
Concept insight: Recall Mendel's second law of inheritance.
Solution 3
No, the information provided is not enough to tell whether blood group A or O is dominant. Every character is controlled by a pair of alleles. And here, it is not mentioned whether the man and woman have homozygous or heterozygous traits.
Concept insight: Recall Mendel's law of inheritance.
Solution 4
Human male has one X-chromosome and one Y-chromosome. In other words, half the male gametes have X-chromosomes and the other half have Y-chromosomes. On the other hand, a female has two X-chromosomes. Thus all female gametes have only X-chromosomes. If a sperm carrying Y-chromosome fertilizes an ovum then the child born will be a boy. On the other hand, if a sperm carrying X-chromosomes fertilizes an ovum then the child born will be a girl.
Concept insight: Recall types of chromosomes in human beings.
Heredity and Evolution Exercise 133 Contd.
Solution 1
(c) TtWW
Concept insight: Recall Mendel's law of inheritance.
Solution 2
Only dominant traits are transferred from the parents to the offspring in the first generation. Therefore, it can be concluded that light eye colour is dominant.
Concept insight: Recall Mendel's law of inheritance.
Solution 3
Dogs have a variety of genes that govern coat colour. There are at least eleven identified. Gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dog. A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown.
Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb) gametes of black parent will be (B,B) and brown parent will be (b,b). In the F1 generation, all offsprings will be heterozygous (Bb). (1 mark)
Since black (B) is dominant, all the offsprings will be black. However, they will have both B and b alleles. If such heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offsprings.
Concept insight: Recall Mendel's law of inheritance.
Solution 4
During sexual reproduction, a female gamete (egg) fuses with a male gamete (sperm) which are haploid and forms a zygote. Zygote is diploid which contains 23 chromosomes from mother and 23 from father. In this way, an equal genetic contribution of male and female parents is ensured in the progeny.
Concept insight: Recall the mechanism of Sexual reproduction in human beings.
