Q79 of 167 Page 195

Mendel first crossed pure-bred pea plants having round-yellow seeds with pure-bred pea plants having wrinkled-green seeds and found that only round-yellow seeds were produced in the F1 generation. When F1 generation pea plants having round-yellow seeds were cross-bred by self-pollination, then peas having round � yellow seeds, round green seeds, wrinkled-yellow seeds and wrinkled-green seeds were produced. Mendel collected a total of 2160 seeds.

(a)What will be the number of?


(i) Round green seeds


(ii) Wrinkled green seeds


(iii) Round yellow seeds, and


(iv) Wrinkled-yellow seeds


(b) Which 'ratio' as established by Mendel have you made use of in answering the part (a) above?

(a) The F2 generation obtained had Round yellow: Round green: Wrinkled yellow: Wrinkled green in the ratio 9:3:3:1

(i) Round Green seeds- (3/16)*2160= 405


(ii) Wrinkled Green seeds- (1/16)*2160= 135


(iii) Round yellow seeds- (9/16)*2160= 1215


(iv) Wrinkled yellow seeds- (3/16)*2160= 405


(b) Dihybrid ratio has been used in answering this question because here are two different varieties, that differ in two observed traits i.e. Shape : round and wrinkled; Color: yellow and green.


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77

A person first crossed pure-bred pea plants having round-yellow seeds with pure-bred pea plants having wrinkled-green seeds and found that only A-B type of seeds were produced in the F1generation. When F1 generation pea plants having A-B type of seeds were cross-bred by self-pollination, then in addition to the original round-yellow and wrinkled-green seeds, two new varieties A-D and C-B type of seeds were also obtained.

(a) What are A-B type of seeds?


(b) State whether A and B are dominant traits or recessive traits.


(c) What are A-D type of seeds?


(d) What are C-B type of seeds?


(e) Out of A-B and A-D types of seeds, which one will be produced in


(i) minimum numbers, and


(ii) maximum numbers, in the F2 generation ?

78

The person A has only B chromosomes in all its gametes. On the other hand, another person C has chromosome D in half of gametes and chromosome E in the other half of gametes. When chromosomes B and D combine during fertilization, a female zygote results. On the other hand, combination of B and E chromosomes produces a male zygote.

(a) What are chromosomes?


(i) B


(ii) D, and


(iii) E ?


(b) Out of B, D and E, which two chromosomes are of the same type?


(c) Which chromosome is smaller in size?


(d) What is the general name of chromosomes such as B and E?


(e) Out of the two persons A and C, which one is


(i) male, and


(ii) female ?

80

Pure-bred round-yellow pea seeds have genotype RRYY and the pure-bred wrinkled-green pea seeds have genotype rryy. Keeping this in mind, write the phenotypes of the following genotypes of hybrid pea seeds:

(a) Rryy


(b) rrYy


(c) rrYY


(d) RrYy


(e) RRyy

1

What name is given to the sequence of gradual changes over millions of years in which new species are produced?