Q70 of 167 Page 195

A red-haired woman marries a brown-haired man, and all the children are brown haired. Explain this genetically.

Brown hair color genes are dominant and the red hair color genes are recessive ; The genotype of brown hair is BB (dominant always represented by capital letter) and that of red hair bb (Recessive represented by small letter)


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68

Pure-bred tall pea plants are first crossed with pure-bred dwarf pea plants. The pea plants obtained in F1 generation are then cross-bred to produce F2 generation of pea plants.

(a) What do the plants of F1 generation look like ?


(b) What is the ratio of tall plants to dwarf plants in F2 generation?


(c) Which type of plants were missing in F1 generation but reappeared in F2 generation?

 69

A plant has two varieties, one with red petals and the other with white petals. When these two varieties are cross-pollinated, all the offspring have red petals?

(a) Which gene is dominant?


(b) Choose suitable letters to represent the two genes.

 71

A black mouse mates with a brown mouse, and all the offspring are black.

(a) Why are no brown off springs produced?


(b) If two of the black offspring mate with each other what kind of offspring would you expect and in what proportions? Give reason for your answer.

 72

(a) E is the gene for brown eye color and e is the gene for blue eye color. Which gene is

(i) Recessive, and


(ii) Dominant


(b) Both father and mother have the genes Ee in their cells. What color are their eyes?


(c) Which combination of genes in the zygote will produce children with blue eyes?


(d) Which combinations of genes in the zygote will produce children with brown eyes?