Page 64 - Biology - XII

SPOT - 3

Fig. 11.7: (i) Normal free earlobes (ii) Fused earlobes

A Pedigree Chart of Family for Earlobes

Generation I

Male
Generation II
Off spring Female
1 2 9

Trait in female
Generation III
Off spring
1 2 3 4 5 6 7 8

Fig. 11.8: Pedigree of a family (hypothetical) in which a trait-fused earlobes are shown (phenotype)

The trait (fused earlobes) produced by a recessive gene appeared in generation I in off spring- 2 (daughter).
Aa Aa

Aa AA aa AA AA Aa

1 2 3 Aa 4 Aa 5 6 7 8

Probability of being Aa is 1/3 Probability of being Aa is 1/3

Fig. 11.9: Pedigree of a family (hypothetical) in which a trait-fused earlobes are shown (genotype)

Comments
1. To express the trait, the female/daughter must be homozygous recessive, i.e. aa.
2. Parents who are heterozygous (Aa) for the trait are having normal earlobes.
3. The siblings receive a gene each from the parents. Therefore, in generation-II daughter 1 has genotype
(AA) or (Aa), daughter 2 has genotype (aa), brother 3 has genotype (AA) or (Aa), but not (aa).

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