Name: Sex Determination (Drosophila melanogaster)
Uploaded: 2019-07-19
Duration: 7 min 20 s
Description: Drosophila melanogaster or the common fruit fly has contributed a lot to genetics. One of them is its sex determination system with more than five types of s...

Question

In humans, the allele for red hair, b is recessive to the allele for brown hair, B. A man and his wife both have brown hair. They have five children, three of whom have red hair, while two have brown hair. Explain how this may happen, using a genetic diagram to explain the answer.

Accepted Answer

A dominant allele is represented by a capital letter and the recessive one is in a small letter. The genetic makeup of an organism in terms of the alleles present is called the genotype. In humans, the allele for brown hair is B which is dominant over red hair (b) which is a recessive character. Here, the father and mother both have brown hair. Brown hair is the dominant character that could have either of two possible genotypes, BB and Bb. The red hair occurs in a condition in which both alleles are recessive (bb). It is possible only when both the parents are heterozygous in hair colour. The cross is given below:

In this cross, The human with heterozygous brown hair produces half of the gametes have the genotype B and half have the genotype b. Hence, two types of eggs and sperms are produced (B and b). The resultant offspring are 75% brown-haired and 25 % are red-haired. Hence, it is possible to produce red-haired offspring from brown-haired parents, if both are heterozygous.

In humans, the allele for red hair, b is recessive to the allele for brown hair, B. A man and his wife both have brown hair. They have five children, three of whom have red hair, while two have brown hair. Explain how this may happen, using a genetic diagram to explain the answer.

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