You are working with a human genetics research group that is studying mutations

Question

You are working with a human genetics research group that is studying mutations in island populations. Your project focuses on finding novel mutations in genes responsible for encoding hair color. Below is a pedigree of a family from Britain. In order to minimize unconscious bias during analysis, your project leader has not told you the genotypes of the individuals, or the identity of the gene of interest. Only the phenotypes are represented, with blank shapes indicating wild-type (non-red) hair, and the filled-in shapes indicating red hair.

1. Based on the pedigree , is red hair a dominant or recessive trait? Give two pieces of scientific evidence (examples from the pedigree) to justify your answer. 1.5 pt.

2. Based on the pedigree , is red hair a sex-linked trait? Why or why not? Give two examples. 1.5 pt.

Explanation / Answer

1. From the pedigree guven above, the red hair trait appears only in one offspring of phenotypically normal parents in second generation. So the trait is a recessive one. If it had been dominant, one of the parents must have shown the phenotype of red hair. Example- generation I which is not having the phenotype produces two offspring, one with the phenotype and other is normal. Again, the offsprings produced by parent having this trait produces all normal offsprings in the 3rd generation.

2. As mentioned above, a recessive trait if sex linked, will only be expressed when found in heterozygous condition. But here, the trait is expressed independent of the sex so it is an autosomal recessuve trait. Example, 3rd generation produced from offspring 2 (normal) has all offsprings having red hair. Whereas, the trait having parent produces only normal offsprings. Had it benn an sex linked trait, either of the sexes of offsprings would show the phenotype, produced from individual 2 of 2nd generation.

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