Inheritance; This is interesting

Biology Level 1

The image above represents the pedigree chart of a family with five children. It shows the inheritance of attached ear lobes as opposed to the free ones. The squares represent the male individuals and circles the female individuals.

Which of the following conclusions drawn is correct?

The parents are homozygous recessive The parents are homozygous dominant The parents are heterozygous The trait is Y-linked

1 solution

Josh Silverman Staff
May 1, 2014

Consider the possibility that the parents are homozygous (dominant or recessive). If $\mathbf{E}$ denotes the dominant trait and $\mathbf{e}$ , the recessive trait, then the possibilities for the children under either scheme is $\mathbf{EE}$ , or $\mathbf{ee}$ .

If the trait were y-linked, we'd expect to find that only one sex can have the trait. It is clear from inspection that members of either sex have either outcome, so this can't be true.

The last remaining choice, that the parents are heterozygous, can explain the outcome. The Punnet square for two heterozygous parents (and a non sex-linked trait) produces progeny of both phenotypes and all genotypes.

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|  |E |e |
|E |EE|Ee|
|e |eE|ee|

I realised that although both the parents have free ear lobes, but two of their children have attached earlobes. This means that the parents had the attaches earlobe trait, but it was recessive and was not expressed. So, the parents have to be heterozygous

Krishna Ramesh - 7 years, 1 month ago

Inheritance; This is interesting

1 solution

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