Question

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1. (20 points) a. The short pedigree below shows affected individuals in this family in red. Which modes of inheritance (X-linked recessive, X-linked dominant, Y-linked, autosomal recessive, autosomal dominant) can be ruled out, and which mode is most likely? b. (10 points) What is the likelihood that child A will be affected? Child B? O ■ ● Co

Answer 1

This is the example of an X linked DOMINANT trait. Here 50% of daughters and 50% of sons are affected and the remaining 50% sons and 50% of daughters are normal.

XX x XY

	X	X
X	XX	XX
Y	XY	XY

X linked recessive can be ruled out as here males are much more affected because they have only one copy of X chromosomes and if that copy becomes mutant or they inherit that mutant copy they become the affected one. Females are usually carriers.

An autosomal recessive mode of inheritance can be ruled out as in this type of inheritance a person who has two copies of the altered gene manifests the trait, but heterozygotes (carriers) are unaffected. Autosomal recessive disorders are typically not seen in every generation of an affected family.

The autosomal dominant condition can be ruled out as One mutated copy of the gene in each cell is sufficient for a person to be affected by an autosomal dominant disorder.

Y linked condition can be ruled out as hee the trait is only passed on from fathers to sons.

B. Mother of A is normal and the father of A is also normal. So the likelihood of A being affected is 0%.

Father of B is normal and the mother is also normal so the likelihood of B being affected is 0%.