Question

An inherited disease in a mom that affects all children regardless of sex, but then occurs in only and all granddaughters is likely to be caused by:

	a.	A mutation in a gene on a non-sex chromosome (autosome)
	b.	A mutation in a gene located on the mitochondrial chromosome
	c.	A mutation in a gene on the Y chromosome
	d.	A mutation in a gene on the X chromosome

Answer 1

ansr) A muation in a gene on the X chromosome.

normal father affected mother(HOMOZYGOUS)

FATHER/MOTHER	X	XY
X	XX(Affected)(HETEROZYGOUS)	XY(Affected)
X	XX(Affected)(HETEROZYGOUS)	XY(Affected)

all are affected because of the one X linked dominant allele of the mother.

In the next generation,

Affected male normal female

male/female	X	Y
X	XX(Females affected)	XY(NON AFFECTED MALE)
X	XX(Female affected)	XY(NON AFFECTED MALE)