Question

3) Children with ALD (pedigree at the left) have progressive brain damage. adrenal failure, and eventual death. TO O O Which of the following terms describes the disease-causing allele? a) pleiotropic b) dominant c) recessive d) polygenic 4) What is the most likely mode of transmission? 5) What is the genotype of the woman in the first generation?

Answer 1

3) Answer: c) Recessive

• Pdigree analysis: If the offspring are affected, but the parents are not affected (as they are heterozygous), then the condition is recessive.

4) Answer: X-linked.

• The X-linked traits are governed only by allele of X chromosome gene.
• X-linked inheritance affects mostly males. Males are affected in the pedigree, female passes the disease to males- sex linked. X-linked genes are transmitted from father to daughters and not to sons.
• ALD is Adrenoleukodystropy.
• It is prominent in males and is inherited as X-linked disorder.
• The condition affects the Adrenal gland and the nervous system.

5)

Representation:

Since the affected condition is recessive condition, representing as a, corresponding normal state as A.

Thus, genotypes may be represented as:

• Affected Male: Xa Y (hemizygous, recessive)
• Normal Male: XAY (hemizygous, dominant)
• Affected Female: XaXa (homozygous, recessive)
• Normal Female (carrier): XAXa (heterozygous, dominant)
• Since, the trait is passed from females to next to next generation male. The female of generation I and generation II are carriers.
• Genotype is heterozygous- XAXa