Shown below is the pedigree of a rare neurodegenerative disease in humans. a. Ba

Question

Shown below is the pedigree of a rare neurodegenerative disease in humans.

a.    Based on the pedigree, characterize each of the following modes of inheritance as likely, unlikely, or impossible: autosomal dominant, autosomal recessive, Y linked, X-linked dominant, and X-linked recessive. Justify your reasoning.  

Further scrutiny of members of this family reveals the following: 1) The disease’s degree of expression varies among individuals, with some mildly affected, others moderately affected and still others severely affected; and 2) Individual III-14 was previously married. Her ex-husband is phenotypically normal, with no history of the disease in his family going back ten generations. He has custody of the couple’s two children, a girl and a boy, both of whom are affected with the disease. The partial pedigree is shown below (the “slash” represents separation or divorce)

b.    Do these findings eliminate any of the remaining “likely or unlikely” modes of inheritance listed in part (a)? Are any of these modes of inheritance still possible? If so, which one(s) and why?

c.     Is mitochondrial inheritance a likely, unlikely or an impossible mode of inheritance for this disease? Does it provide an explanation for the disease’s variable expressivity?

d.    How can mitochondrial inheritance explain individual III-14?

Explanation / Answer

The pedigree is not given,

Explaination of the inheritance patterns

Autosomal dominant ; 1. Child of affected parent has 50% chance of inheriting the trait.

2. One allele is required for a person to be affected. Therefore the phenotype of the disease appears in every generation

3. Both males and females affected equally

Autosomal recessive;

1.The parent of the affected usaully will not be affected

2. Affected individuals do not occur in each generation

3. Consanguinity is increased in the parents of the affected individuals

X- linked recessive;

1. No father-son transmission of disease

2. Males are more likely to be affected than females

3. All daughters of the affected man are carriers

X-linked dominant

1. There is no father - son transmission of disease

2. Females are more likely to be affected

3. Characteristics are similar to autosomal dominant

4. all offspring of a homozygous femal are affected and half the offspring of heterozygous female are affected

b. Autosomal dominant and autosomal recessive inheritance patterns are reported in neurodegenerative diseases the disease genes are seen in autosomes and not in sex chromosomes.

c. Mitochondrial inheritance; This mode of inheritance is possible in neurodegenerative diseases. In neurodegenerative disoders mitochondrial dysfunction may be secondary causative factor

d. Affected male does not pass the disease so all his children unaffected. mitochondria pass through ova and not sperm

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