Mendelian Inheritance and Pedigree Analysis

Question 1

Define penetrance (2)

Answer 1

1) Freq that the phenotype appears when ind’s have inherited the gene
2) Prop of gene carriers who have clinical symptoms

Question 2

Define variable expressivity

Answer 2

1) Extent that the genetic disorder is clinically evident in an ind who carries the gene
2) Same gene may cause a diff phenotype in diff family members

Question 3

What do anchondroplasia, neurofibromatosis (NF), and ontogenesis imperfecta (OI) have in common?

Answer 3

Autosomal dominant disorders w/ increased new mutation rates

Question 4

Define heterogeneity

Answer 4

Different genes or genetic mutations causing same phenoytpe (clinically indistinguishable)

Question 5

Examples of heterogeneity?

Answer 5

• 4 known genes for Wardenberg’s and albinism

Question 6

Define allelic (intralocus) heterogeneity

Answer 6

• diff mutations w/i 1 gene that –> same disorder

Question 7

Define locus (interlocus) heterogeneity

Answer 7

• mutations in diff genes that –> same disorder

Question 8

Examples of disorders where variable expressivity is related to allelic heterogeneity? (3)

Answer 8

1. PKU
2. Cystic fibrosis
3. Neurofibromatosis

Question 9

Describe Lyon Hypothesis (2)

Answer 9

• inactivation of one random X chromo in each cell in a female
• heterozygote –> hemizygote