Mendelian Genetics

Question 1

Dominant

Answer 1

Heterozygous with one copy of the altered gene are affected

- 2 alleles (one normal, one mutated)

Question 2

Recessive

Answer 2

Homozygotes with 2 copies of altered gene are affected. Can also act in different form of heterozygotes

Question 3

X-linked

Answer 3

Gene causing disorder is located on X chromosome (can be recessive or dominant)

Question 4

X-linked dominant

Answer 4

• Mutation on gene on X chromosome
• In females (XX) - a mutation in one of these copies is sufficient
  In males (XY) - Mutation in X causes disorder

Males experience more severe symptoms. Fathers cannot pass X-linked traits to their sons

Question 5

X-linked recessive

Answer 5

In males - one altered copy of X is sufficient to cause disorder
In females - Mutation would have to occur in both copies of X to cause disorder (rare)

Fathers cannot pass X-linked traits to sons

Question 6

Homozygous

Answer 6

Organism has 2 copies of same allele for gene

Question 7

Heterozygous

Answer 7

Organism has 2 different alleles of gene

Question 8

Homozygous dominant/recessive

Answer 8

Organism carries 2 copies of same dominant/recessive allele

Question 9

Autosomal dominant

Answer 9

One mutated copy of gene in each cell is enough to cause disease - heterozygotes with one copy of mutated gene are affected

50% risk of affected offspring

Question 10

Examples of autosomal dominant conditions?

Answer 10

Huntington’s, neurofibromatosis, adult polycystic kidney disease

Question 11

Autosomal recessive

Answer 11

Must be homozygous recessive to be affected (requires both parents to at least be carriers)

25% risk of affected offspring
50% risk of carrier offspring

Question 12

Examples of autosomal recessive conditions?

Answer 12

Cystic fibrosis, phenylketonuria, spinal muscular atrophy, congenital adrenal hyperplasia