HRR: mendelian gentics

Question 1

Describe Mendel’s 1st law

Answer 1

Law of segregation (1st law): Hereditary traits are determined by discrete factors (genes) that occur in pairs and segregate (separate) during transmission to
offspring. Segregation is random.

Question 2

describe mendel’s second law

Answer 2

Traits at different genetic loci assort independently (ex: height is independent from eye color

Question 3

describe the exception to mendel’s second law

Answer 3

An exception is if two traits are physically linked to each other on the same chromosome

Question 4

Specify the genotype and phenotype ratios for the F1 & F2 generations of
homozygous dominant and homozygous recessive parents.

Question 5

describe autosomal dominant inheritance

Answer 5

only copy of a mutation is sufficient to cause a disease; seen on a pedigree as impacting multiple generations and in both sexes. Children with a parent with an autosomal dominant mutation has a 50% chance of inheritance

Question 6

name an example of an autosomal dominant condition

Answer 6

Huntington’s; progressive loss of motor control, cognitive and psychiatric problems. Considered 100% penetrant. Death usually occurs within 15 years, and age of onset is typically 30-45.

Question 7

describe autosomal recessive inheritance

Answer 7

two copies of a mutation are required to cause disease; typically, the parents are healthy carriers. If both parents are carriers, the offspring have a 25% risk. Equally transmitted by men and women. Carrier screening can allow people to determine what conditions they may be carriers for.

Question 8

name an example of autosomal recessive inheritance

Answer 8

Tay-Sachs is more common is Ashkenazi jewish ancestry, French-canadians, cajuns, PA amish. Causes progressive neurodegeneration, seizures, blindness, spasticity. Onset around 3-6 months, typically with death before age 4

Question 9

describe x linked dominant inheritance

Answer 9

impacts both males and females, but males have the potential to have more severe impacts. There are no carriers; if you have the mutation, you have the condition. If a father is affected, the daughter has a 100% risk, where the son has a 0% risk. Daughters get their father’s X, and son’s get their fathers Y. women have a 50% risk of passing to the child regardless of gender.

Question 10

describe x linked recessive inheritance

Answer 10

genes are on the x chromosome; females typically need two copies to be affected, as the non-mutated X can “mask” the effects of the mutated X. men will express the condition as they have one X chromosome

Question 11

give an example of x linked recessive inheritance

Answer 11

Duchenne muscular dystrophy causes progressive muscle degeneration and weakness. Typically, has affected males and unaffected females. 1/3 of cases are due to new mutations, not inherited ones. Female carriers have an increased risk for cardiomyopathy

Question 12

describe co dominant inheritance

Answer 12

two alleles impact the phenotype equally. Ex is ABO blood type. A and B are co dominant to O.

Question 13

give an example of co dominant inheritance

Answer 13

alpha-1 antitrypsin deficiency is a single gene risk for lung and liver disease. With normal being M and Z being mutated, MZ causes a mildly reduced AAT, providing some increased risks for lung and liver disease. ZZ would cause severe AAT deficiency and cause high risks for lung and liver disease.

Question 14

Answer 14

Question 15

describe reduced penetrance

Answer 15

penetrance is the probability a genotype will express the phenotype. In reduced penetrance, some with the disease genotype have no phenotypic manifestations.

Question 16

describe variable expressivity

Answer 16

When the type or severity of manifestations differs in individuals with the same genotype. Ex: NF1 can cause café au lait spots, learning disabilities, and brain tumors/optic nerve gliomas

Question 17

describe pleiotropy

Answer 17

a single genetic mutation. Impacts multiple organ systems. Ex: marfans, cystic fibrosis, alport syndrome

Question 18

describe heterogenity

Answer 18

Mutations in multiple unrelated genes cause the same or similar phenotype. Ex: BRCA ½ both cause predisposition to breast and ovarian cancer

Question 19

define consanguinity

Answer 19

When two people are related, it increases the risk for the inheritance of recessive trait, as they’re more likely to both be unimpacted carriers. This should be considered when the inherited disorder is quite rare.

Question 20

define pseudodominance

Answer 20

When an autosomal recessive disease is seen in multiple generations

Question 21

when do we use pedigree vs population data?

Answer 21

We use pedigree to find carrier risk when there is a positive family history. To find carrier risk with no family history, we would use population genetics rules such as HWE

Question 22

person A has a sibling with an autosomal recessive disease, but they themselves do not have it. what is their risk of passing on the condition?

Answer 22

2/3

Question 23

what is genetics drift?

Answer 23

random fluctuation of frequencies in small populations