8/25/14 - Patterns of Single Gene Inheritance

Question 1

What is consanguinity?

Answer 1

The genetic relationship that results from common ancestry. The more closely related 2 individuals are, the more likely they are to share alleles from a common ancestor.

Question 1

How is mitochondrial DNA inherited?

Answer 1

Maternally

Question 2

What are some characteristics of sex-linked recessive inheritance patterns?

Answer 2

-Affected fathers transmit disease to their grandsons through their daughters -All daughters of affected fathers are carriers -Female carriers have a 50% chance of transmitting the diseased allele to their children

Question 2

What are some characteristics of sex-linked dominant inheritance patterns?

Answer 2

-Affected fathers always transmit the disease to their daughters but never their sons -Female carriers have a 50% of transmitting the *disease* to their children

Question 3

What is penetrance?

Answer 3

The proportion of individuals possessing a mutant gene who exhibit clinical symptoms. In other words, not all individuals with a mutant allele will show disease symptoms.

Question 4

What is the coefficient of inbreeding?

Answer 4

1/2 x coefficient of relationship

Question 5

What are two examples of hemizygosity?

Answer 5

-Deleted gene results in only one copy at a given locus -Sex-linked genes in males

Question 6

Which gene, UBE3A or SNRNP, would you expect to be methylated in a patient with Angelman syndrome?

Answer 6

UBE3A. In AS, the deletion occurs on the maternal chromosome, leaving only the silenced paternal UBE3A. Since the patient inherited a healthy chromosome 15 from the father, you would expect SNRNP to be unmethylated/active.

Question 7

What is heteroplasmy?

Answer 7

There is more than one type of DNA in a cell. Ex. mitochondrial DNA

Question 9

What is hemizygosity?

Answer 9

Only possessing a single allele at a given locus.

Question 9

What is variable expressivity?

Answer 9

A difference in the severity of disease among patients with the same genotype. In other words, two individuals may have the same disease-causing allele, but one individual has far worse symptoms.

Question 10

What are some characteristics of autosomal dominant inheritance patterns?

Answer 10

-Phenotype is seen in heterozygotes -Males/females equally affected -Unaffected family members are unlikely to transmit the disease

Question 12

What is a compound heterozygote?

Answer 12

Individual who has 2 different mutant alleles at a given locus.

Question 12

What is the proband?

Answer 12

The first affected family member who seeks medical attention for a genetic disorder.

Question 12

What are the seven complications seen in basic inheritance patterns that lead to non-Mendelian inheritance?

Answer 12

1. De novo mutations 2. Genomic imprinting 3. Reduced penetrance 4. Variable expressivity 5. Phenotypic variability 6. Delayed onset 7. Small family size

Question 13

What are some characteristics of autosomal recessive inheritance patterns?

Answer 13

-Only homozygotes affected -Males/females equally affected -Parents are carriers

Question 14

What are 4 classic symptoms of Prader-Willi syndrome?

Answer 14

1. Hypogonadism 2. Mental retardation 3. Obesity 4. Hyperphagia

Question 16

What is incomplete dominance?

Answer 16

The phenotype resulting from a heterozygous genotype is distinct and often intermediate. Ex. red, *PINK*, white flowers

Question 17

What are the characteristics of Angelman syndrome? Include specific gene affected and imprinting pattern (not symptoms)

Answer 17

-Maternal UBE3A allele normally active, paternal allele normally silenced -In AS, maternal UBE3A is lost due to deletion, only silent paternal UBE3A is left -Most cases caused by deletion on Q-arm of chromosome 15

Question 18

What are 4 general features of mitochondrial DNA diseases?

Answer 18

1. Maternal inheritance 2. Reduced penetrance 3. Variable expressivity 4. Pleiotropy

Question 19

What is anticipation?

Answer 19

Genetic abnormalities worsen in subsequent generations. Common in tri-nucleotide repeat expansion disorders such as Huntingtons.

Question 20

How do you determine the degree of relationship?

Answer 20

Count the number of uninterrupted lines in a pedigree map that relate 2 family members

Question 21

What is the coefficient of relationship?

Answer 21

(1/2)^n, where n is the degree of the relationship

Question 23

What is haploinsufficiency?

Answer 23

One normal allele is insufficient to compensate for the loss of the other.

Question 24

What is pleiotropy?

Answer 24

The activity of one gene influences multiple phenotypic traits.

Question 25

What is codominance?

Answer 25

Both alleles are expressed in the heterozygous state. Ex. Flowers with red and white coloration

Question 26

What is mosaicism?

Answer 26

A mutation during cell proliferation that leads to a proportion of cells carrying the mutation, while others remain normal.

Question 28

Which gene, UBE3A or SNRNP, would you expect to be methylated in a patient with Prader-Willi syndrome?

Answer 28

SNRNP. In PWS, the deletion occurs on the paternal chromosome, leaving only the silenced maternal SNRNP. Since the patient inherited a normal chromosome 15 from the mother, you would expect UBE3A to be unmethylated/active.

Question 29

What are 4 classic symptoms of Angelman syndrome?

Answer 29

1. Excessive laughter 2. Seizures 3. Ataxia 4. Mental retardation

Question 30

What are the characteristics of Prader-Willi syndrome? Include specific gene affected and imprinting pattern (not symptoms)

Answer 30

-Paternal SNRNP allele normally active, maternal allele normally silenced. -In PWS, paternal SNRNP is lost due to deletion, only silent maternal SNRNP is left -75% Caused by deletion on Q-arm of chromosome 15 -25% caused by maternal disomy (2 copies of silenced gene)

Question 31

What is locus heterogeneity?

Answer 31

A single disorder caused by mutations in genes at different chromosomal loci, however only one mutant locus is needed for the phenotype to manifest.

Question 32

What is allelic heterogeneity?

Answer 32

Different mutations at the same locus causes a similar phenotype.

Question 33

What is a common autosomal dominant disease caused by haploinsufficiency?

Answer 33

Osteogenesis imperfecta, caused by a mutation in a single allele of a gene that encodes collagen.