23: Genetic Inheritance

Question 1

Proband

Answer 1

First person diagnosed in a pedigree (propositus)

Question 2

Recurrence risk of an autosomal dominant trait

Answer 2

50%

Question 3

Offspring percentages when two carriers of an autosomal recessive trait mate

Answer 3

25% unaffected
50% carrier
25% affected

Question 4

Diseased allele on X in males is called what?

Answer 4

Hemiazygos

Question 5

Two ways females can have an X-liked recessive trait

Answer 5

1. Homozygous for the trait (XX)

2. Lyonization occurs

Question 6

Five examples of X-linked dominant traits

Answer 6

1. Vitamin D resistant rickets
2. Alport syndrome
3. Incontinentia pigmenti
4. Fragile X Syndrome
5. Rett Syndrome

Question 7

Structure of mito DNA

Answer 7

Double stranded, circular

Question 8

Where does mito DNA transcription occur?

Answer 8

In mito, independent of nucleus

Question 9

Introns in mito DNA

Answer 9

There are none

Question 10

Mutations in mito DNA

Answer 10

10x higher rate than nDNA, with no DNA damage repair mechanisms

Question 11

Mutational load (in terms of mito diseases)

Answer 11

The threshold of diseased mito needed to cause symptoms

Question 12

Euploidy

Answer 12

Cells with normal number of chromosomes

Question 13

Polyploidy

Answer 13

Cells contain a complete set of extra chromosomes in a cell (not compatible with human life)

Question 14

Aneuploidy

Answer 14

Cells contain missing or additional individual chromosomes (monosomy, trisomy)

Question 15

Nondisjunction

Answer 15

Abnormal separation of 1+ pairs of homologous chromosomes or sister chromatids

Question 16

Nondisjunction in germline mutation vs somatic fetal mutation

Answer 16

Germline: during meiosis: transmissible to next generation

Somatic mutation during fetal mitosis: individual will exhibit mosaicism

Question 17

Uniparental disomy (UPD)

Answer 17

Individual receives two copies of a chromosome (or part of chromosome) from one parent, and no copies from the other parent

Question 18

Effect of UPD

Answer 18

Usually no effect since most genes are not imprinted, but may result in a lack of active copies for imprinted genes

Question 19

Genomic imprinting

Answer 19

Some genes have one allele transcriptionally inactivated/methylated

Question 20

About how many human genes are known to be imprinted?

Answer 20

About 100 (mostly found in clusters)

Question 21

Do epigenetic imprints get passed on?

Answer 21

No, they only last the lifetime of that somatic cell

Question 22

Reciprocal vs Robertsonian translocations

Answer 22

Reciprocal: exchange of material between non-homologous chromosomes

Robertsonian: long arm of two acrocentric chromosomes combine, short arm is lost

Question 23

Two things gene frequencies specify

Answer 23

1. Proportion of each allele in a population

2. Proportion of each genotype in a population

Question 24

How to measure gene frequency under simple conditions and assumptions

Answer 24

Direct counting

Question 25

Hardy-Weinberg Equation

Answer 25

P^2 + 2pq +q^2 = 1

Question 26

What is Hardy Weinberg used for?

Answer 26

Estimating gene frequency using disease prevalence data

Question 27

Polygenic trait

Answer 27

Traits in which variations are thought to be caused by combined effects of multiple genes

Question 28

Multifactorial traits

Answer 28

Environmental factors cause variation in traits

Question 29

Distribution of multifactorial traits in society

Answer 29

Follow a bell shaped curve

Question 30

Liability distribution

Answer 30

For multifactorial diseases that are either present or absent, a threshold of liability must be crossed for the disease to be expressed

Question 31

Three ways recurrence risks for multifactorial diseases increase

Answer 31

1. More than 1 family member affected
2. Proband has a severe version of the disease
3. Proband is of the less commonly affected sex