Q&A: Modes of Inheritance I

Flashcards covering Modes of Inheritance I, population genetics, Hardy-Weinberg equilibrium, genetic drift, pedigree analysis, and Mendelian inheritance patterns.

What is the definition of a species in genetics?

A group of organisms comprised of similar individuals capable of interbreeding.

How is a population defined in population genetics?

Individuals of a particular species occupying a definite space, in which individuals interact, interbreed, and exchange genetic material.

What constitutes a gene pool?

All alleles from all individuals within a population.

What is population genetics?

The quantitative study of the distribution of allele frequencies in a population and its changes over time and between populations.

What does the Hardy-Weinberg law state?

Allele frequencies remain constant over time in a population that does NOT evolve (genetic equilibrium).

What is the Hardy-Weinberg equation for genotype frequencies at a locus with two alleles?

$$(p+q)^2 = p^2 + 2pq + q^2 = 1$$

In a sample population of 25 mice containing 12 Bb, 4 BB, and 9 bb, what is the formula to calculate the brown allele frequency $q$?

$$q = \frac{(bb \text{ mice} \times 2) + (Bb \text{ mice} \times 1)}{\text{total mice} \times 2}$$

To which chromosomes or sexes does the Hardy-Weinberg principle NOT apply?

It does NOT apply to the X-chromosome in males.

What five main factors disturb Hardy-Weinberg equilibrium?

1. Non-random mating
2. Small population size
3. Mutations
4. Natural selection
5. Immigration and emigration

What effect does population stratification have on genotype frequencies?

It leads to an apparent excess of homozygotes in the overall population without affecting the frequency of autosomal dominant disease.

What is consanguinity?

Mating between related individuals (parents sharing a common ancestor).

What is the incidence rate of Tay-Sachs disease in the Ashkenazi Jew population compared to the general population?

1:3600 in the Ashkenazi Jew population compared to 1:360000 in the general population.

How is genetic fitness ($f$) defined?

A measure of surviving affected offspring compared to control, determined by the collaboration between survival and fertility.

What does a genetic fitness value of $f = 0$ indicate?

The mutant allele causes death or sterility, or is completely selected against negatively.

What is gene flow?

The slow diffusion of genes through geographic or social barriers involving large populations.

In which geographic region is the CCR5 mutation found at its highest frequency according to gene flow observations?

Europe (it is small in the Middle East and India, and almost absent in Africa).

Which two main factors influence differences in allele frequencies among different ethnic groups?

Genetic drift and heterozygote advantage.

What is genetic drift?

A random change in allele frequency in small populations due to chance rather than natural selection.

What are the two specific types of genetic drift described in population genetics?

Founder effect and bottleneck event.

What is the founder effect?

Genetic drift that occurs after a few individuals (a fraction of the original gene pool) start a new population in isolation.

What is a bottleneck effect?

Genetic drift occurring after a critical event drastically reduces population size, altering allele and genotype frequencies.

What is heterozygote advantage?

A situation where heterozygous individuals have increased genetic fitness compared to wild-type homozygotes.

Which disease provides a classic example of heterozygote advantage against malaria in Africa?

Sickle cell anemia.

What is pleiotropy?

When a single abnormal gene produces a variety of phenotypes in different organs, with different signs and symptoms, at different times.

What is reduced or incomplete penetrance?

When an individual carries a mutant genotype but fails to express the corresponding phenotypic trait.

What is variable expressivity?

Variation in the severity of phenotypic symptoms among individuals sharing the same mutated genotype.

What is a proband in a pedigree?

The first individual in a family who is diagnosed with a genetic disease (also termed propositus/a or index case).

When interpreting a pedigree, what sex distribution suggests an autosomal inheritance pattern?

An approximately equal (50:50) ratio of affected males to affected females.

Which inheritance observation in a pedigree definitively rules out X-linked inheritance?

Male-to-male transmission.

What proportion of all Mendelian disorders exhibit autosomal dominant inheritance?

More than 50% (>50%).

What are three examples of autosomal dominant disorders?

Huntington's disease, polycystic kidney disease, and familial hypercholesterolemia.

What is the recurrence risk for each child born to an autosomal dominant heterozygous parent?

50%.

What functional types of proteins are usually mutated in autosomal dominant disorders?

Structural proteins or transcription factors.

What are five examples of autosomal recessive disorders?

Albinism, phenylketonuria, alkaptonuria, sickle cell anemia, and cystic fibrosis.

What is the recurrence risk for offspring when two carrier parents (heterozygotes) of an autosomal recessive disease mate?

25%.

What types of proteins are mostly affected in autosomal recessive disorders?

Enzymes.

How is Y-linked trait inheritance characterized?

It is transmitted strictly from father to son across all generations, affecting males only.

What are three examples of X-linked recessive disorders?

Hemophilia A, Duchenne muscular dystrophy, and colorblindness.

What proportion of daughters born to a father affected by an X-linked recessive disorder will be carriers?

100% of daughters.

In X-linked dominant inheritance, what are the phenotypic proportions of children born to an affected mother and a normal father?

1/2 (50%) of sons and 1/2 (50%) of daughters are affected.