Biochem 2-9 Multifactoral Inheritance & Population Genetics

Front 1

Multifactorial traits

Back 1

characteristics controlled by multiple factors, both genetic and environmental

Front 2

Polygenic inheritance

Back 2

for a trait to be controlled by multiple genes

Front 3

Pleiotropy

Back 3

for a single gene to control multiple traits

Front 4

Polymorphism

Back 4

multiple alleles in a populations for a gene

Front 5

Heritability

Back 5

estimate of how much genetics (as opposed to environment) contributes to a given trait

Front 6

Quantitative multifactorial traits

Back 6

can be assigned a numerical value (e.g. height, IQ)

Front 7

Qualitative multifactorial traits

Back 7

cannot be assigned a numerical value. They either occur or not, all or none phenomenon (e.g. heart attacks, neural tube defects).

Front 8

T/F: Polygenic and environmental factors are not mutually exclusive.

Back 8

True; Because each gene represents a different factor, polygenic traits are by definition multifactorial. At the same time there are few polygenic traits that are not influenced by multiple environmental factors, and few multifactorial traits without a genetic component, so polygenic and environmental factors are not mutually exclusive.

Front 9

Multifactorial refers to all environmental and genetic factors influencing a trait, while ______ just refers to the genetic component of a multifactorial trait.

Back 9

polygenic

Front 10

In a qualitative normal distribution (bell) curve, what do the *threshold and *incidence represent?

Back 10

The threshold is the point where the chances of developing a trait (e.g.cancer) are so high that it will occur during the person’s life. Thus, the tail of the curve above the threshold, represents the incidence, or proportion of the population that will develop that trait.

Front 11

(p+q)²=

Back 11

p2 + 2pq + q2

Front 12

Hardy Weinberg Equations:

Back 12

p2 + 2pq + q2 = 1
p + q = 1; Frequency refers to the fraction of all the alleles in the population, thus p and q add up to one. Together they constitute 100% of the alleles, e.g. if p were 0.77, then q would have to be 1 - p = 0.23.

Front 13

In Hardy Weinberg equations, p is _____ and q is _____.

Back 13

p- frequency of most abundant allele in population
q- lower allelic frequency

Front 14

Unless specifically stated otherwise, or given evidence to the contrary, assume __ represents the mutated, recessive allele, and __ is wild type, dominant form of the gene.

Back 14

q, p

Front 15

p²

Back 15

the frequency of normal individuals, usually homozygous dominants (AA)

Front 16

2pq

Back 16

the heterozygous frequency. Physicians refer to this as the carrier frequency (Aa).

Front 17

q²

Back 17

the affected frequency, usually homozygous recessive (aa). Physicians refer to this as the incidence.

Front 18

p and q are referred to as the _____ frequencies, while p2, 2pq and q2 are _____ frequencies.

Back 18

allelic, genotypic

Front 19

Hardy Weinberg primary assumption:

Back 19

population is at equilibrium, which is to say gene frequencies are constant. Note, the true definition of evolution is “any change in gene frequency,” so another way to state this assumption is that the population is not evolving.

Front 20

Hardy Weinberg secondary assumptions:

Back 20

mutation, genetic drift, migration, selection... none must be occuring

Front 21

mutation

Back 21

a change in gene sequence, usually resulting from an error in DNA replication. Note, any given mutation only adds one new allele to the population. This represents a minute change in allelic frequency, so mutation is considered a minor force driving evolution.

Front 22

genetic drift

Back 22

for a generation/s to randomly inherit a disproportionately high, or low, frequency of a particular allele. The key here is that it is a random change. Progeny just happen to inherit a higher number of the allele than you would expect. Because of the large size of most populations this is usually a negligible factor.

Front 23

migration

Back 23

emigration of a new population, with gene frequencies different from the native population, resulting in a combined population with frequencies different from either of the original populations. Intermingling and interbreeding between the two will further alter the frequencies.

Front 24

selection

Back 24

forces that influence the chance that an allele will be passed onto future generations. This is arguably the most important force in evolution. To understand selection it is necessary to define the related concept of fitness. Fitness is the ability to pass genes onto the next generation.