Population Genetics and Natural Selection - Genetics 4

Question 1

Population genetics

Answer 1

The study of allele frequencies within a population and how these frequencies may change over time.

Question 2

Allele

Answer 2

Distinct variants of a specific gene.

Question 3

Wild type

Answer 3

Version of a gene that is the most common in a population and functions normally. These tend to be dominant, but there are exceptions.

Question 4

Mutant alleles

Answer 4

Version of a gene that differs from the standard/wild type allele. Tends to be recessive, but there are exceptions.

Question 5

Why does allele frequency in a population fluctuate over time?

Answer 5

Alleles can be in competition so their distribution/prrevalence changes with selection pressure over time. Similar to flucuation in antibiotic resistance in bacteria.

Question 6

Dominant allele

Answer 6

An allele that produces the same phenotype whether it is present with the same allele in a diploid organism (homozygous) or a different allele (heterozygous).

Question 7

Recessive allele

Answer 7

An allele that produces its distinctive phenotype only when present with the same allele in a diploid organism (homozygous).

Question 8

Diploid organisms

Answer 8

Organisms that have 2 alleles of each gene.

Question 9

Wild type

Answer 9

The typical form of a gene, which is usually dominant.

Question 10

Mutant

Answer 10

An alternative form of a gene that is usually recessive.

Question 11

Ageing gene in C.elegans

Answer 11

Age-1: gene involved in ageing and lifespan.

Question 12

Allele frequency

Answer 12

The proportion of a specific allele among all allele copies in a population.

Question 13

Determinining Allele frequencies from genotype frequency

Answer 13

(2 x homo D/R) + ( 1 x hetero) / 2 x total population

Question 14

Why do we multiply the homozygous frequencies and total population by 2 when determinining Allele frequencies from genotype frequency

Answer 14

Because each individual has 2 alleles in the total population and if they have homozygous alleles, they have 2 of each.

Question 15

Hardy-Weinberg principle

Answer 15

A principle that states allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.

Question 16

Hardy-Weinburg equation

Answer 16

p2 + 2pq + q2 = 1
p + q = 1
p2 = AA
2pq = Aa
q2 = aa

Question 17

Hardy-Weinberg assumptions

Answer 17

• Only sexually reproducing diploid organisms
• No mutation or ongoing evolution of the alleles
• No genetic drift
• Random mating
• No gene flow in/out of the population.

Question 18

Natural selection

Answer 18

The process by which organisms better adapted to their environment tend to survive and produce more offspring.

Question 19

Requirements for natural selection

Answer 19

• Genetic variation in population
• Variation must affect survival or reproductive success
• Stable environment

Question 20

Benefit of a stable environment for natural selection

Answer 20

Maintains the alleles that will be selected for

Question 21

Fitness

Answer 21

Likelihood to survive and reproduce.

Question 22

Absolute fitness

Answer 22

Fitness of an individual.

Question 23

Relative fitness

Answer 23

Fitness of individuals with a particular genotype relative to other genotypes.

Question 24

Stabalising selection

Answer 24

A type of natural selection where variation is reduced if individuals close to the mean (least extreme traits) have the highest fitness. So the allele frequency graph gets longer and more narrow

Question 25

Directional selection

Answer 25

A type of natural selection where individuals at one extreme have the highest fitness so the graph stays the same shape but moves in direction of favoured allele which increases in freqiency while the disfavoured allele decreases in frequency.

Question 26

Disruptive Selection

Answer 26

A type of natural selection where individuals at either extreme have highest fitness, maintaining and increasing the high frequencies of the two sets of alleles, while the mean alleles decrease in freqiency. Eventually the population splits in two

Question 27

Type of Natural selection that is a key driving force in phenotypic variation, sexual dimorphism and even speciation.

Answer 27

Disruptive speciation

Question 28

Genetic drift

Answer 28

Random events leading to survival/death of random genotypes that aren’t linked to adaptation or fitness. It has the power to profoundly alter allele frequency, especially in small populations.

Question 29

Population bottlenecks

Answer 29

A large population declines and the gene pool of the reduced population does not represent the original population.

Depiction of how genetic bottleneck decreases genetic variation in a population

Question 30

Causes of genetic bottlenecks

Answer 30

Huge environmental change:
* Radiation population
* Overhunting
* Volcanic eruption

Question 31

Founder effects

Answer 31

A few individuals colonize a new location, and their gene pool is not representative of the original location. The smaller population can increase frequency of usually detrimental or less common alleles, so the gene pool is smaller.

Question 32

Tay-Sachs Disease

Answer 32

An autosomal recessive disease caused by mutations in the HEXA gene, leading to progressive nerve damage and unlikely to live beyond 4 years. At-risk populations can have genetic “carrier screening” . Pre-implantation genetic screening is common place for carrier couples.

Question 33

Would the HEXA gene be in the Hardy-Weinberg equilibrium?

Answer 33

NO
* Many mutations = different alleles
* Gene flow outside of the prevalent populations
* Non-random mating as homozygotes die young and peope get genetic screening to not mate with other carriers

Question 34

HEXA gene

Answer 34

Gene associated with Tay-Sachs Disease, with over 100 mutations identified.

Question 35

Non-random mating

Answer 35

A mating system where the likelihood of two genotypes or phenotypes breeding is not determined by their population frequencies

Question 36

Assortative mating

Answer 36

A type of non-random mating where mates chosen based on genotype/phenotype.

Question 37

Positive assortative mating

Answer 37

Mates are chosen based on similar genotype/phenotype.

Question 38

Negative assortative mating

Answer 38

Mates are chosen based on dissimilar genotype/phenotype.

Question 39

Major Histocompatibility Complex (MHC)

Answer 39

A set of molecules displayed on cell surfaces that are crucial for the immune system to recognize foreign molecules. They are encoded for by highly polymorphic HLA genes. There is evidence of negative assortative mating in humans for MHC genes.

Question 40

Runaway Theory

Answer 40

A theory suggesting that certain traits become more exaggerated over time due to female preference (sexual selection)

Question 41

How does natural selection impact mate choice?

Answer 41

Natural selection selects beneficial traits. Females notice this, so selection for females with this preference occurs, eventually leading to an exaggeration of the trait

Question 42

Where does direction of mate choice come from?

Answer 42

The sex with more to lose.
* Higher energy investment in producing the gamete
* Higher energy investment in caring for the ffspring
* Lower number of thier gametes than other sex

Question 43

Why is there an optimal tail length for male birds in this example?

Runaway Theory

Answer 43

As tails get longer due to mate selection (males with long tails mate and pass on the genes) it is detrimental to survival. This could be due to higher risk of predation. Therefore there is an optimal tail length

Question 44

Handicap Principle

Answer 44

A theory that suggests that costly traits are reliable signals of fitness.

Question 45

Darwin’s Theory of Natural Selection

Answer 45

The theory that evolution occurs through the process of natural selection, where organisms better adapted to their environment tend to survive and reproduce.

Question 46

Genotype

Answer 46

The genetic constitution of an individual.

Question 47

Phenotype

Answer 47

The observable characteristics or traits of an individual.

Question 48

Genotype frequency

Answer 48

The proportion of a specific genotype among all individuals in a population.

Question 49

Phenotype frequency

Answer 49

The proportion of a specific phenotype among all individuals in a population.