Chapter 23 Flashcards
Microevolution
A change in allele frequencies in a population over generations
Selection acts on __________, causing populations to evolve
individuals
Genetic variation is money in the bank for _________
evolution
_________ can cause the genome to change
mutations
Sexual reproduction
can result in genetic variation by recombining existing alleles
The Hardy-Weinberg Equation
p² + 2pq + q² = 1
p + q = 1
This is a model
Model
An intentional simplification of a complex situation designed to eliminate extraneous detail in order to focus attention on the essentials of a situation
Conditions for Hardy Weinberg
1) No mutations
2) Random Mating
3) No natural selection
4) large population size
5) No gene flow
Relative fitness
the contribution an individual makes to the gene pool (more offspring, more fitness)
T/F: New genes and alleles can arise from mutations and gene duplication
True
T/F: Chromosomal mutations that delete, disrupt, or rearrange many loci are typically beneficial
False - they are typically harmful
Population
A localized group of individuals capable of interbreeding and producing fertile offspring
T/F: the gene pool consists of all the alleles in an individual
False - it consists of all the alleles in a population
Natural Selection
increases the frequency of alleles that enhance survival and reproduction; involves both chance and sorting
Genetic drift
describes how allele frequencies fluctuate unpredictably from one generation to the next; different genotypes in a small population owing to the chance disappearance of particular genes as some die or do not reproduce
Gene Flow
consists of the movement of alleles among populations; reduces variation; can be transferred by fertile individuals or gametes
Founder event
occurs when one or a few individuals become isolated from a larger population
Population bottleneck
a sudden reduction in population size due to a change in the environment
Effects of genetic drift
1) GD has more effect in small populations
2) GD can cause allele frequencies to change at random
3) GD can lead to a loss of genetic variation in a population
4) GD can cause harmful alleles to become fixed
Modes of selection
1) Directional
2) Stabilizing
3) Disruptive
4) Sexual
5) Balancing
6) Frequency-dependent
7) Heterozygote advantage
Directional Selection
favors individuals at one
extreme end of the phenotypic range
Stabilizing Selection
favors intermediate variants
and acts against extreme phenotypes
Disruptive Selection
favors individuals at both
extremes of the phenotypic range
T/F: Only natural selection can cause adaptive evolution. All other selections just change allele frequency
True
Sexual Selection
natural selection for mating success
Sexual Dimorphism
marked differences between the sexes in secondary sexual characteristics
Balancing Selection
occurs when natural
selection maintains stable frequencies of two or
more phenotypic forms in a population
Frequency-dependent selection
the fitness of a phenotype declines if it becomes too common in the population
Heterozygote advantage
heterozygous individuals have a higher chance of survival than homozygous individuals
Intrasexual selection
Direct competition among individuals of one sex (Often males) for mates of the opposite sex
Intersexual selection
often called mate choice; occurs when individuals of one sex (usually females) are choosy in selecting their mates
