Chapter 23 Flashcards
What does natural selection act on and what evolves?
natural selection acts on individuals, but only populations evolve
what is genetic variation?
genetic variation among individuals is caused by differences in genes or other DNA segments
how can new genes and alleles arise?
new genes and alleles can arise by mutation or gene duplication, but sexual reproduction can result in genetic variation
how does sexual reproduction act with alleles?
sexual reproduction can shuffle existing alleles into new combinations
what is the most important in producing genetic differences?
sexual reproduction in organisms that produce sexually, more important than mutations; make adaptation possible
what does the hardy-weinberg equation test?
the hardy-weinberg equation can be used to test whether a population is evolving
what is a population?
a population is a localized group of individuals capable of interbreeding and producing fertile offspring
what does a gene pool consist of?
a gene pool consists of all the alleles for all loci in a population
when is a locus fixed?
a locus is fixed if all individuals in a population are homozygous for the same allele
what is a community?
a community is an assemblage of populations of various species living close enough for potential interaction
what is the total number of alleles for a diploid organism?
the number of individuals x 2
what is the total number of dominant alleles at a locus?
two alleles for each homozygous dominant, plus one allele for each heterozygous individual (also applies to recessive)
if there are two alleles at a locus, what is used to represent their frequencies?
p + q = 1
- frequency of alleles
if there are 320 red flowers and 160 pink flowers and 20 white flowers, how many copies of each allele, and what is the frequency?
dominant: (320 x 2) + 160 = 800
recessive: (20 x 2) + 160 = 200
P: 800/ (800+200) = .8
Q: 200/ (800+200) = .2
.8 + .2 = 1
how does hardy-weinberg suggest that a population may be evolving?
if the observed genetic makeup of the population differs from expectations under hardy-weinberg, it suggest that the population may be evolving
What is Hardy-Weinberg equilibrium?
in a population where gametes contribute to the next generation randomly and Mendelian inheritance occurs, allele and genotype frequencies remain constant from generation to generation
- describes the constant frequency of alleles in such a gene pool
what does p^2 represent?
p^2 represents homozygous dominant
what does 2pq represent?
2pq represents heterozygous
what does q^2 represent?
q^2 represents homozygous recessive
what is the quadratic and what is it used to represent?
p^2 + 2pq + q^2 = 1
- if p and q represent the relative frequencies of the only two possible alleles in a population at a particular loces
- used for frequency of genotypes
what are the five assumptions for non-evolving populations?
no mutations, random mating, no natural selection, extremely large population size (avoid genetic drift), no gene flow
what three major factors alter allele frequencies and bring about most evolutionary change?
natural selection, genetic drift, and gene flow
does random or nonrandom mating cause evolution?
nonrandom mating causes evolution, but random mating is whoever you bump into that you mate with
what can natural selection cause?
natural selection can cause adaptive evolution, which is an improvement in the match between organisms and their environment
what is genetic drift?
genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next, tends to reduce genetic variation through loss of alleles
- the smaller a sample, the greater chance of random deviation
what are the two types of genetic drift?
the founder and bottleneck effects
what is the founder effect?
occurs when a few individuals become isolated from a larger population, and the small population starts their own with their own allele frequencies
what is the bottleneck effect?
a sudden reduction in population size due to a change in the environment, the gene pool is not the original gene pool and population can become small
ex: natural disasters, earthquake,
what is gene flow?
gene flow consists of the movement of alleles among populations (fancy way of saying members between two populations mate and transfer alleles)
does gene flow reduce or increase genetic variation?
gene flow reduces genetic variation between two populations because they are ultimately sharing alleles and reducing differences
what is directional selection? what moves?
directional selection: favors individuals at one extreme end of phenotypic range
- moves either left or right
what is disruptive selection? what moves?
disruptive selection: favors individuals at both extremes of phenotypic range
- original is not favored anymore so there are 2 peaks
- the top gets pushed in and looks like an M
what is stabilizing selection? what moves?
stabilizing selection: favors intermediate variants and acts against extreme phenotypes
- reinforces the regular mean so the peak gets higher
what is sexual selection?
sexual selection is natural selection for mating success
what can sexual selection result in?
dimorphism: marked differences between the sexes in secondary sexual characteristics, males need to impress but females need to choose
what has a bigger impact, gene duplications or point mutations?
gene duplications because it brings more DNA, worst thing is insertion or deletion
intrasexual selection vs intersexual selection
intrasexual is when males compete for women
intersexual is when females are picky with their mates
intra: between one group
inter: between two groups
what does diploidy do?
diploidy maintains genetic variation in the form of recessive alleles hidden from selection in heterozygotes
when does balancing selection occur?
balancing selection occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population
- includes heterozygote advantage and frequency dependent selection
what is heterozygote advantage?
heterozygote advantage occurs when heterozygotes have a higher fitness than do both homozygotes
how does heterozygote advantage work with sickle cell?
homozygote recessive have sickle cell, homozygote dominant have no resistance, but heterozygotes can’t get malaria
