Chapter 19 Flashcards
what is a gene?
a segment of DNA that codes for a phenotype
what is an allele?
different versions of a particular gene
what is a genotype?
the 2 alleles that define a phenotype
what is a phenotype?
physical representation of a genotype
what does homozygous mean?
alleles for a genotype are the same
what does heterozygous mean?
alleles for a genotype are different
what is the hardy-weinberg principle?
the original proportions of the genotypes in a population will remain constant from generation to generation as long as five assumptions are met
what are the five assumptions that must be met for hardy-weinberg?
- no mutation: DNA not changing
- no gene flow: no population mixing
- random mating
- large population size
- no natural selection
what must the frequencies of alleles always equal, whether the population is in HW equilbrium or not?
1, so homozygous dominant + heterozygous + homozygous recessive = 1
a population NOT in HW equilibrium indicates that one or more of the 5 evolutionary agents are operating in a population. list those 5 agents
- DNA mutation
- gene flow occurring
- mates chosen
- small population
- natural selection
what is the ultimate source for variation?
mutation
why isn’t mutation a strong evolutionary driver?
it happens too rarely
what is one of the most potent agents of change?
gene flow
does gene flow occur because of seasonal migration?
no because
- movement of the entire population
- not during a reproductive period
what is nonrandom mating?
mating with specific genotypes
what are the 2 types of nonrandom mating?
- assortative mating
2. disassortative mating
what is assortative mating?
between phenotypically similar individuals, increasing homozygotes
what are the 2 kinds of assortative mating?
- inbreeding
2. self-fertilization
what is dissasortative mating?
between phenotypically different individuals, produces excess of heterozygotes
what is the only evolutionary agent that produces adaptive evolutionary changes?
natural selection!
what is natural selection?
environmental conditions determine which individuals in a population produce the most offspring
what are the 3 conditions for natural selection to occur? (basically Darwin’s 3 postulates)
- variation must exist among individuals
- variation must result in differential survival of offspring
- variation must be genetically inherited
is natural selection evolution?
NOOOOO
how is natural selection not evolution?
it is a process by which change (evolution) MAY occur over time but it does NOT always have an evolutionary result
what is artificial selection?
a breeder selects for desired characteristics
will the offspring between different dog breeds be considered hybrids? why or why not?
no, because all dog breeds are the same species, capable of producing viable offspring = NOT hybrids
what is the problem with small populations?
genetic drift
what is genetic drift?
when frequencies of particular alleles may change by chance alone, very random
what are the 2 kinds of genetic drift?
- founder effect
2. bottleneck effect
what is the founder effect?
when a small group is isolated or displaced from the original population, form a new population with a small allelic pool; like the Amish
what is the bottleneck effect?
a sudden, drastic reduction in population and gene pool size, like from a natural disaster, disease, or decreased prey
what is fitness?
a phenotype with greater fitness usually increases in frequency; most fit is given a value of 1
what 3 things is fitness of combination of?
- survival: how long an organism lives
- mating success: how often the organism mates
- number of offspring per mating that survive
what are the 3 types of selection acting on traits affected by multiple genes?
- directional
- stabilizing
- disruptive
what is disruptive (diversifying) selection?
acts to eliminate intermediate types, left with extremes= bimodal distribution
give an example of disruptive selection
predation and food pressures on body size;
smaller means less food required and can hide
larger can gather more food and get away from predators
what is directional selection?
acts to eliminate one extreme from an array of phenotypes
give an example of directional selection
Darwin’s finches’ beaks changing with climate
what is stabilizing selection?
acts to eliminate both extreme phenotypes; favors intermediates; distribution gets narrower
give an example of stabilizing selection
birthweight in humans
what is oscillating selection? give an example
one phenotype favored at a time, another phenotype favored at another; moth colors in the UK before, during, and after the industrial revolution
what is frequency dependent selection?
favors phenotypes that are either common (positive frequency dependent selection) or rare (negative frequency dependent selection)
does positive or negative FD selection increase or decrease variation?
look in book to answer
what is sexual dimorphism?
high degree of differences in outward appearance of females and males
why do females tend to have a greater investment in producing offspring?
they evaluate male secondary sexual characteristics to choose which potential mate has “better” genes
can more than one evolutionary agent be present in a population? if so, what are the results of such interactions?
yes, and it means evolution is not a guarantee; it takes a long time
does evolution have a purpose?
no, it is not changing a population into a preconceived ideal
what is the only evolutionary agent that is adaptive and results in a more fit population?
NATURAL SELECTION
what can gene flow and genetic drift actually do to a population’s fitness?
may actually decrease it
