Genetic Drift, Hardy-Weinberg & Incomplete Dominance

What is evolution?

Evolution is a change in allele frequencies in a population over generations.

What is an allele?

An allele is a version of a gene.

What is allele frequency?

Allele frequency tells us how common that allele is in a population.

What are the five agents of evolutionary change?

Mutation, gene flow, genetic drift, natural selection, nonrandom mating.

What is mutation?

A change in DNA that can create a new allele.

What is gene flow?

Gene flow is the movement of alleles between populations.

What is genetic drift?

Genetic drift is when allele frequencies change because of chance.

What is natural selection?

Natural selection is when individuals with helpful inherited traits leave more offspring.

What is nonrandom mating?

Nonrandom mating means individuals are more likely to mate with certain individuals.

What is the raw source of new genetic variation?

Mutation.

Which agent results in adaptation?

Natural selection.

What is the bottleneck effect?

A population suddenly becomes much smaller, carrying only part of the original genetic variation.

What is the founder effect?

A small group starts a new population with an allele mix that may differ from the original population.

Does genetic drift affect small or large populations more?

Genetic drift affects small populations more.

What is a genotype?

The combination of alleles an individual has.

What is a phenotype?

An observable trait.

What is homozygous dominant?

Having two dominant alleles.

What is heterozygous?

Having two different alleles.

What is homozygous recessive?

Having two recessive alleles.

What is a gene pool?

All the alleles in a population.

Which genotypes show the dominant or recessive trait?

AA and Aa show the dominant trait; aa shows the recessive trait.

What does p + q = 1 mean?

It means the frequencies of the two alleles add up to 1, or 100%.

What does p² + 2pq + q² = 1 mean?

It gives the expected frequencies of the three genotypes under Hardy-Weinberg conditions.

What does p² represent?

Frequency of homozygous dominant individuals, AA.

What does 2pq represent?

Frequency of heterozygous individuals, Aa.

What does q² represent?

Frequency of homozygous recessive individuals, aa.

How do you turn a frequency into a percentage?

Multiply the decimal by 100.

How do you change a percentage into a decimal?

Divide by 100.

What if the problem gives the number of recessive individuals?

Start with q², divide by total population, take the square root to find q.

What if the problem gives the homozygous dominant frequency?

Start with p², then take the square root to find p.

What is the formula to find allele frequencies from genotype frequencies?

Use p + q = 1.

What is the frequency of AA if 64% are AA?

64%.

How do you find allele frequencies if given q?

Use p = 1 - q.

What is the frequency of allele a if q = 0.3?

0.7.

What is the frequency of heterozygotes, Aa, if p = 0.99293 and q = 0.00707?

Approximately 1.40%.

What is the frequency of aa if albinism affects 1 in every 20,000 people?

0.00005.

What percentage of plants are heterozygous if 10 out of 500 are purple?

About 24.3%.

What is the Hardy-Weinberg equilibrium?

Allele and genotype frequencies remain stable across generations.

What conditions are needed for Hardy-Weinberg equilibrium?

No mutation, no gene flow, large population, no natural selection, random mating.

What is heterozygote advantage?

When heterozygotes have greater reproductive success than either homozygous genotype.

Why can the HbS allele stay in a population?

Heterozygotes have protection against severe malaria.

What is the original source of new alleles?

Mutation.

Which agent leads to adaptation?

Natural selection.

Why does genetic drift have a greater effect in small populations?

A chance event can affect a larger portion of a small population's gene pool.

What does p² represent in Hardy-Weinberg?

AA.

What does 2pq represent in Hardy-Weinberg?

Aa.

What does q² represent in Hardy-Weinberg?

aa.

If q = 0.2, what is p?

0.8.

If 9% of a population is aa, what is q?

0.3.

If 64% of a population is AA, what is q?

0.2.

What is the frequency of the dominant phenotype if both AA and Aa show it?

p² + 2pq.

What is the frequency of brown shells predicted to be if 20% have yellow shells?

About 30.6%.

What is the frequency of yellow shells if there are 100 snails and 20 are yellow?

20%.

What is the frequency of heterozygotes if p = 0.85858 and q = 0.14142?

Approximately 24.3%.

What is the frequency of aa if q = 0.2?

4%.

What is the frequency of Aa if q = 0.3?

42%.

What is Darwin's idea of 'descent with modification'?

Living things come from earlier forms of life, with inherited traits changing over generations.

What is the principle of natural selection?

Individuals with helpful inherited traits tend to leave more offspring, making those traits more common over time.

What is the first requirement that supports evolution?

A long time span, evidenced by dating rocks and meteorites showing Earth is about 4.6 billion years old.

What evidence supports the idea of change through time in evolution?

Fossils show that organisms have changed and that environments have also changed.

What does common ancestry refer to in evolutionary biology?

Similarities in DNA and body structures indicate connections between organisms.

What does homology mean?

Similarity due to shared ancestry, such as the similar bone structure in human arms, whale flippers, and bat wings.

How is evolution defined in genetics?

As a change in the inherited characteristics of a population over generations, particularly in allele frequency.

What are the three conditions needed for natural selection to occur?

1. Variation among individuals, 2. Inheritance of traits, 3. Differences in survival and reproduction.

What is an example of natural selection in finches?

During a drought, finches with larger beaks may survive better due to access to larger seeds, leading to more offspring.

What factors influence natural selection?

The environment, including food availability, predators, climate, disease, and competition.

What does 'fitness' mean in evolutionary terms?

How successfully an organism reproduces compared to others.

What is an adaptation?

An inherited characteristic that enhances survival or reproduction in a specific environment.

What is differential reproduction?

The phenomenon where some individuals leave more offspring than others.

What is the key point about evolution and individuals?

Populations evolve over time; individuals do not.

What does adaptation not imply?

It does not mean perfection; traits have limits and trade-offs.

What is the significance of natural selection being backward-looking?

It cannot predict future needs; it acts on traits that were beneficial in past conditions.

What is an allele?

A version of a gene.

What is a genotype?

The combination of alleles an individual has.

What are homologous chromosomes?

Paired chromosomes with the same genes at corresponding locations, one from each parent.

What does homozygous dominant mean?

Having two dominant alleles (e.g., AA).

What does heterozygous mean?

Having two different alleles (e.g., Aa).

What does homozygous recessive mean?

Having two recessive alleles (e.g., aa).

What does diploid mean?

Having two sets of chromosomes, typical of most human body cells.

How many chromosome pairs do humans have?

Humans have 23 pairs, totaling 46 chromosomes.

How many alleles do we typically have for a gene?

Usually two alleles, one from each parent for a typical gene on an autosome.

What is the relationship between Darwin's ideas and natural selection?

Darwin proposed descent with modification and natural selection as key mechanisms of evolution.