Lesson Overview - Enfield High Schoolenfieldhigh.sharpschool.com/UserFiles/Servers... · Lesson Overview Evolution as Genetic Change in Populations Question #4 Natural Selection A

Lesson OverviewLesson Overview17.1 Genes and Variation17.1 Genes and Variation17.1 Genes and Variation17.1 Genes and Variation

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17.2 Evolution as Genetic 17.2 Evolution as Genetic Change in PopulationsChange in Populations

Lesson OverviewLesson Overview Evolution as Genetic Change in PopulationsEvolution as Genetic Change in Populations

Question #1Natural selection : Phenotype or Genotype?

Natural selection acts directly on phenotype

Natural selection acts on an organism’s characteristics not directly on its allelesdirectly on its alleles

In any population, some individuals have phenotypes that are better-suited to their environment than are the phenotypes of other individuals

The better-suited individuals produce more offspring than the less fit individuals do


Question #2Natural Selection

(1) The mice have variations in fur color (some have white fur

(1) The mice have variations in fur color (some have white fur and some have dark fur).





(2) Hawks eat mice, and the white mice are easier to spot when flying overhead – Individuals with certain variations (dark fur) are more likely to survive (they are not seen) in their environment, passing those variations to the next generation.





(2) Hawks eat mice, and the white mice are easier to spot when flying overhead – Individuals with certain variations (dark fur) are more likely to survive (they are not seen) in their environment, passing those variations to the next generation.

(3) Over time, offspring with certain variations (dark fur) make up most of the population.


Question #3If dogs could only eat deer

Most likely, smaller dogs would die off (because they cannot obtain the food they need), and the bigger ones would survive and reproduce

After a while, instead of a population of dogs of all sizes, most of the dogs in the population would be big dogs



A

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A

The cactus has spines which keep the animals from eating it (also prevents too much water loss)

B

The cacti survive and reproduce because it has few animals eating it. The offspring also have spines that protect them, allowing them to mature, and eventually reproduce


Question #5What is a gene pool?

All of the genes, including all the different alleles for each gene, that are present in a population


Question #6What is allele frequency?

The number of times an allele occurs in a gene pool compared to the total number of alleles in that gene pool for the same gene

The percent of a specific allele


Question #7Define evolution in genetic terms

A change in the frequency of alleles in a population over time


Question #8Do populations or individuals evolve? Explain.

Populations evolve

Natural selection operates on individual organisms, but the changes it causes in allele frequency show up in the changes it causes in allele frequency show up in the population as a whole

If an organism has a phenotype that is poorly adapted to its environment, the organism may be unable to survive and reproduce – however, within its lifetime, it cannot evolve a new phenotype in response to its environment


Question #9Three main sources of genetic variation

Mutations� A mutation is any change in the genetic material of a cell (some

mutations will affect the fitness of the organism)

� Mutations matter in evolution only if they can be passed from generation

to generation (occur in the germ line cells)to generation (occur in the germ line cells)

Genetic Recombination� This occurs during sexual reproduction based on how the chromosomes

line up during meiosis and also from crossing over

Lateral Gene Transfer� The passing of genes from one individual to another, or even from

individuals of one species to another, that is not its offspring (organsims

pick up “new” genes)


Question #10Range of phenotypes for single-gene vs. polygenic traits

Single-gene traits have just a few distinct phenotypes

Polygenic traits have many possible phenotypes, which often are not clearly distinct from one anotherare not clearly distinct from one another


Question #11Student Heights

A = What is the average height for this population?A = What is the average height for this population?

The average height for this population is 170 – 179 cm

B = Jane and Miguel are both 172 cm tall. Does that mean they have the same genotype? Why or why not?

No – because height is a polygenic trait, there are many different combinations of alleles that result in the same height


Question #12How does natural selection affect single-gene traits?

Natural selection on single-gene traits can lead to changes in allele frequencies and, thus, to changes in phenotype frequencies


Question #13How does natural selection affect polygenic traits?

Natural selection on polygenic traits can affect the relative fitness of phenotypes and thereby produce one of three types of selection: directional, stabilizing, or disruptive selectionselection


Question #14Directional Selection

When individuals at one end of the curve have higher fitness than individuals in the middle or at the other end of the curve


Question #15Stabilizing Selection

When individuals near the center of the curve have higher fitness than individuals at either end of the curve


Question #16Disruptive Selection

When individuals at the outer ends of the curve have higher fitness than individuals near the middle of the curve


Question #17What is genetic drift?

The random change in allele frequency caused by a series of chance occurrences that cause an allele to become more or less common in a population

Another source of evolutionary change


Question #18Bottleneck Effect and the Founder Effect

Both are forms of genetic drift (both are random changes in allele frequency of a population)

The bottleneck effect is genetic drift following a dramatic The bottleneck effect is genetic drift following a dramatic reduction in the size of a population

The founder effect is genetic drift as a result of the migration of a small subgroup of a population


Question #19Genetic Equilibrium

Situation in which allele frequencies in a population remain the same

Genetic equilibrium can be disrupted by…Genetic equilibrium can be disrupted by…

� Nonrandom mating (certain traits will be selected for)

� Small population size (greatly affected by genetic drift)

� Immigration or emigration

� Mutations

� Natural selection

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Lesson Overview - Enfield High Schoolenfieldhigh.sharpschool.com/UserFiles/Servers... · Lesson Overview Evolution as Genetic Change in Populations Question #4 Natural Selection A