Genes, Variation & Change in Populations evolution

POINT > Define gene pool, allele, and allele frequency POINT > Discriminate between single gene and polygenic traits POINT > Define the Normal Distribution POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits

POINT > Define gene pool, allele, and allele frequency A gene pool is all of the alleles present in a population Allele frequency is the number of times an allele occurs, divided by the total number in the population B allele (black) – 40% or 0.4 b allele (brown) – 60% or 0.6

WB Check: What is a gene pool? In a population of mice, suppose there are two alleles for fur length, L (long fur) and l (short fur). If half the population is homozygous dominant and half is homozygous recessive, what is the allele frequency for the “L” allele? If an invasive species kills all the long-furred mice, what is the new allele frequency for “l”?

WB Check: In a population of 100 mice, how many total alleles are there for fur length? If 50% of the above population is homozygous dominant, 25% is homozygous recessive, and 25% is heterozygous, what are the allele frequencies for the L and l alleles? “L” frequency = 0.625 “l” frequency = 0.375

POINT > Define gene pool, allele, and allele frequency Evolution occurs when there is change in the frequency of alleles in a population over time Populations evolve, not individuals!

POINT > Discriminate between single gene and polygenic traits The number of phenotypes for a trait is based on how many genes control that trait Traits controlled by a single-gene usually have only 2-3 phenotypes (like our Mendelian examples) Through natural selection, the environment causes changes in allele frequency. This changes phenotypic frequencies ex. Industrial melanism in moths

The peppered moth has these two phenotypes Industrial melanism in the peppered moth The peppered moth has these two phenotypes

Industrial melanism in the peppered moth Prior to the industrial revolution, light colored trees favored the light color moths. The frequency for the light color allele was much higher than the dark allele

Industrial melanism in the peppered moth Factory pollution killed lichen and turned tree bark brown and black in industrial areas

Industrial melanism in the peppered moth The blackened trees favored the darker moth phenotype. The frequency for the dark color allele rose in the population, while the frequency of the white allele dropped

WB Check: Which is true about industrial melanism in the peppered moth? a) Moths with the dark phenotype are healthier b) Overall allele frequencies remain constant c) Environment determines which moths are most fit d) Individual moths evolve from light color to dark

POINT > Discriminate between single gene and polygenic traits The number of different phenotypes for a trait is based on how many genes control that trait Polygenic traits are controlled by more than one gene (most traits are in this category) The environment determines fitness on the entire range causing various results and many phenotypes

POINT > Discriminate between single gene and polygenic traits The number of phenotypes for a trait is based on how many genes control that trait Polygenic traits = many phenotypes

WB Check: In species X, there is 1 gene that controls trait A and 5 genes that control trait B. Which trait would have fewer phenotypes? How many different phenotypes would you expect for trait A?

POINT > Define the Normal Distribution Normal Distribution (Bell Curve)

1. Stabilizing selection (ex. human birth weight) POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits 1. Stabilizing selection (ex. human birth weight) Large Birth Weight Small Birth Weight

1. Stabilizing selection (ex. human birth weight) POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits 1. Stabilizing selection (ex. human birth weight) Small Birth Weight Large Birth Weight

Stabilizing selection (ex. human birth weight) POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Stabilizing selection (ex. human birth weight) Large Birth Weight Small Birth Weight

Stabilizing selection (ex. human birth weight) POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Stabilizing selection (ex. human birth weight) Small Birth Weight Large Birth Weight

Stabilizing selection (ex. human birth weight) POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Stabilizing selection (ex. human birth weight) Small Birth Weight Large Birth Weight

POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Stabilizing selection: Intermediate phenotypes have higher fitness than others Small Birth Weight Large Birth Weight

Stabilizing selection leads to less variation in population POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Stabilizing selection leads to less variation in population Small Birth Weight Large Birth Weight

WB CHECK: Which phenotypes are selected for during stabilizing selection?

Directional selection (ex. Drug-resistant bacteria) POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Directional selection (ex. Drug-resistant bacteria) Low Drug Resistance High Drug Resistance

Directional selection (ex. Drug-resistant bacteria) POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Directional selection (ex. Drug-resistant bacteria) Low Drug Resistance High Drug Resistance

Directional selection (ex. Drug-resistant bacteria) POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Directional selection (ex. Drug-resistant bacteria) Low Drug Resistance High Drug Resistance

Directional selection (ex. Drug-resistant bacteria) POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Directional selection (ex. Drug-resistant bacteria) Low Drug Resistance High Drug Resistance

Directional selection (ex. Drug-resistant bacteria) POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Directional selection (ex. Drug-resistant bacteria) Low Drug Resistance High Drug Resistance

POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Directional selection (ex. Drug-resistant bacteria): one phenotypic extreme is favored Low Drug Resistance High Drug Resistance

POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Directional selection leads to change within species & potential speciation under certain circumstances (isolation) Low Drug Resistance High Drug Resistance

WB CHECK: Which phenotypes are selected for during directional selection?

Disruptive selection (Lazuli bunting coloration) Male POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Female Disruptive selection (Lazuli bunting coloration) Dull, Brown Males Bright, Blue Males

Disruptive selection (Lazuli bunting coloration) Male POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Female Disruptive selection (Lazuli bunting coloration) Dull, Brown Males Bright, Blue Males

Disruptive selection (Lazuli bunting coloration) Male POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Female Disruptive selection (Lazuli bunting coloration) Dull, Brown Males Bright, Blue Males

Disruptive selection (Lazuli bunting coloration) Male POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Female Disruptive selection (Lazuli bunting coloration) Dull, Brown Males Bright, Blue Males

Disruptive selection (Lazuli bunting coloration) Male POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Female Disruptive selection (Lazuli bunting coloration) Dull, Brown Males Bright, Blue Males

Disruptive selection (Lazuli bunting coloration) Male POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Female Disruptive selection (Lazuli bunting coloration) Dull, Brown Males Bright, Blue Males

POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Disruptive selection: Extreme individuals have higher fitness than others Dull, Brown Males Bright, Blue Males

Disruptive selection: If conditions continue, speciation may occur POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits Disruptive selection: If conditions continue, speciation may occur

WB CHECK: Which phenotypes are selected for during disruptive selection? Which type of selection would not lead to speciation? Which type of selection reduces variation?

Homework: Read pages 482-489 Assess page 486 #1-3 Workbook pages 325-328