Ch 4: Mendel and Modern evolutionary theory

Week 4(Ch 3/4)

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-Anthro club

-Social sciences night

-Quiz Thursday, October 4th

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Mendel's principles of inheritance

Synthetic theory of evolution

Homework pass back

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Mendelian principles of inheritanceMendel's principles explains transmission of traits generation to generation

Background: decades of experiments with pea plant hybrids.

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Mendelian principles of inheritance

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Experiments: crossbred pure-bred pea plants

Parent generation:-tall pea plants x short pea plants

F1 generation:

F2 generation:

Mendel's first principle of inheritancePrinciple of segregation: traits are controlled by discrete units which come in pairs and separate into sex cells.

Alleles: variations of a gene at a locus, i.e., allele pairs control trait expression

E.g., pea plant height is controlled by two alleles at one locus

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Mendel's first principle of inheritanceRecessive alleles are masked by the expression of dominant alleles

Homozygous: two copies of an allele

Heterozygous: two different alleles

Genotype: organism's entire genetic makeup

Phenotype: observed physical expression of genotype/genes

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Mendel's second principle of inheritancePrinciple of independent assortment: traits are inherited separately

E.g., pea plant height and seed color are not inherited together

-genes that code for different traits sort out individually during gamete formation

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Punnett square problems1. Identify the different phenotypic and genotypic ratios in F2 generations for a cross of two heterozygous tall plants (tall = dominant trait).

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Punnett square problems2. Hypothetically, B is the allele that causes brachydactyly. If a man with two normal alleles (bb) has average length fingers/toes has kids with a woman with brachydactyly (Bb).

What proportion of their kids will have average length fingers/toes?

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Synthetic theory of evolutionSynthetic theory of evolution

-modern synthesis of Darwin's theory and genetics now:

Evolution defined: change in allele frequencies of a population from one generation to the next.

Gene pool: the genetic material (alleles) making up a population of organisms

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Mendelian geneticsMendelian traits-discrete traits-one gene determines one trait-rarely influenced by environment

Polygenic traits-continuous-multiple genes determine one trait-relationship between genetics/environment heavily influential

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Synthetic theory of evolutionTwo-stages of evolution involve variation and natural selection

Stage 1: Factors produce and redistribute variation

Stage 2: Natural selection acts on variation

Microevolution: changes from generation to generation

Macroevolution: speciation, changes over time evident in the fossil record

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Factors producing and redistributing variation1. Mutations: any change in alleles-produces new alleles (only source of new genetic material)-only passed on if occurs in gametes

2. Recombination: chromosome pairs exchange DNA during meiosis shuffling variation for natural selection to act on

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Factors producing and redistributing variation3. Genetic drift: changes in allele frequencies due to chance

Founder effect: small subpopulation starts new popn

Bottleneck: population shrinks and recoversE.g., Pingelap islanders today are mostly colorblind

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Factors producing and redistributing variation4. Gene flow: (migration) exchange of genes between populationsE.g., significant gene flow between human populations explains the low occurrence of hominin speciation in the past million years

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Variation and natural selectionNatural selection

-directional change relative to environment

-acts on variation

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