Mendelian genetics recap Principle of segregation: traits are - - PowerPoint PPT Presentation

Mendelian genetics recap

Principle of segregation: traits are controlled by discrete units which come in pairs and separate into sex cells. Principle of independent assortment: traits are inherited separately

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Alleles: variations of a gene Allele pair determines trait Genotype determines phenotype Tt determines tall pea plants XY determines biological sex

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Mendelian genetics recap

Dominant alleles mask the expression of recessive alleles. Homozygous: allele pairs (TT or tt or XX) Heterozygous: alleles pairs (Tt or XY)

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Mendelian genetics recap

Punnett square problem

Hypothetically, the B allele causes brachydactyly while b alleles cause normal finger length. A man with normal finger length has kids with a woman with brachydactyly (Bb).

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Mendelian traits

• discrete traits
• one gene determines one trait
• rarely influenced by environment

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Types of traits

Polygenic traits

• continuous
• multiple genes determine one trait
• relationship between genetics/environment heavily influential

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Synthetic theory of evolution

Synthesis of Darwin’s theory and Mendelian genetics into modern evolutionary biology Evolution definition: change in the allele frequencies of a population from one generation to the next. Two-stages of evolution involve variation and natural selection Stage 1: processes produce and redistribute variation Stage 2: Natural selection acts on variation

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Processes of evolution: mutation

Mutations: any change in alleles

• produces new alleles (only source of new genetic material)
• only passed on if occurs in gametes

E.g., sickle-cell anemia due to point mutation (changes in a single nucleotide base).

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Processes of evolution: recomb

Recombination:

• chromosome pairs exchange DNA during meiosis
• greater genetic diversity for natural selection to act on

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Processes of evolution: genetic drift

Genetic drift: changes in allele frequencies due to chance

• large effect on smaller populations

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Processes of evolution: genetic drift

Examples of drift: Founder effect: small subpopulation leaves to find new population E.g., polydactyly in Amish communities

• founders/immediate descendants = carriers
• homozygous recessive individuals emerged in

gene pool

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Processes of evolution: genetic drift

Examples of drift: Bottleneck: population shrinks and recovers

• new population reflects genetic diversity of survivors

E.g., 60% Pingelap islanders are colorblind

• Population descend from a single survivor of a typhoon
• carrier

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Processes of evolution: gene flow

Gene flow (migration): gene exchange between populations E.g. Mutt versus purebred dogs

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Stage two

Natural selection: directional change in allele frequencies relative to environmental context

• acts on variation produced and redistributed by mutations,

recombination, drift, and migration

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Anthropology example

Normal dominant allele = HbA Mutated recessive allele = HbS Mutated hemoglobin collapses red blood cells into sickles leading to anemia and death

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Anthropology example

Expect: selection against HbS (sickle-cell allele) because it causes anemia Instead: 30% population have the sickle-cell allele in some areas

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Anthropology example

Malaria: deadly parasitic infection spread by mosquitoes Correlation: regions malarial pressure and high HbS allele frequencies

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Regions of note Mediterranean, Arabian peninsula, Southeast Asia, W. Africa Biocultural evolution example Agriculture: deforestation and standing water

• mosquito breeding areas overlap with human settlements

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