Ch 4: Mendel and Modern evolutionary theory 1 Mendelian genetics - - PowerPoint PPT Presentation

Ch 4: Mendel and Modern evolutionary theory

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Mendelian genetics recap

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

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Alleles: variations of a gene Allele pairs determines trait Genotype determines phenotype Tt determines tall pea plants

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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

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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Mendelian traits

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

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Mendelian genetics recap

Punnett square problems

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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Variation and natural selection

Polygenic traits

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

https://news.nationalgeographic.com/2018/02/ancient-face-chedd ar-man-reconstructed-dna-spd/

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Synthetic theory of evolution

Two-stages of evolution involve variation and natural selection Stage 1: Factors produce and redistribute variation Stage 2: Natural selection acts on variation

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Causes of evolution

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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Causes of evolution

Recombination:

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

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Causes of evolution

Genetic drift: changes in allele frequencies due to chance

• large effect on smaller populations
• larger populations match true math odds

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Causes of evolution

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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Causes of evolution

Bottleneck: population shrinks and recovers

• new population reflects genetic diversity of survivors

E.g., Pingelap islanders today are mostly colorblind

• Population descend from one of three typhoon survivors
• carrier

https://youtu.be/WCKB2ZgUzsI https://www.nationalgeographic.com/photography/proof/2018/0 1/pingelap-island-colorblindness-micronesia/

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Causes of evolution

Gene flow (migration): exchange of genes between populations

• when you move you pack up 23 pairs of chromosomes and take

them with you E.g. Mutt versus purebred dogs https://www.nytimes.com/2014/08/17/magazine/should-you-fear

• the-pizzly-bear.html?smid=pl-share

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Causes of evolution

Natural selection:

• directional change relative to environmental context
• acts on variation produced and redistributed by mutations,

recombination, drift, and migration

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Anthropology example

Sickle-cell anemia: genetically inherited blood disease Mutated hemoglobin collapses red blood cells into sickles leading to anemia and death

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Anthropology example

Expect: selection against sickle-cell trait Instead: 30% some regional populations are carriers

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Anthropology example

Correlation between geographic locations with a malarial pressure and high frequencies of SCT

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Anthropology example

Geographic distribution: Mediterranean, Arabian peninsula, Southeast Asia, West Africa.

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Anthropology example

Correlation between geographic locations with a malarial pressure and high frequencies of SCT Malaria: deadly parasitic infection spread by mosquitoes Carriers for SCT have a higher survival rate for malarial infection

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