Genetic drift (two types) Genetic drift: changes in allele - - PowerPoint PPT Presentation

Genetic drift (two types)

Genetic drift: changes in allele frequencies due to chance. Founder effect Ex: Polydactyly in Amish communities

• Small gene pool means rarer genes are inherited

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Genetic drift (two types)

Genetic bottleneck: population shrinks to only a few people. Ex: Pingelap islanders are mostly colorblind.

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Gene flow (migration)

Gene flow: Exchange of genes between populations.

• AKA migration

Ex: Low occurrence of hominin speciation in the past million years explained by migration.

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Natural selection

• Acts on variation produced and redistributed

by mutations, recombination, genetic drift, and gene flow.

• Differential reproductive success relative to

the environment.

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Anthropology example: Sickle-cell anemia

• Lethal, genetically inherited blood disease.
• The phenotype of a mutated hemoglobin allele
• Collapses red blood cells into sickles

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Sickle-cell trait: Natural selection in humans

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Expect: Selection against sickle-cell allele. Instead: 30% some regional populations are carriers.

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Anthropology example: Sickle-cell anemia

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

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Anthropology example: Sickle-cell anemia

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

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Anthropology example: Sickle-cell anemia

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Anthropology example: Sickle-cell anemia

Macroevolution

Classification

Kingdom: Animalia Phyla: Chordata Class: Mammalia Order: Primate Family: Hominidae Genus: Homo Species: sapiens

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Classifying biology

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Question: Based on physical traits alone, which is the most similar?

• Classification based on evolutionary relationships

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Homologies

Homologies: similarities between groups due to common descent. Ex: birds, bats, mice, crocs all have four limbs Contrast with analogies: similarities due to common function

Two types of homologies

Ancestral traits: similarities in many taxonomic groups inherited from a remote ancestor. Derived traits: modified from the ancestral conditions.

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Schools of classification

Evolutionary systematics: hypothesizes about ancestor-descendant relationships over time

• Make phylogenetic trees

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Schools of classification

Cladistics: use shared derived traits to identify new species Clades: lineages sharing a common ancestor.