ZR

Lecture 7 Slides - Genetics and Evolution(1)

Course Overview

  • Course Code: 4PSYC003W

  • Title: Biological Psychology

Lecture Plan

  1. Genetics

    • a) DNA

    • b) Chromosomes

    • c) Genes and alleles

  2. Evolutionary Theory

    • a) Genetic variation

    • b) Natural selection

    • c) Differential survival and reproduction

    • d) Sexual selection

  3. Human Evolution

    • a) Emergence of hominids

    • b) From hominids to humans

    • c) Key developmental stages

Key Terms

  • Genetics: Study of heredity and how traits are transmitted across generations.

  • Inheritance: Biological process of transmitting genetic material from parents to offspring.

  • Genome: Total hereditary (genetic) information contained in an organism's cells.

Structure of DNA

  • Consists of:

    • Phosphate, Deoxyribose sugar, Nitrogenous bases (A, T, C, G)

  • Double Helix Structure:

    • Base pairs: A-T and C-G

    • Codon: Three base pairs coding for a single amino acid.

Structure of Chromosomes

  • Chromosomes formed through supercoiling of DNA around histones to form nucleosomes.

  • Structure allows efficient packaging of genetic material in the nucleus.

Human Karyotype

  • Karyotype: Total set of chromosomes in a species.

  • Humans have 46 chromosomes (23 pairs). Includes:

    • 22 autosome pairs

    • 1 sex chromosome pair (XX for females; XY for males).

Alleles and Gene Locus

  • Gene Locus: Specific position on a chromosome for a gene.

  • Alleles: Variants of a gene at the same locus.

    • Example: loci for eye color (blue, brown).

Crossing-over and Recombination in Meiosis

  • Gamete production: Meiosis results in 4 haploid cells from one diploid cell.

  • Involves the exchange of genetic material between homologous chromosomes, leading to genetic diversity.

How Genes Code for Proteins

  • Genes encode chemical structures for protein synthesis.

  • Human characteristics are often polygenic (influenced by multiple genes).

  • The relationship between genes and behaviors is complex due to environmental influences.

Evolution

  • Definition: Changes in allele frequencies in populations over time, favoring adaptive traits.

  • Notable figures:

    • Charles Darwin: Formulated natural selection theory.

    • Alfred Russel Wallace: Developed a similar theory independently.

Components of Natural Selection

  1. Genetic Variation: Differences among individuals in a population.

  2. Inheritance: Some traits are hereditary; others are influenced by the environment.

  3. High Rate of Population Growth: Leads to competition for resources.

  4. Differential Survival and Reproduction: Traits that confer advantages lead to greater reproductive success.

Sources of Genetic Variation

  • Mutation: Random gene changes.

  • Gene Flow: Transfer of genes between populations.

  • Genetic Drift: Changes in allele frequency due to random sampling.

  • Sexual Reproduction: Shuffling of genetic information during gamete formation.

Types of Variation

  • Discontinuous Variation: Controlled by a single gene; distinct categories (e.g., blood type).

  • Continuous Variation: Controlled by multiple genes; quantitative traits (e.g., height).

Natural Selection Types

  1. Stabilizing Selection: Preference for average traits.

  2. Directional Selection: Favoring traits at one end of the range.

  3. Disruptive Selection: Favoring traits at both extremes over average traits.

Examples of Selection

  • Stabilizing Selection: Traits beneficial for survival such as those in specific species (e.g., Cheetahs).

  • Disruptive Selection: Variations in traits within species (e.g., tortoises).

Differential Survival and Reproduction

  • Example: The peppered moth illustrates natural pigmentation advantages in varying environments.

Sexual Selection

  • Traits enhancing reproduction may not affect survival but can influence mate choice (e.g., peacock tails).

Human Evolution Timeline

  • Earliest human ancestors appear approx. 5 million years ago.

  • Timeline in a 24-hour format:

    • Earliest Homo sapiens at 23:59:56 (300-150 ka ago).

The Evolution of Humans and Primates

  • Major evolutionary milestones involving species like:

    • Chimpanzee, Bonobo, and Homo species.

Emergence of Hominids

  • Australopithecus: Key characteristics include bipedalism and tool use.

Evolutionary Forces

  • Significant changes in human behavior occurred during the Pleistocene (2.6 Ma - 11.7 ka ago).

Brain Evolution Across Species

  • Brain size progressively increased from Australopithecus to Homo sapiens:

    • Australopithecus ~450cc, Homo erectus ~1000cc, Homo sapiens ~1600cc.

Major Homo Species

  • Homo habilis: First toolmaker (2 Ma ago).

  • Homo erectus: Migrated from Africa; sophisticated tool use (1.3 Ma ago).

  • Homo heidelbergensis: Direct ancestor theory with Neanderthals.

  • Homo neanderthalensis: Coexisted with early Homo sapiens.

  • Homo sapiens: Evidence of advanced tools, art, and eventual migration from Africa (300 ka ago).

References

  • Darwin & Wallace (1858): "On the Tendency of Species..."

  • Darwin (1859): "On the Origin of Species..."

  • Additional literature on genetics and evolution.