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.