3.1 Biological Psychology: Genetic Code

Introduction to Biological Psychology

• Series Overview

  • Focus on biological psychology, genetics, behavior, brain cells (neurons), parts of the brain, and methods of studying the brain.

Genetic Code

• Importance of Genetics in Behavior

  • Research indicates that not only physical traits but also behaviors can be inherited.

Chromosomes

• Definition

  • Structures within cells that carry genetic information.

• Human Chromosome Count

  • Humans possess 46 chromosomes total (23 pairs).

  • 22 pairs are autosomes (same in both males and females).

  • 1 pair is sex chromosomes (XX for females, XY for males).

• Genetic Material Inheritance

  • Each parent contributes half of the genetic material (23 chromosomes each).

  • X and Y Chromosomes

  • XX → genetically female.

  • XY → genetically male.

DNA and Nucleotide Base Pairs

• Structure of DNA

  • DNA (deoxyribonucleic acid) has a double helix structure.

• Nucleotide Bases

  • Four types: Adenine (A), Thymine (T), Guanine (G), Cytosine (C).

  • Denoted in genetic notation as ACTG.

• Function

  • Sequences of these nucleotides serve as a blueprint for the body’s structure.

Genes and Genotype vs. Phenotype

• Genes

  • Units of heredity that define traits.

• Genotype Definition

  • The genetic makeup of an individual; the sequence of nucleotides.

• Phenotype Definition

  • The observable traits expressed by an individual.

• Interaction between Genotype and Phenotype

  • Traits may not be expressed as intended due to environmental influences.

  • Example: Height influenced by health and nutrition despite genetic potential.

Inheritance Patterns

Alleles, Homozygous, and Heterozygous

• Alleles Definition

  • Different versions of a gene.

• Homozygous Definition

  • Same versions of a gene from both parents.

• Heterozygous Definition

  • Different versions of a gene from each parent.

Simplified Example: Eye Color

• Hypothetical Traits

  • Father: Brown eyes (dominant trait).

  • Mother: Blue eyes (recessive trait).

  • Result: Heterozygous offspring (brown and blue alleles).

Dominance and Recessiveness

• Dominant Gene Definition

  • Trait expressed regardless of the accompanying allele.

• Recessive Gene Definition

  • Trait expressed only when two recessive alleles are present.

Trait Example: Bitter Taste (PTC)

• Trait Overview

  • Tasting PTC largely determined by one gene.

• Alleles Explanation

  • Dominant version (T): ability to taste.

  • Recessive version (t): inability to taste.

• Parent Combinations

  • Assume both parents are heterozygous (Tt).

  • Possible Genotypic Combinations:

    1. TT → Homozygous dominant → Taster.

    2. Tt → Heterozygous → Taster.

    3. tT → Heterozygous → Taster.

    4. tt → Homozygous recessive → Non-taster (cannot taste).

• Phenotypic Ratios

  • From infinitely many offspring:

  • 25% Non-tasters (tt).

  • 75% Tasters (TT or Tt).

Complexity of Traits

• Polygenic Traits Definition

  • Traits controlled by multiple genes, common in psychology.

• Complexity in Genetics

  • Many traits are influenced by several genes and environmental factors.

  • Traits can exhibit hybrid characteristics beyond simple binary phenotypes.

Conclusion

• Summary

  • Understanding genetics helps in grasping behaviors and psychological traits.

• Note: Simplified genetic examples do not account for the complexity of most traits.