Introduction to Biopsychology: Human Genetics, Inheritance, and Gene-Environment Interactions

Evolution by Natural Selection and Genetic Fundamentals

Theory of Evolution by Natural Selection:
- Biology and biopsychology use the theory of evolution by natural selection to explain how human genes change over time.
- Natural selection states that organisms better suited to their environment will survive and reproduce.
- Traits that assist an organism in surviving and reproducing are encoded within its genes.
- Charles Darwin established the foundational principles of evolutionary theory.
Genes, Chromosomes, and DNA:
- Genes control or partially control physical characteristics in organisms.
- Genes are part of long strands of genetic information called chromosomes.
- Both genes and chromosomes are composed of DNA.
- DNA stands for deoxyribonucleic acid, which is a helix-shaped molecule that codes the information needed for an organism to take form and function.
Genetic Mutations and Alleles:
- Genes sometimes mutate, creating new physical traits.
- Physical Mutation Example: Genes can mutate to make red blood cells assume a crescent shape rather than a normal round shape, forming sickle-shaped blood cells.
- Different versions or mutated variations of the same gene are called alleles.
Survival Advantages and Natural Selection:
- If new genetic mutations provide an organism with a survival advantage, that organism will reproduce the mutated genes more effectively than organisms lacking those genes.
- Malaria Resistance Example: The crescent shape of sickle-shaped blood cells allows a child to resist malaria. Because of this survival advantage, more people with sickle-shaped blood cells survive, causing the mutated allele to be passed on and reproduced more effectively.

Genotype, Phenotype, and Genetic Inheritance

Definitions of Genotype and Phenotype:
- Genotype: The complete underlying genetic makeup of an individual.
- Phenotype: The actual physical expression of the genotype in the world.
- The phenotype is directly determined by the combination of alleles present in a gene.
Inheritance Patterns:
- For each gene, an individual inherits exactly one allele from each parent.
- Dominant Alleles: An allele is dominant if its presence guarantees its expression in the phenotype. For example, brown eye color is driven by a dominant allele ( $B$ ).
- Recessive Alleles: An allele is recessive if it is expressed only when both inherited alleles are identical. For example, blue eye color is driven by a recessive allele ( $b$ ).
- Expression of combined alleles determines phenotype: an individual with a genotype containing both a brown eye allele ( $B$ ) and a blue eye allele ( $b$ ) will have brown eyes because the brown eye allele is dominant.
Punnett Square Allele Interactions:
- A Punnett square demonstrates how dominant ( $B$ ) and recessive ( $b$ ) alleles for eye color interact across parental combinations:
- Genotype $BB$ : Inheriting two dominant alleles produces a dominant brown eye phenotype.
- Genotype $Bb$ : Inheriting one dominant allele ( $B$ ) and one recessive allele ( $b$ ) produces a dominant brown eye phenotype.
- Genotype $bb$ : Inheriting two recessive alleles ( $b$ ) produces a recessive blue eye phenotype.

Interaction Between Genes and the Environment

Environmental Influences on Gene Expression:
- The physical and behavioral expression of genes is directly influenced by environmental factors.
Range of Reaction:
- Range of reaction suggests that genes establish the boundary limits of behavior and potential, while the environment determines the exact behavior or level of achievement within those boundaries.
- Athletic Development Example: A child possessing great athletic skills is significantly more likely to reach the performance level of a professional athlete if raised in an environment that provides the opportunity, resources, and encouragement to express those genetic skills.
Genetic Environment Correlation:
- Genetic environment correlation suggests that specific genes may not be expressed at all if the surrounding environment is not suited to trigger or support them.
- Cancer Predisposition Example: A genetic predisposition to cancer may not actually lead to the development of cancer if the individual resides in an environmentally friendly environment.

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