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3.1 Human Genetics

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  • Psychologists study genetics to further understand biological factors that contribute to certain behaviors.

  • Theory of Evolution by Natural Selection

    • organisms better suited for their environment will survive and reproduce while those that are poorly suited for their environment will die off
    • proposed by Charles Darwin

  • Not only traits but also patterns of cognition and behavior are also coded inside the genes.

  • Evolutionary psychologists study universal patterns of behavior and cognition that may have evolved as adaptations (fear response, food preference, mate selection, etc.)

  • Behavioral geneticists study how individual differences arise through interaction of genes and the environment.

Genetic Variation

  • refers to the genetic difference between individuals

  • contributes to a species’ adaptation to its environment

  • in humans, it begins with an egg, about 100 million sperm, and fertilization.

  • Chromosomes

    • long strings of genetic material called deoxyribonucleic acid (DNA)
    • the egg and the sperm each contains 23 chromosomes.

  • Deoxyribonucleic Acid (DNA)

    • a helical-structured molecule made up of nucleotide base pairs
    • sequences of DNA form genes that, either fully or partially, control a number of visible characteristics (eg. hair color, eye color, etc.)

  • Allele

    • a specific “version” of a gene
    • a single gene may have different possible variations or alleles (eg. the genes for hair color may have a version for brown hair or black hair. each version is called a different allele)
    • one way to understand this is that a given gene may control eye color, and different alleles of that gene affects which eye color an individual has.

  • During fertilization, when a sperm and egg fuse, their 23 chromosomes combine to create a zygote with 46 chromosomes

    • This means that each parent contributes to half of the genetic information carried by their offspring.

  • Genotype

    • the genetic makeup of an individual.

  • Phenotype

    • refers to the individual’s inherited physical characteristics.

  • In genetics, the genetic parent is described as the individual organisms that contribute genetic material to offspring.

How Genetic Traits are Passed

  • A trait controlled by a single gene (monogenic) is influenced by a single gene from each parent.

  • Having a dominant allele either from one parent (Bb) or two parents (BB) will always result in the same dominant trait phenotype

    • When someone has two copies of the same allele, we call it homozygous
    • When someone has a combination of alleles in a given gene, we call it heterozygousa

  • If they are homozygous for a recessive allele, it will only display the recessive trait phenotype

  • Example:

    • We will call the gene for black hair and brown hair .
    • The black hair trait is a dominant allele
      • This means that if one of your parents , or both of them has the dominant allele, then their offspring will result in a black hair.
    • The brown hair trait is a recessive allele
      • This means that if only both parents are homozygous for that recessive allele , then their offspring will result in brown hair.

  • Some genes are polygenic, controlled by two or more genes.

  • Examples of polygenic traits are height, weight, and skin color.

Mutations

  • a sudden, permanent change in a gene

  • some mutations can be harmful and lethal while some may benefit an individual with an advantage

  • Due to theory of evolution, individuals best adapted to their particular environments are more likely to pass their genes to the future generations

    • In order for this to occur, there must be variability in genes.
    • If everyone would be the same, then any dramatic changes in the environment would affect everyone in the same way.

Gene-Environment Interactions

  • Range of Reaction

    • the genes set the boundaries within which we can operate and the environment interacts with the genes where in that range we will fall
    • Example: if the genes of a child tell that they have high intellectual potential, then the environment dictates whether they can achieve its full genetic potential or not.

  • Genetic Environmental Correlation

    • the genes influence the environment and the environment influences the expression of genes
    • Example: if the child of an NBA player would probably be exposed to basketball at an early age, then the exposure might allow the child to achieve their full genetic, athletic potential.

  • Epigenetics

    • a subfield of genetics that focuses on how the same phenotype can lead to very different phenotypes
    • states that the genotype is not fixed and limited and that their phenotypes may differ based on how their genetic information is expressed over time and through their unique environmental interactions.

  • Genes also affect behavioral characteristics, from basic personality traits, sexual orientation, to spirituality

  • Genes are also associated with temperament and some psychological disorders.

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