Genetic and Environmental Influences

genotype

the genetic material we inherit from our parents

phenotype

the observable expression of the genotype, including bodily charcteristics and behavior

parent’s genotype—child’s genotype

the human being has 46 chromosomes (23 pairs) & half of each pair comes from each parent

child’s genotype—child’s phenotype

many genes are never or only partially expressed, 1/3 of genes have 2 or more different forms (alleles)

alleles

versions of the same gene on a pair of chromosomes, appear at same place on each chromosome in the pair, one allele is inherited from each parent

homozygous

two alleles are the same

heterozygous

the alleles are different

polygenic inheritance

complex behavioral traits involve contribution by multiple genes; the phenotype is often on a continuum, not present/absent

child’s environment—child’s phenotype

environment influences gene expressions

child’s genotype x child’s environment = child’s phenotype

canalization

• the suppression of phenotypic variation in a population

  • insensitive to genetic mutations

  • insensitive to environmental variation

  • stabilizing function on key developmental pathways

child’s phenotype — child’s environment

• a child’s temperament, IQ, and talents elicit certain responses from others (leads to evocative gene-environment)

• children seek out and prefer environments which are conducive to their interests, talents, and personality characteristics/niche-picking (leads to active gene-environment correlation)

evocative gene-environment correlation

a child’s genetic endowments elicits certain experiences or interactions with the world

active gene-environment correlation

children select environments best suited to their genetic predisposition

parent’s phenotype — child’s environment

• the environments that parents choose and provide for their children are partially shaped by the parents’ phenotype (interests, talents, affinities)

• leads to passive gene-environment correlation

passive gene-environment correlation

environment in which child is raised is shaped by parent’s genes, which are also part of child’s genetic endowment

heritability

measure of the extent to which individual differences on a given trait in a specific population are attributable to genetic differences among those individuals (0<H<1)

heritability caveats

• applies only to populations (not individuals)—you can’t say Johnny’s heritability of IQ is .5

• applies to only a particular group living in particular environment and particular time

• rarely exceeds 0.5, indicating the large contribution of environmental factors

epigenesis

• development results from ongoing, bidirectional exchanges between heredity and all levels of the environment

• both the internal environment (hormones, toxins, etc) and the external environment (family, neighborhood, etc) modify gene expression without modifying genotype