Week 3 - Genetics and Intellectual Disability

genotype

particular set of genes that a person inherits from his or her parents

example: genotype= bb (recessive =b)

phenotype

the behavioral product of the interaction of a person’s genotype with the environment

example: genotype= bb (recessive =b) therefore phenotype is blue eyes

ovum

the female germ cell

sperm

the male germ cell

meiosis

cell division of germ cells

mitosis

cell division of body cells

chromosomes

threadlike structures located in the nucleus of the cell that carry genetic information

• 23 from each parent

how many sets of chromosomes are inside of a nucleus

46

DNA

stores all the coded information that influences what you look like, your body functions and psychological functions 

genes

sections of DNA which contain complete messages

inheritance

transmission of maternally and paternally derived genes

• characteristics may come from one chromosome or gene

polygenic inheritance

due to multiple genes that determine complex behaviors such as intelligence, sociability

sex linked inheritance 

genes that are carried on the X chromosome

fragile x

damage to the X chromosome causes intellectual disability and associated attention and social difficulties

mutations

not inherited, they are due to problems during meiosis (e.g., down syndrome)

what occurs when there are three instead of 2 chromosomes 21?

chromosomal atypicality due to failure to separate pair 21 and leads to extra genetic material

• causes intellectual disability, motor and language difficulties

genotype-environment correlation

parents give their biological offspring both their genes and a home environment, but both are a function of the parents’ own genes, providing a built-in correlation between the individual’s genotype and his or her early home environment

reactive interaction

different persons exposed to the same environment experience it, interpret it, and react to it differently

evocative interaction

each individual’s personality evokes distinctive response from others

example: siblings with different temperament

• inhibited vs exuberant

proactive interaction

different individuals select and construct different environments. as a child gets older and begins to select and construct environments of his or her own, the effect of the built-in genotype-environment correlation diminishes and the influence of proactive interaction increases. Reactive and evocative interactions remain important throughout life

identical twins shared genes and environments

share genetic material and home environment

fraternal

do not share genetic material - uterine environment and family environment

identical twins reared apart

share genes but not home environment 

reaction range: dynamic developmental construct

• human being’s genetic makeup establishes a range of possible developmental outcomes

• within these boundaries it is environmental factors that largely determine how the person develops over time

how can environment directly impact the function of genes?

environment/lifestyle may change the function of those genes. that is when and how they work

epigenetics

external modification to DNA that turn genes “on” or “off”

• modifications do not change the DNA sequence, instead, they affect how cells “read” genes

DNA methylation

addition of a methyl group, or a “chemical cap” to part of the DNA molecule, which prevents certain genes from being expressed

histone modification

Proteins that DNA wraps around. Without histones, DNA would be too long to fit inside cells. the DNA cannot be “read” by the cell. modifications that relax the histones can make the DNA accessible to proteins that “read” genes

top-down approach to studying genetic DD

observes behavioral characteristics to give clues to genes

• e.g., extreme behaviors such as overly social behavior in William’s syndrome

bottom-up approaches to studying genetic DD

begins with genes to cells and then behavior

• e.g., number of gene deletions is related to severity of William’s syndrome 

endophenotype approach to studying genetic DD

in between genes and behavior

• e.g., study performance on attention, social cognition, executive function tasks