DNA
Deoxyribonucleic acid
Molecules that carries the biochemical instructions involved in the formation and functioning of organisms.
Gene
Section of chromosomes and portions of DNA
Basic unit of heredity
Chromosome
thread-like molecules made up of DNA, containing many genes
Genome
The complete sets of genes in any organism
Genotype
the genetic material an individual inherits
Phenotype
the observable expression of the genotype, including body characteristics and behaviour
Environment
includes every aspect of the individual, and his or her surroundings, other than genes
Karyotype
an individual’s complete set of chromosomes
What is Mutation?
A change in a section of DNA. Caused by random or environmental factors (e.g., teratogens)
Random assortment
The shuffling of the 23 pairs of chromosomes - chance determines which member of the pair goes into the new sperm and egg
-> makes 2^23 different combinations
Crossing over
The process by which sections of DNA switch from one chromosome to another during meiosis, further increasing genetic variability
Regulator genes
control the switching on and off of genes that underlie development across the lifespan
Why are regulator genes needed?
- A given gene influences development and behavior only when it is turned on
- Important for healthy development
Alleles
- Different forms of the same gene
- Therefore give rise to different phenotype
- 2 sub-types: dominant (expressed if present), recessive (not expressed if dominant allele is present)
Heterozygous
A person who inherits two different alleles for a
trait
Homozygous
A person who inherits two of the same allele for a
trait
Mendelian inheritance patterns
Basically for heterozygous parents (coded as Bb), offsprings can be:
1 BB - homozygous dominant
2 Bb - heterozygous
1 bb - homozygous recessive
-> limitation of mendelian inheritance pattern: only account for single gene features (hair colour, eye colour)
What is meant by the “male disadvantage”?
Individuals with only one x-chromosome (e.g. male XY) are more likely to suffer a variety of inherited disorders caused by recessive alleles on the X chromosome (e.g., color blindness)
Reason:
- Y chromosome has only about a third of X chromosome’s genes
- Many alleles on the X chromosome do not have a corresponding allele on the Y chromosome that could suppress the action.
Types of genetics-origin diseases and disorders in humans + examples?
over 5000 are known to have genetics-origin
- recessive gene: sickle-cell anaemia, PKU, cystic fibrosis
- single dominant gene: Huntington’s disease
- sex-linked: hemophilia, Fragile-X syndrome
- error in meiosis (zygote with different number of chromosome components): Down syndrome - trisomy 21
Polygenetic inheritance
- Inherited characteristics are governed by more than one gene (e.g. height, intelligence)
- Polygenetic inheritance applies to most traits and behaviors of interest to behavioral scientists
Norm of Reaction (Dobzhansky, 1955)
all possible phenotypic outcomes, that could theoretically result from a given genotype in relation to its environment.
Example of Norm of reaction (PKU)
- Children with phenylketonuria (PKU)— a disorder that is related to a defective gene on chromosome 12—are unable to metabolize phenylalanine (e.g. food sweetener)
- With early diagnosis and a properly restricted diet -> cognitive impairment can be avoided
Example of Norm of reaction (MAOA)
- Men who have experience severe malnutrition (environment) are more likely to engage in antisocial behavior
- INCREASE effect with inactive MAOA gene
What is study in Behaviour Genetics?
- How variation in behaviour and development results from the combination of genetic and environmental factors (mainly in family-study)
- Correlations between the measure of the trait in individuals with different relationships are examined to see whether larger effect for environmental-basis (share environment) or genetic-basis (twins)
