Biological psych 4: Behavioural genetics (Lec 28) Flashcards
What is a phenotype, and what is the acronym for phenotypic variance?
The physical, measurable expression of a trait, resulting from the interaction of its genotype with the environment.
Vp is the acronym for phenotypic variance
Define the acronym Vg
Vg = Genetic variance
• = additive components (Va) + dominance components
(Vd) + gene interaction effects (epistasis) (Vi)
What is the formula for phenotype variance?
(Vp) = Vg + Ve + Vge
Define the acronym Vg
Vg = Genetic variance
What are the 3 main sources of phenotypic variance (Vp)?
– Vg = Genetic variance that a person is born with =
+additive components (Va)~sum of genes present
+ dominance components (Vd)~diff alleles of same gene, one may dominate and suppress another
+ gene interaction effects (epistasis) (Vi)~some genes modulate activity of other genes: Promotion or inhibition
– Ve = Environmental variance
• Common environment (Vc)
+ unique environment (Ve)
– Vge = Gene-Environment interactions
What are the 3 main sources of phenotypic variance (Vp)?
– Vg = Genetic variance that a person is born with =
+additive components (Va)~sum of genes present
+ dominance components (Vd)~diff alleles of same gene, one may dominate and suppress another
+ gene interaction effects (epistasis) (Vi)~some genes modulate activity of other genes: Promotion or inhibition
– Ve = Environmental variance
+Common environment (Vc)~shared b/ween ppl
+ unique environment (Ve)~unique to each person
– Vge = Gene-Environment interactions
Define homozygous and heterozygous genes
Homozygous gene: Same version of
Genes can vary between and within ppl. Give an example of how this takes place
Some gene loci may be dominant over others. Different versions of the same gene may be present in 2 locations.
Define homozygous and heterozygous genes
Homozygous genotype: 2 of the same version of the gene is present on the chromosome
Heterozygous gene: Different versions of same gene is present on the chromosome. In this case the recessive allele (version of gene) could be hidden by the dominant allele
Genes can vary between and within ppl. Give an example of how this takes place (genetic variance)
Some gene loci may be dominant over others. Different versions of the same gene may be present in 2 locations.
Explain the heretability formula h2 = V(g) / V(p)
Heritability is the component of the variance of the phenotype {V(p)} that can be explained by genetic variance (heritable factors) {V(g)}
What is the difference between monozygotic and dizygotic twins?
Monozyogtic twins are identical: same sperm and same egg, with a shared placenta
Dizygotic twins are fraternal: 2 sperm fertilised 2 eggs at the same time, with separate placenta
How do researchers estimate heritability using twins and siblings?
Measure some phenotypic trait and compare between monozygotic twins, dizygotic twins, Monozygotic twins raised apart and adopted siblings (adopted into family, compare against ‘biological’ children
Differences in these correlations can be
used to estimate V(g) (genetic variance) & V(e) (environmental variance)
What is meant by P = A + C + E = 1?
Give an example of how this applies to both monozygotic and dizygotic twins who were raised together
Phenotype= A (variance from additive genetic components) + C (variance from a common family environment) + E (variance from a unique personal environment)
r= correlation t= together (reared together)
eg rMZt = A + C = 1 - E
rDZt = 0.5A + C (o.5 represents 50% shared genetics)
How do the variant correlations personality and religiosity differ for MZ twins raised apart/ together? Are these effects replicated across diff lab studies?
Very little! Both around .5
No, the results are not reliable
What are the 2 important genetic factors which are not being taken into account for the lab studies on twins?
Name a twin studies case that did not suffer these limitations
- Twins as representative of the population? Not treated as average population
- Mis-estimation of variance in V(g) & V(e)- eg environments in same culture are still v similar, so twins raised in ‘different’ environments— V(g) is overestimated
Jack Yufe and Oskar Stohr, Jewish brought up in Jamaica and German in Hitler war time…still shared common traits although very opposed in views
What is candidate/ single gene analysis?
Give 2 examples
Studying the contribution of likely
candidates for a phenotype based on what
is known about their neurobiological bases
– Alcohol dehydrogenase for alcoholism
– Catecholamine-O-Methyltransferase (COMT) for cognition: No need to memorise this! It breaks down neurotransmitters such as dopamine
How might one study the contribution of single-gene variance twds certain psychological factors, using humans?
eg compare siblings w and w/out schizophrenia, take blood test to check for presence of genome, then test on cognitive task to compare performance w w/out that genome present
How might one study the contribution of single-gene variance twds certain psychological factors, using mice?
Manipulate genome in mice eg delete leptin gene in one sample (‘knockout gene’): this mouse can’t stop eating so we know leptin is important for apertite moderation
what are some problems w single gene analysis?
Ignores the important contribution of background
genotype to phenotype
– Effects of genetic manipulation might vary from strain to strain
– Some genes work because they regulate other genes. If you have a gene for something, it might depend on other genes being present to be active (epistasis)
What is pleitropy?
Pleiotropy = a single gene might contribute to more than one trait
What is redundancy i biology?
Redundancy = more than one gene produces the same effect, so knocking out a gene might have no visible effect on a trait
