L18: Quantitative Genetics Flashcards
True or False:
Eye colour is monogentic
False
Eye colour is polygenic, controlled by more than 1 gene
What determines eye colour?
Number of melanosomes in the iris
What are melanosomes?
Melanin-containing structures
What are melanocytes?
Cells in the iris that produce & contain melanin
Melanosomes in terms of:
brown eyes
green eyes
blue eyes
Brown: Plenty
Green: Intermediate no.
Blue: Very little
Why do people have blue eyes?
Scattering of light by protein particles in the iris
What colour eyes do albinos have and why?
Red eyes
- No melanin made
- Red light replaced from blood cells
What are the determinants of differences in eye colour ?
1) No. of melanosomes
2) How much melanin they store
3) Which type of melanin they store
What 2 routes can melanin synthesis lead to?
1) Eumelanin (Brown-black)
2) Pheomelanin (Red-yellow)
What is OCA2?
Transporter protein found in membranes of melanosomes
What is approx 75% of eye colour variance due to?
Mutations in the OCA2 locus
What is quantitative inheritance?
Describe traits with continuous variation
What are quantitative traits influenced by many genes & environmental factors referred as to?
Multifactorial/complex traits
What is the ratio of 5 phenotypic classes with two loci (AaBb x AaBb)?
1:4:6:4:1
What is heritability?
Measures how much phenotypic variation is due to genetic differences
What does a value close to 1 & 0 indicate?
Close to 1: strong genetic control
Close to 0 : strong environmental control
What can be used to allow an estimation of heritability in humans?
Twin studies
Describe:
Monozygotic Twins
Dizygotic Twins
Monozygotic: Single zygote splitting to give rise to genetically identical embryos
Dizygotic: 2 different zygotes- 50% genetic identity
What does concordance measure?
How often BOTH twins express a trait
Concordant: if they both express it
Discordant: if 1 express it & another doesn’t
What does the threshold model explain?
How genetic & environmental factors combine to influence risk of developing disorder
2 ways to identify genes involved in a trait
1) GWAS (genome wide association studies)
2) SNPs (single base pair changes between genomes of individuals)
