chapter 7 - complex traits Flashcards
mendelian traits
caused by a single gene
polygenic traits
caused by multiple genes
polygenic trait examples
height, skin color, body weight, illnesses, etc
single gene traits often produce an _______ effect
all or none
polygenic traits produce a continuously _____ phenotype
varying
polygenic traits can also be called ______ traits
quantitative
Quantitative Trait Loci
QTL’s; name for DNA sequences
frequency of distribution of phenotypes forms a __________ curve
bell-shaped
empiric risk
used to predict the chance that a polygenic complex trait will occur in an individual based on familial relationship; uses the incidence of the characteristic in a specific population
incidence
rate at which a certain event occurs
prevalence
proportion/number of individuals who have a particular trait at a specific time
empiric risk is not a calculation, but a ….
population statistic based on observation
empiric risk increases with 3 things:
1) severity of disease
2) number of affected family members
3) how closely related a person is to affected persons
heritability
estimates the proportion of variation in a complex trait due to genetics in a particular population at a certain time; refers to the degree of variation in a trait due to genetics, and not to the proportion of the trait itself attributed to genes
heritability equals ____ for a trait whose variability is completely the result of gene action
1.0
broad-sense heritability
H^2
sibling to sibling % shared genes (coefficient of relatedness)
50%
parent to child % shared genes (coefficient of relatedness)
50%
uncle/aunt to niece/nephew % shared genes (coefficient of relatedness)
25%
half-siblings % shared genes (coefficient of relatedness)
25%
grandparent to grandchild % shared genes (coefficient of relatedness)
25%
first cousin to first cousin % shared genes (coefficient of relatedness)
12.5%
concordance
measures the frequency of expression of a trait in both members of monozygotic or dizygotic twins
discordant
twins who differ in a trait
dizygotic twins
shared environment % 50% of genes
monozygotic twins
identical genotype and shared environmnet
genome-wide association study (GWAS)
compares many genetic markers across the genome between 2 large groups of people, usually 1 with a particular trait/disease and 1 without it
GWAS uses genetic markers, including SNP’s and CNV’s
single nucleotide polymorphisms, copy number variants
single nucleotide polymorphism (SNP)
a site in the genome that has a different DNA base in >1% of a population
copy number variation (CNV)
tandomly repeated DNA sequence
to achieve statistical significance, a GWAS must include at least _____ markers
100,000
study designs in GWAS
- cohort study
- case-control study
- affected sibling pair strategy
- homozygosity mapping
cohort study
researchers follow a large group of individuals over time and measure many aspects of their health
case-control study
pairs of individuals are matched so that they share as many characteristics as possible
affected sibling pair strategy
tests identify SNP’s that siblings with the same condition share but that siblings who do not both have the condition do not share
homozygosity mapping
disease-causing mutations are identified in homozygous genome regions that children inherit from parents who are related to each other
limitations of GWAS
- so much data - prone to error
- reveal associations between information, not causes
- bias can be a part of it
- accuracy is affected by complicating factors like phenocopy and epistasis
- could miss rare SNP’s
body mass index BMI
weight (kg) / height2^2(m^2)
leptin
protein hormone produced by fat cells
- signals the hypothalamus to decrease appetite
- acts in the long term to maintain weight
ghrelin
peptide hormone produced in the stomach
- responds to hunger by increasing appetite
- functions in the short term to regulate weight
