Polygenic and Multi-factoral Inheritence Flashcards
What is incomplete dominance?
-when dominant & recessive traits are combined in the heterozygous state & result in a blending of the traits
-a mixture/spectrum of the phenotypes
-ex: mom= straight hair, dad=curly, kid= wavey
(yellow+ blue make green)
What occurs if a trait is due to dominant expression of an allele? recessive expression?
- individuals can be AA or Aa and will present identically
- trait only present when both allele for that gene are the recessive version
Co dominant genes?
-both phenotypes appear ex: sickle cell anemia
How is sickle cell anemia an example of codominance?
-if have one sickle cell allele and one healthy allele, will have a mix of healthy & diseased blood cells
How is sickle cell, recessive dominant & co-dominant?
Recessive: The anemia requires two diseased alleles
Dominant: malaria resistance only requires one healthy allele
Co-dominant: blood cell shape, will have both healthy and sickled cells if are heterozygous
Multiple alleles ?
When there are more than 2 alleles for a specific trait
-each individual can ONLY have two that determine their specific phenotype, BUT there can be many alleles to choose from
Blood types alleles?
-there are 3 different alleles for blood type but 4 different blood types a person could have (AB, B , A or 0)
How have 3 different alleles for blood type but 4 distinct blood types you can have?
- A & B alleles are dominant to O since O doesn’t encode a protein
- AA/BB or AO/BO
- O allele recessive (requires OO)
- A and B alleles are co-dominant, so AB genotype=AB blood
Polygenetic inheritance?
When a trait is controlled by more than one gene
ex: eye, skin, hair color, height etc
- means that have 3 genes (6 total alleles) that together control eye color
-gives continuous spectrum/ wide range of phenotypes in population
Eye color?
- controlled by 3 genes
- 2 on chrom. 15 (linked); one on chrom. 19
- 6 alleles combined to give spectrum of color option
-called EPISTATIS
what is epistasis?
- same idea as polygenetic inheritence
- occurs when two or more diff gene loci contribute to the same phenotype
Which eye color is most dominant?
-dark colored eyes are dominant; so if inherit 6 dominant alleles will have very dark eyes
incomplete dominance vs. polygenetic inheritance?
- polygenetic is about multiple GENES contributing to a phenotype,
- incomplete dominance is about 2 alleles on ONE gene
What else effects if certain traits are fully expressed (based on genotypic outline)?
- diet, environment, etc
What are continuous vs discontinuous (discrete) traits?
Continuous: vary along a continum, are associated w/ multiple loci/multiple alleles/env. influences
Discontinuous/Discrete: either/or not influenced by env, either have or do not, no spectrum
Difficulty w/ determing number of genes that influence a trait?
- the more genes that modify the trait, the harder it’s to tell how many genes there are
- cuz if have 1 gene= phenotypes….as we increase genes the alleles mix and change and can have a huge # of possible phenotypes
How is height determined?
- is a continuous trait and polygenetic
- is also heavily influenced by environment.
- famine during adolescence & childhood lead to decreased height
- due to positive correlation between nutrition and Insulin like growth factor (IGF-I)
What is multifactorial inheritance?
- when traits (diseases) are determined by genetic & environmental factors
- determined by V(total)
How determine how much genetic vs. environment contribute to a trait?
- by analyzing similarities between relatives
- monozygotic twin studies since twins have same genotype so any differences have to result from env/ epigenetic
Equation for determining Variance for common physical traits?
V(total)= V(genetic) + V(env) + V(interaction)
What is relative risk? When is it highest?
- relative risk compares risk of family members to risk in the general population
- relative risk for family members is highest for disease in which genotype plays a major role in causation, lowest for disease where genotype plays minor role
What is concordance? Why does it occur?
- the probability that a pair of individuals will both have a certain gene
- genetic diseases are more likely the more closely related a family member is to someone who has the disease
- because the more closely related 2 people are, the more alleles of a gene they share
Monozygotic twins and concordance?
- have identical genotypes
- degree of concordance of identical twins for a disease depends on how heavily genetics vs. env influence the trait
What is a proband?
- the first individual that has been identified with the disease in a family
- in a pedigree, first shaded shape
MS env vs genetic causes?
- epidemiology shows both env and genetic causes
- prevalence varies w/ geographic location, farther north= higher prevalence than life at equator
- if move before puberty you decrease env. effects, after puberty maintain risk level of original env
Monozygotic twin prevalence for MS= 30%…what are the environmental influences?
~70% environment
confound of determining relative risk for families?
- many families share all the same env. & risk factors
- means that studying them (since env is controlled) may look like heavy genetic linkage
- is why monozygotic twin studies who DON”T share same env are so important
What does it mean by a multifactorial disease?
-that the disease is influenced by both genetic & environmental factors
HapMap Project?
- identified and mapped 600,000 SNPs about 5000bp apart.
- aim was to use these to find genes that predispose people to common disease
What is the genome-wide association study (GWAS)? Positives & negatives?
1) looks at genome-wide set of genetic variants in different individuals to see if any variant is associated w/ a trait / disease
2) positive: allows us TO SEE WHICH GENES INFLUENCE DISEASE
3) negative: is need to compare a diseased group w/ healthy group so need >1000 people per group (A FUCK TON)
Examples of what GWAS has been used for?
-to identify risk genes for a number of common disorders like MS, Type 2 Diabetes, obesity, breast cancer etc.
