Polygenic and Multi-factoral Inheritence

Question 1

What is incomplete dominance?

Answer 1

-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)

Question 2

What occurs if a trait is due to dominant expression of an allele? recessive expression?

Answer 2

• individuals can be AA or Aa and will present identically

- trait only present when both allele for that gene are the recessive version

Question 3

Co dominant genes?

Answer 3

-both phenotypes appear ex: sickle cell anemia

Question 4

How is sickle cell anemia an example of codominance?

Answer 4

-if have one sickle cell allele and one healthy allele, will have a mix of healthy & diseased blood cells

Question 5

How is sickle cell, recessive dominant & co-dominant?

Answer 5

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

Question 6

Multiple alleles ?

Answer 6

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

Question 7

Blood types alleles?

Answer 7

-there are 3 different alleles for blood type but 4 different blood types a person could have (AB, B , A or 0)

Question 8

How have 3 different alleles for blood type but 4 distinct blood types you can have?

Answer 8

• 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

Question 9

Polygenetic inheritance?

Answer 9

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

Question 10

Eye color?

Answer 10

• controlled by 3 genes
• 2 on chrom. 15 (linked); one on chrom. 19
• 6 alleles combined to give spectrum of color option

-called EPISTATIS

Question 11

what is epistasis?

Answer 11

• same idea as polygenetic inheritence

- occurs when two or more diff gene loci contribute to the same phenotype

Question 12

Which eye color is most dominant?

Answer 12

-dark colored eyes are dominant; so if inherit 6 dominant alleles will have very dark eyes

Question 13

incomplete dominance vs. polygenetic inheritance?

Answer 13

• polygenetic is about multiple GENES contributing to a phenotype,
• incomplete dominance is about 2 alleles on ONE gene

Question 14

What else effects if certain traits are fully expressed (based on genotypic outline)?

Answer 14

• diet, environment, etc

Question 15

What are continuous vs discontinuous (discrete) traits?

Answer 15

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

Question 16

Difficulty w/ determing number of genes that influence a trait?

Answer 16

• 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

Question 17

How is height determined?

Answer 17

• 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)

Question 18

What is multifactorial inheritance?

Answer 18

• when traits (diseases) are determined by genetic & environmental factors
• determined by V(total)

Question 19

How determine how much genetic vs. environment contribute to a trait?

Answer 19

• by analyzing similarities between relatives

- monozygotic twin studies since twins have same genotype so any differences have to result from env/ epigenetic

Question 20

Equation for determining Variance for common physical traits?

Answer 20

V(total)= V(genetic) + V(env) + V(interaction)

Question 21

What is relative risk? When is it highest?

Answer 21

• 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

Question 22

What is concordance? Why does it occur?

Answer 22

• 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

Question 23

Monozygotic twins and concordance?

Answer 23

• have identical genotypes

- degree of concordance of identical twins for a disease depends on how heavily genetics vs. env influence the trait

Question 24

What is a proband?

Answer 24

• the first individual that has been identified with the disease in a family
• in a pedigree, first shaded shape

Question 25

MS env vs genetic causes?

Answer 25

• 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

Question 26

Monozygotic twin prevalence for MS= 30%…what are the environmental influences?

Answer 26

~70% environment

Question 27

confound of determining relative risk for families?

Answer 27

• 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

Question 28

What does it mean by a multifactorial disease?

Answer 28

-that the disease is influenced by both genetic & environmental factors

Question 29

HapMap Project?

Answer 29

• identified and mapped 600,000 SNPs about 5000bp apart.

- aim was to use these to find genes that predispose people to common disease

Question 30

What is the genome-wide association study (GWAS)? Positives & negatives?

Answer 30

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)

Question 31

Examples of what GWAS has been used for?

Answer 31

-to identify risk genes for a number of common disorders like MS, Type 2 Diabetes, obesity, breast cancer etc.