Multifactorial Inheritance DLA

Question 1

What are characteristics of multifactorial inheritance?

Answer 1

Proposed to account for common congenital malformations and acquired disorders that do not display a clear Mendelian pattern of inheritance but do show familial aggregation

Such disorders are thought to result from multiple genes of low impact/effect, and/or the interaction of genetic and environment factors

• do not produce discrete phenotype/genotype associations
• due to more than one gene affecting the trait
• alleles in this situation can be additive or non-additive
  - The number of contributing (dominant) alleles determines phenotype, not the specific combination(e.g. AbBb and AAbb have the same phenotype; mixed dominance= quantitative trait

Question 2

What is a polygenic trait?

Answer 2

Mutations or variants in more than one contribute to the trait

This occurs in complex inheritance as well and thus will be impacted by environmental traits

Question 3

What is the polygenic theory of quantitative traits?

Answer 3

Multiple genes affecting height, results in continuous variation (rather than discrete produced by single gene traits)

Th8s produces a normal/ Gaussian distribution

If height was only controlled by one gene e.g., two alleles. Gf1 and gf1= growth factor produced or growth factor not produced

Then the possible genotypes from two heterozygotes parents would be:

GF1/GF1= two doses of tallness
GF1gf1= one dose
gf1/gf1= no doses

Question 4

If height was controlled by two genes instead of one (no effect on environment)= digenic…

Answer 4

This would mean two genes= four alleles, resulting in five possible phenotypes from parents that are heterozugous at both loci

Question 5

What leads to the continuous phenotype?

Answer 5

The. Number of genes controlling the trait may determine the extent of the phenotypes observed

More genes= broader range of phenotype

Contributes to “continuous” phenotype-hence why we see this in polygenic traits

Question 6

What are some main polygenic traits?

Answer 6

• height
• weight
• skin color
• intelligence
• blood pressure

And of course are alll are influenced by the environment

These are quantitative trait loci- control of phenotypes that are measurable

Question 7

What role does environment play in height?

Answer 7

About 20% of height is controlled by genetics but the final ~80% is determined by environment (such as fetal and childhood nutrition)

So the bell shaped curve is broadened further to create continuous distribution