Mendelian extensions

Question 1

Incomplete dominance

Answer 1

Heterozygous has intermediate phenotype

Question 2

Codominance

Answer 2

Heterozygous has both phenotypes

Question 3

Incomplete penetrance

Answer 3

Same genotype but not all affected

Question 4

Variable expressivity

Answer 4

Same genotype but different grades of affected

Question 5

Genetic/locus heterogeneity

Answer 5

Same phenotype but not same genotype

Question 6

Non-independent segregation

Answer 6

Some genes on the same chromosome might be linked. Measured in centiMorgan: 1cM = 1% recombinant progeny

Question 7

Multifactoral traits

Answer 7

Polygenic traits + environmental

Question 8

Quantitative traits

Answer 8

• Polygenic theory (Fisher, 1918): every quantitative trait is due to Mendelian traits with additive effects + environmental
• Liability theory: the probability of getting a disease is Gaussian, and if an individual in a specific population surpasses the fixed threshold they are sick. If they have other risk factors (sibs with sick people), their bell should be traslated.