Multifactorial Inheritance

Question 1

multifactorial inheritance definition

Answer 1

• combined contribution of genes and environmental factors in the causation of a particular disease or trait

Question 2

trait

Answer 2

distinct variant of a phenotypic characteristic that may be inherited

Question 3

single gene trait

Answer 3

results from the influence of only one gene

Question 4

multifactorial trait

Answer 4

results from the combined influence of multiple genes and environmental factors

Question 5

signs of multifactorial inheritance

Answer 5

• no clear mendelian inheritance
• absence of clear defects from a single abnormal gene
• VARIATION in severity and expression of phenotype
• gender differences in frequency of occurrence

Question 6

quantitative traits

Answer 6

• think number (continuous range of measurement)
• follows a normal distribution curve
• e.g. height, weight

Question 7

threshold traits

Answer 7

• think presence or absence of trait
• bell-shaped distribution of liability
• once ind. exceeds the threshold of liability

Question 8

liability

Answer 8

total combined genetic and environmental factors that influence the development of a multifactorial disorder or trait

• once past the threshold, you’re affected
• liability cannot be measured (determined from the incidence of the disease in a group)

Question 9

liability sex differences

• cleft lip and palate
• congenital hip dysplasia
• pyloric stenosis

Answer 9

• cleft lip/palate M > F
• congenital hip dysplasia
  F > M
• pyloric stenosis M > F
  digestive problems

Question 10

recurrence risk rules for multifactorial inheritance

Answer 10

• proband more severe, greater risk
• more than one fam member, greater risk
• distantly related, risk decreases
• proband is of less commonly affected sex, greater risk
• risk for 1st degree relatives is approx sq. rt. of population incidence of trait
• in GENERAL, recurrence risk is approx 4%, but if defect is part of underlying syndrome, could be much higher

Question 11

heritability

Answer 11

measure of proportion of total phenotypic variance of a trait that is caused by a gene
- always between 0 and 1

Question 12

twin studies

Answer 12

• heritability of a trait estimated for concordance rates for monozygotic twins and dizygotictwins
• if MZ share a trait more often than DZ, then more genetic

Question 13

Linkage analysis

Answer 13

• determine whether inheritance of a marker predisposes to a certain trati/disease in family
• identifies a region of genome where candidate disease allele could be found