Download Genetics Objectives 22

Genetics Objectives 22
1.
Polygenic inheritance: a trait determined by an addition of a large number of
genes
Multifactorial inheritance: a trait determined by an addition of a large number
of genes as well as environmental factors
2.
1st degree relatives: parents and children (share ½ of the alleles)
2nd degree relatives: grandparents, grandchildren (share ¼ of the alleles)
3rd degree relatives: relatives for which a person shares 1/8 of their alleles
4th degree relatives: relatives for which a person shares 1/16 of their alleles
3.
Risk threshold in multifactorial models: risk threshold is the point at which
liability for a trait is exceeded and the abnormal trait is expressed phenotypically
4.
Principles of multifactorial inheritance:
a.
Familial aggregation: measured by the relative risk ratio (T, calculated
as: (prevalence of a disease in relatives of the individual)/(prevalence of a
disease in the general population)). When the risk ratio increases, the
genetic factor in the multifactorial trait increases.
b.
Twin studies: monozygotic twins share 100% of their genetic information,
and dizygotic twins share 50% of their genetic information. Thus, if
monozygotic twins share a trait less than 100% of the time, the trait must
be influenced by environmental factors. Similarly, if a trait is more
commonly shared between monozygotic twins than dizygotic twins, the
trait must be influenced by genetic factors. Multifactorial traits show less
than 100% concordance between monozygotic twins, but a higher
concordance in monozygotic twins than dizygotic twins.
5.
Multifactorial diseases more common in males:
a.
Pyloric stenosis
b.
Club foot
c.
Cleft lip and palate
Multifactorial diseases more common in females:
a.
Hip dislocation
b.
Scoliosis
c.
Isolated cleft palate
6.
Use principles of multifactorial inheritance to assess risk of patient:
a.
Risk increases with increasing degree of relatedness
b.
Risk increases with increasing number of affected relatives
c.
Risk increases with increasing severity of disease
d.
Risk increases in offspring of less liable sex parents for diseases that show
a greater liability in one sex (risk increases for pyloric stenosis if it is in
the maternal side of the family)