Download 5InheritancePatterns14_15

Inheritance Patterns
Chapter 14.3 - 15
What you need to know!
• How to derive the proper gametes when
working a genetics problem
• How to read a pedigree
• The unique pattern of inheritance in sexlinked genes
Patterns of Inheritance
• Complete dominance: rule of dominance
where YY and Yy have the same
phenotype
• Codominance: two alleles are dominant
and both are equally visible (patches of
color in dogs)
• Incomplete dominance: two alleles are
dominant and both mix to form a new
phenotype
Patterns of Inheritance
• Multiple alleles: when a gene has more
than two alleles (blood type)
• Pleiotropy: one gene with multiple
phenotypic effects
• Epistasis: a gene at one locus alters the
effects of a gene at a different locus
• Polygenic Inheritance: two or more genes
impact a single phenotype
Patterns of Inheritance
• Sex-linked genes: alleles loci are on a sex
chromosome (X or Y in humans)
– Punnett Square must include the sex
chromosomes
• Sex-linked disorders are most common in
men (because they only have 1 X
chromosome)
– Duchenne muscular dystrophy, hemophilia,
red-green color blindness, baldness, etc.
Dominant Disorders
• Achondroplasia - dwarfism
• Lethal Dominant alleles: only possible for
late onset genes
– Huntington’s Disease: degenerative disease
of the nervous system; 40 years of age +
Lethal Recessive Alleles
• Requires two copies of the lethal recessive allele
• Cystic fibrosis: mutation in cell membrane protein;
mucus is thicker and stickier  organ malfunction
and increased infection rate
• Tay-Sachs: mutation in an enzyme; can’t break
down lipids in the brain  blindness, seizures,
degeneration, and death
• Sickle-Cell: mutation in hemoglobin; forms rods
when O2 levels are low  sickle shaped cells that
clog small blood vessels which cause pain, organ
damage, and paralysis
Genetic Testing
• Amniocentesis: draw fluid from the
amniotic sac (small risk)
• Chorionic villus sampling: suction out a
tiny sample of the placenta
Pedigrees
• Track inheritance patterns of traits and/or
disorders
• Circles are females, squares are males,
color coded key