Transcript C-13 Part II Non-Mendelian inheritance

C-13 Part II
Non-Mendelian inheritance
Most phenotypes reflect the
influences of several to many genes
and by the environment
Continuous variation
• When multiple genes act
together to produce a
physical (phenotypic)
character, a gradation or
range of differences
occur.
• Examples: height,
weight in humans
• Referred to as polygenic
traits
Pleiotropic effects
• Occurs when an allele
has >1 effect on
phenotype
• Examples are:
– Sickle cell anemia
– Cystic fibrosis
Incomplete dominance
• Situation where 2 alleles
“blend” to form
hybridized phenotype
• Examples:
– Flower color in 4
o’clocks and snapdragons
Environmental effects
• Allele expression may be
affected by environmental
conditions
• Examples:
– Coat color in arctic foxes
– Coat color in Himalayan
rabbits and Siamese cats
• ch allele affected by temp
>33 C  tyrosinase enzyme
inactivates + reduces
melanin pigment production
Epistasis – genes acting “in
concert”
• Situation whereby 1
gene pair affects the
expression of a 2nd gene
pair
• Examples:
– Anthocyanin (purple)
pigment in corn
– Animal coat colors
Epistasis (cont’d)
• Horse coloration involves
2 or more gene pairings..
• EE or Ee is for black
• ee is for red (sorrel)
• PLUS other genes can add
to base colors
• (Bay is AA, EE – black
with agouti gene;
Buckskin is AA, EE, CcrC
– bay with cremello gene,
Dun is AA, EE, Dd – bay
with dun gene; Palomino
is ee, CcrC – sorrel with
cremello gene)
Mutation of genes causes genetic
disorders
• Most gene disorders are RARE – nonadaptive
• Most are recessively inherited:
– Tay Sachs disease
Sickle cell anemia
• Some disorders are inherited in a dominant
fashion:
– Huntington’s disease
Multiple alleles and Blood Groups
• ABO Blood groups
–
–
–
–
IAIA and Iai = type A
IBIB and IBi = Type B
IAIB and IBIA = Type AB
ii = Type O
• Rh blood factor
• Rh +
• Rh-