Sickle Cell Anemia

Incomplete Dominance

Sex linked traits

Multiple Alleles
All chicken have combs on their heads, but it does not always look the same. The comb is a fleshy growth on the top of the chicken's head. Both male and female chickens have combs, but the ones on the male are larger. Combs of different breeds may look different in shape and even in color.
Chicken comb features: rrpp = single rrP_ = pea
R_pp = rose
R_P_ = walnut
1. What must be the genotypes of the two parents for the outcome to always be a walnut offspring?
(neither can be walnut to begin with) ____________ x _____________ = walnut (R_P_)
2. Show a Punnett square for the following cross and describe the phenotypic ratios. RrPp x RrPp
3. Show a punnett square for the following cross and describe the phenotypic ratios. rrpp x RrPp
4. Show a punnett square for the following cross and describe the phenotypic ratios. rrpp x rrPp
5. A rose crossed with a pea produces six walnut and five rose offspring. What must be the genotypes of the parents?
Show the cross.

• Natural selection acts on individuals, but only populations evolve
• Explain this statement

• Describes a non-evolving population
• The gene pool does not change
– Gene pool -
– Allele frequencies remain constant in nonevolving populations
• Why do this?
Allelic variation within a population can be modeled by the Hardy-
Weinberg equations.

http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/life4e_15-6-OSU.swf
The seven assumptions underlying Hardy–Weinberg equilibrium are as follows:
1. organisms are diploid
2. only sexual reproduction occurs
3. generations are non overlapping
4. mating is random
5. population size is infinitely large
6. allele frequencies are equal in the sexes
7. there is no migration, mutation or selection
Fig. 23-6

A population with 80% dominant and 20% recessive alleles that meets the conditions for Hardy-Weinberg equilibrium will pass 80% dominant and 20% recessive alleles to the next generation
Frequencies of alleles p = frequency of
C R allele = 0.8
q = frequency of
C W allele = 0.2
Alleles in the population
Gametes produced
Each egg: Each sperm:
80% chance
20% chance
80% chance
20% chance

Hardy-Weinberg equations:
p + q = 1
p 2 + 2 pq + q 2 = 1
Describes alleles in a gene pool
This is the equation for a trait with 2 alleles
Can be used to predict genotypes
p – represents dominant allele
q – represents the recessive allele
• Worksheet 3, 4 and 5

80% C R
( p = 0.8)
Sperm
C R
(80%)
20% C W ( q = 0.2)
Worksheet: #6
C W
(20%)
64% ( p 2
)
C R C R
16% ( qp )
C R C W
16% ( pq )
C R C W
4% ( q 2
)
C W C W

64% C R C R
, 32% C R C W
, and 4% C W C W
Gametes of this generation:
64% C R + 16% C R = 80% C R = 0.8 = p
4% C W + 16% C W = 20% C W = 0.2 = q
Genotypes in the next generation:
64% C R C R
, 32% C R C W
, and 4% C W C W plants

You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following:
The winged trait is dominant.
A. What is the frequency of the
"aa" genotype in the population?
B. What is the allele frequency of the "a" allele?
C. What is the frequency of the
"A" allele in the population?
D. What is the frequencies of the genotype "Aa” in the population?
E. What is the frequencies of the two possible phenotypes if "A" is completely dominant over "a."