Transcript Punnet Squares

Punnet Squares
• YY x yy (These are in the P1 generation)
y
y
Y
Y
Yy
Yy
Yy
Yy
(These are in the F1 generation)
•What are the chances
that the offspring will
have a heterozygous
genotype?
•What are the chances
that the offspring will
have a dominant
phenotype?
What if F1 is self-pollinated?
• Yy x Yy (F1 generation)
Y
y
Y
y
YY
Yy
Yy
yy
(These are in the F2 generation)
•What are the chances
that the offspring will
have a heterozygous
genotype?
• …hom. dominant?
• …hom. recessive?
•What are the chances
that the offspring will
have a dominant
phenotype?
Summary of Mendelian genetics
• Only two possible phenotypes
• Dominant completely masks the recessive
• F1 generation is 100% heterozygous genotype;
100% dominant phenotype
• F2 generation demonstrates the following ratios:
genotypic ratio-- 1 : 2 : 1
phenotypic ratio-- 3 : 1
Incomplete Dominance
• One allele is not completely dominant over
the other
• Heterozygous is some where in-between in
color
• Example: Four o’clock plants
RR= Red flowers
RW= Pink flowers
WW= White flowers
Problem
A red flowered four clock
plant is crossed with a
pink four clock plant.
What are the possible
genotypic and phenotypic
ratios of the offspring?
Codominance
• Both alleles contribute to the phenotype
• Heterozygous appear to be a blend of the
colors
• Example: Chickens
BB= black feathers
WW= white feathers
BW= black and white feathers
Problem
A chicken breeder mated a
black chicken with a white
chicken and all his chicken
were checkered in color.
He decided to mate two of
these chickens. What are
his expected genotypic and
phenotypic outcomes?
Multiple Alleles
• When more than two alleles are possible for a
gene
• Individual only gets two out of all the
possibilities
• Example: Human blood types IA or IB or i
IAIA or IAi = A
IBIB or IBi = B
IAIB = AB
ii = O
Polygenic Traits
• Traits produced by the interaction of many
genes
• Skin color, height, eye color and others
Sex Linked
 a trait that is controlled by genes found on a
sex chromosome (usually the X
chromosome)
 ex. Color blindness; male-pattern baldness