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Warm up (in ISN):
• One cat carries heterozygous, long-haired
traits (Ss), and its mate carries homozygous
short-haired traits (ss). Use a Punnett square
to determine the probability of one of their
offspring having long hair.
Practice 2:
• In pea plants, spherical seeds (S) are dominant
to dented seeds (s). In a genetic cross of two
plants that are heterozygous for the seed
shape trait, what fraction of the offspring
should have spherical seeds?
Practice 3
• A white flowered plant is crossed with a plant
that is heterozygous for the trait. What
percentage of the offspring will have purple
flowers?
Practice:
• A purebred red cow (R) is crossed with a
purebred white cow (r). Draw a Punnett
Square depicting this cross, and write down
the genotypic and phenotypic ratios resulting
form this cross.
This is actually the phenotype for
heterozygous roan cows!
Alternative Patterns of Inheritance
• Not every trait works out perfectly-that is, one
trait is dominant, one recessive
• Exceptions to Mendel’s principles (one
dominant, one recessive)
Co-dominance
• Pattern of inheritance where both alleles are
dominant and therefore both phenotypes are
expressed
– Usually shown by two capital letters
– Example: roan cows, chicken feathers
Co dominance Practice:
• In a certain fish, blue scales and red scales are
codominant. When a fish has the genotype
BR, it has a patchwork of blue and red scales.
What happens if you breed this fish with a fish
that only has Blue Scales.
Incomplete Dominance
• Incomplete dominance-one allele is dominant
to another only to a certain extent, so it can’t
completely express its phenotype
– This results in phenotypes that are intermediate
– Example: snap dragons:
Incomplete/co Dominance Practice:
• Cross one white and one pink snapdragon.
Give phenotypic and genotypic ratios.
(incomplete dominance)
• Cross one white chicken and one chicken who
has black/white feathers. Give phenotypic
and genotypic ratios (co-dominant)
• Cross two red/white cows
Multiple alleles
• When there are more than two forms of one
gene
• Ex: Blood type, A B and O forms
Note-this is also an example of what type of inheritance?
Multiple Alleles practice:
• Mom has type O blood. Dad has type AB
blood. What percentage of their kids will
inherit type B blood?
Polygenic traits
• When a trait is controlled by one than one
gene
• For example eyecolor-look around
– Not just blue, green, brown, varying degrees
Eye color
Genes and the environment
• Environment can influence expression of
genes
– Genes contain information, environment can
determine how much of that information is
expressed
– Example: Western white butterflies, Siamese cats
Closure:
• Go back to warm up problem. Using what you
learned about co-dominance, fix your
genotypic and phenotypic ratios-hand into me
before you leave
Alien Genetics
• You are to create your own species of Alien. For
your alien, you must create 3 traits
– One trait must show normal dominant/recessive
relationships
– One must be co dominant
– One must be incompletely dominant
• Cross two purebred individuals showing the
different forms of these characteristics and the
resulting hybrid offspring
– Draw a Punnett square for each cross
– Draw each organism, showing the traits