Download The ability to taste the chemical PTC is determined by a single gene

The ability to taste the chemical PTC is
determined by a single gene in humans with the
ability to taste given by the dominant allele T
and inability to taste by the recessive allele
t. Suppose two heterozygous tasters (Tt) have a
large family.
a. Predict the proportion of their children who
will be tasters and non-tasters. Use a Punnett
square to illustrate how you make these
predictions.
Tall is dominant to short
If two tall individuals mate, and they
have a child who is short, what are the
genotypes of the parents?
Incomplete Dominance
• Explain what is meant by incomplete
dominance.
A cross between a blue blahblah bird & a white
blahblah bird produces offspring that are silver. The
color of blahblah birds is determined by just two
alleles.
a) What are the genotypes of the parent blahblah
birds in the original cross?
b) What is/are the genotype(s) of the silver offspring?
c) What would be the phenotypic ratios of offspring
produced by two silver blahblah birds?
In some cats the gene for tail length shows
incomplete dominance. Cats with long tails and cats
with no tails are homozygous for their respective
alleles. Cats with one long tail allele and one no tail
allele have short tails. For each of the following
construct a punnett square and give phenotypic and
genotype ratios of the offspring.
a) a long tail cat and a cat with no tail
b) a long tail cat and a short tail cat
c) a short tail cat and a cat with no tail
d) two short tail cats.
Codominance
• Explain what is meant by Codominance
A cross between a black cat & a tan cat produces a
tabby pattern (black & tan fur together).
a) What pattern of inheritance does this illustrate?
b) What percent of kittens would have tan fur if a
tabby cat is crossed with a black cat?
• In shorthorn cattle, when a red bull (RR) is
crossed with a white cow (WW), all of the
offspring are roan (a spotted, red and white
color). What offspring are expected from
mating a roan bull and a roan cow?
Dihybrid Practice
• Yellow fruit and dwarf vines are recessive traits in
tomatoes. Red fruit and tall vines are dominant.
Complete a dihybrid punnett square and answer the
questions for a completely dominant red and tall plant
crossed with a heterozygous red and dwarf plant (You
choose the letters you want to use).
• What percent of the offspring will be totally
heterozygous?
• What is the phenotypic ratio?
• What percent of the offspring will have yellow fruit and
dwarf vines?
Trihybrids
• DO NOT COMPLETE A 64 box punnett square!
That is too much work!
• Instead! USE PROBABILITY!!
Trihybrids Practice
• Suppose each letter represents a trait (Uppercase
being dominant and lowercase being recessive)
• The Two parents being crossed have the following
genotypes:
– AaBBCc x AABbcc
– What is the probability that their offspring will have
the genotype of AaBbCc?
– What is the probability that their offspring will have
the genotype of AABBcc?
Most Missed Quiz Questions
• 5 and 6
• Yellow is dominant to green. Snap Dragon
flowers are incomplete dominant
• 5) If two pea plants are crossed and one is a
true bred yellow and the other is green, how
many of the 16 offspring would be yellow?
• 6) If a pink snap dragon is self-pollinated and
produces 120 offspring, how many would you
expect to be red?
• A short haired black guinea pig (heterozygous
for both traits) is crossed with a long haired
white guinea pig. What is the expected
genotypic ratio of the offspring?
Dihybrid using a short cut
• Round is dominant to wrinkled and tall is
dominant to short
• Two round, tall pea plants (heterozygous for
both traits) are crossed. How many individuals
are expected to be short and round?
Trihybrid Practice
• AaBbCc x AaBbCc
• Probability of offspring with an aaBBCc
genotype?
• Cross a AabbCcDD x aaBBCCDd
• What is the probability of AaBbCcDd?
Review All Types SO FAR…
• What were the phenotypes of the parents if
25 red flowers, 50 pink flowers and 25 white
flowers were produced?
• A. pink and pink
• B. pink and red
• C. CRCR and CWCW
• D. CRCW and CRCW
• If a family has 2 girls, what is the probability
their next daughter will be a girl?
• A. ½
• B. 1/8
• C. 1/16
• D. 1/32
• E. Unpredictable
• In mice, black fur is dominant to brown fur
• A cross between two heterozygous mice,
produced 3 black mice, and one brown
mouse.
– What kind of inheritance does this represent?
• The same parent mice were bred, but this
time, produced a white mouse.
– How do you explain this?