Download Incomplete Dominance

Incomplete Dominance
•What do you notice about the
picture?
• Incomplete dominance is when the two alleles
inherited from the parents are neither
dominant nor recessive, but blend together
to give a physical trait that is somewhere
between the two.
• The most well-studied example of incomplete
dominance in humans occurs in the genes for
curly hair. Inheriting a gene for curly hair from
one parent and a gene for straight hair from
the other parent will give a hair texture that is
a blend of the two, wavy hair.
✔Check for Understanding
• In some flowers (snapdragons), an allele for
red flowers when combined with an allele for
white flowers will result in pink flowers. Show
a cross between a red flower and a white
flower.
• What percent of the F1 generation will be
Red
____________
Pink ____________
White ____________
Next cross two pink flowers, what percentage will be
red, pink and white?
Codominance
• “Co” in front of a word means “together”.
Codominance is similar to incomplete
dominance because neither allele is fully
dominant or recessive.
• However, where incomplete dominance is a
blending of the two alleles, with codominance
BOTH alleles are expressed with no blending.
• We usually show the alleles (genotype) of
codominance as:
• RR=Red
• RW=Striped
• WW=White
Both Alleles are Capitalized!
✔Check for Understanding
• RR=Red
• RW=Striped
• WW=White
• Suppose you own a nursery (green house) and you
know striped flowers sell the best and give you the
most profits, show the cross that would be necessary to
get the MOST striped flowers.
✔Check for Understanding
• Show what would happen if you crossed two
striped flowers below:
• What would be the phenotypic ratio of the
offspring?
The
• Roan color is the result of
crossing a red cow with a white
cow. The cross between these
two ends up giving the
offspring some hairs of each
color.
Give the genotypes and phenotypes
of the cow:
Genotype
Phenotype
RR
Rr
______
__________
Red and white
White
✔Check for Understanding
• Predict the phenotypic ratio of a cross
between a roan bull and a white cow.
Polygenic Traits
• Many traits are controlled by more than one
gene. These genes may be located on
different chromosomes.
• An example of a trait that is controlled by
many genes is eye color.
✔Check for Understanding
• What are some other polygenic traits in
humans that you can think of?
• 1. ___________________
• 2. ___________________
• 3. ___________________
Multiple Alleles
• A number of human traits are the result of
more than 2 types of alleles.
• With multiple alleles there is only one gene
for the trait but there are more than two
possible alleles.
Example of Multiple Alleles
Blood Type
• Blood type is an example of a common
multiple alleles trait. There are 3 different
alleles for blood type, (A, B and O)
• A is dominant to O. B is dominant to O and
AB is codominant These alleles are always on
the same chromosome in the same locus.
(location)
Blood cont.
• Blood type genotypes and phenotypes
• Phenotypes
O
A
B
AB
Genotypes
OO
AA or AO
BB or BO
AB
✔ Let’s Practice
• You are type O blood and you marry a person
with type AB blood. Complete the Punnett
Square to show your possible offspring below.
✔ Let’s Practice
• In the 1950’s, a young woman sued film
star/director Charlie Chaplan for parental
support for her child. Chaplan’s blood was AB,
mother’s was A and the son was O. Complete
the Punnett Square for the possible children
of Chaplan and the mother.
✔ Let’s Practice
• The judge ruled in favor of the mother and
Charlie Chaplan paid child support. Was the
judge correct? _______________
• Explain: ____________________________
•
____________________________
✔ Let’s Practice
• Suppose a newborn baby was accidently mixed up in the
hospital. DNA testing will take several days and is very
expensive. So the nurses have decided to help out by doing a
blood test.
• Baby 1 has blood type O, and baby 2 has blood type A
• Mr. Smith has type B and Mrs. Smith has type A
• Mr. Brown has type B and Mrs. Brown has type AB
• Complete Punnett Squares for each couple and find out who
the children belong to.
• HINT: You may have to do multiple Punnett Squares.
✔ Let’s Practice
✔ Let’s Practice
• You are type O blood and you marry a person
with type AB blood. Complete the Punnett
Square to show your possible offspring below.