Download a) Write the genotype probabilities.

Genetics Practice
Monohybrid (One-Gene)
· Genotype: combination of alleles in your DNA (i.e. GG)
· Phenotype: the trait that shows up based upon the genotype (i.e. green peas)
For each trait you have 2 alleles, one comes from each parent:
· Homozygous: two of the same alleles.
· Heterozygous: two different alleles.
The dominant allele BLOCKS the recessive allele (for ALL cases, unless labeled "mixed dominance")
Part I: First, lets practice some vocabulary.
Practice with terms. For all questions, use these facts: the trait is fur color (f). Black fur is dominant over
gray fur.
1. Write the letter of the dominant allele. _________
2. Write the letter of the recessive allele. _________
3. Write the genotype for gray fur (2 alleles!). _________
4. Write the genotype for Black fur (2alleles!). _________ or _________
5. Write out the homozygous dominant genotype. _________
6. Write out the heterozygous genotype. _________
7. Write out the homozygous recessive genotype. _________
8. Write the phenotype for #5. _________
9. Write the phenotype for #6. _________
10. Write the phenotype for #7. _________
Now, using a Punnett Square. Still using fur color, do the following problems.
1. If the mother is homozygous recessive and the father is
homozygous dominant.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
2. If the mother is heterozygous, and the father is heterozygous.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
3. If the mother is heterozygous, and the father is homozygous
dominant.
a)Write the genotype probabilities.
b) Write the phenotype probabilities.
4. If the mother is homozygous recessive, and the father is
heterozygous.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
Lets do some more Punnett Square practice using flower traits.
If you are experimenting with orchids, where red flowers are dominant over white flowers.
(Use the letter "R"). Make the following crosses:
1. Cross red homozygous orchids with white homozygous
orchids.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
2. Cross Red heterozygous orchids with heterozygous orchids.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
3. Cross homozygous recessive orchids with red heterozygous
orchids.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
4. Cross Red homozygous orchids with Red heterozygous
orchids.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
Now look lets look at people, using eye color. Brown eyes are dominant over blue/green.
(Use the letter "B"). Make the following crosses:
1. Mix two homozygous dominant parents together.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
2. Mix two heterozygous parents together.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
3. Mix a homozygous dominant mom with a heterozygous dad together.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
4. If Kevin has green (blue) eyes, and both his parents have brown eyes, what must
their genotypes be?
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
If you are experimenting with seagulls, where white feathers are dominate over grey feathers. (Use
the letter "W"). Make the following crosses:
1. If the mother is homozygous recessive, and the father is
homozygous dominate.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
2. If the mother is heterozygous, and the father is heterozygous.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
3. If the mother is heterozygous, and the father is homozygous
dominate.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
4. If the mother is homozygous recessive, and the father is
heterozygous.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
If you are experimenting with flies, where red eyes are dominate over white eyes. (Use the letter
"R"). Make the following crosses:
1. If the mother is heterozygous recessive, and the father is
homozygous recessive.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
2. If the mother has white eyes, and the father is heterozygous.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
3. If the mother is heterozygous, and the father is homozygous
dominant.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
4. If the mother is homozygous recessive, and the father is
heterozygous.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
Genetics Practice
Part II: Lets do some more Punnett Square practice using flower traits. This time, you are looking at
incomplete dominant traits.
If you are experimenting with roses, where red petals and white petals are incomplete dominant .
(Use the letter "R” for red and “W" for white). Make the following crosses:
1. Cross red homozygous roses with white homozygous roses.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
2. Cross Pink heterozygous roses with Pink heterozygous roses.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
3. Cross homozygous white roses with Pink roses.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
4. Cross Red homozygous roses with Pink roses.
a. Write the genotype probabilities.
b. Write the phenotype probabilities
Now for some practice using traits from people.
Now look lets look at people, using noses. Large noses and small noses are incomplete- dominant.
(Use the letter "N1" for large and the letter "N2" for small). Make the following crosses:
1. Mix two large nose parents together.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
2. Mix two medium nose parents together.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
3. Mix a medium nose mom with a large nose dad together.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
4. Mix a medium nose mom with a small nose dad together.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
Genetics Practice Part III: Now for more practice using traits from people.
Part IV: Ready for practice more Punnett Squares?
Genetics Practice IV
Are you now ready for a challenge?
"Sex-linked traits" come from genes that are located on the X chromosome, and not on the y.
(Remembers women are XX and men are Xy). For example, baldness is a recessive sex-linked trait.
Now you write the allele letter as a part of the X chromosome, like this:
XB or Xb; y stays blank.
The players: B is not bald, b is bald.
Genotype:
XBXB
XBy
XBXb
Xby
XbXb
Phenotype:
Not bald
Not bald
Not bald "carrier"
Bald
Bald
female
male
female
male
female
Example:
Crossing a not bald female with a bald male results in the following:
½ XBXb — Not bald carrier female.
½ XBy — Not bald male.
1. Cross (mate) a bald male to a carrier female.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
2. Cross a not bald male to a carrier female.
a) Write the genotype probabilities.
b) Write the phenotype probabilities.
If you’re a guy, which member of your family should you look at to tell if you are going to go bald?
Why? (Use a Punnett Square in your answer).
Are you now ready for that sex-linked gene challenge again?
"Sex-linked traits" come from genes that are located on the X chromosome, and not on the y.
(Remembers women are XX and men are Xy). For example, hemophilia is a genetic disorder where
a person can not form a blood clot. Hemophilia is a recessive sex-linked trait. Now you write the
allele letter as a part of the X chromosome, like this:
XH or Xh; y stays blank.
The players: H is not hemophiliac, h is hemophiliac.
Genotype:
XHXH
XHy
XHXh
Xhy
XhXh
Phenotype:
Not
Not
Not hemopilic
Hemopilic
Hemopilic
hemopilic
hemopilic
"carrier" female
male
female
female
male
1. Cross (mate) a carrier female with a male without hemophilia.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
2. Cross a carrier female with a male with hemophilia.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
3. Cross a female with hemophilia with a male without hemophilia.
a. Write the genotype probabilities.
b. Write the phenotype probabilities.
4. If you’re a guy, which member of your family should you look at to
tell if you have hemophilia? Why? (Use a Punnett Square in your
answer).