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GENETICS REVIEW PRACTICE
You can do it!!
Where do you need to start?
• Punnett square basics• Dominant-recessive practice problems• F1 and F2 problems• Incomplete dominance problems• Sex-linked problems• More practice on-line
I’m ready for the test!!
Punnett square basics1. Determine the genotypes of the parent organisms
Ex: cross two heterozygous red flowers. White is the recessive phenotype
2. Write down your "cross" (mating) Ex: Rr x Rr
3. Draw a punnett-square
4. “Split" the letters of the genotype for each parent & put them "outside" the p-square R r R r
Punnett square basics (cont.)5. Determine the possible genotypes of the offspring by filling in the p-square
R r R 25% homozygous red (RR) 50% heterozygous red (Rr) r 25% white (rr) Now you try one.Problem: If red flowers are dominant over white flowers. Which punnett square shows the cross between a homozygous red flower and a white flower? R R R r r r
r r
100% heterozygous red 50% heterozygous red 50 % white
RR Rr
Rr rr
Rr Rr
Rr Rr
Rr rr
Rr rr
Awesome!!
• What else do you need to practice?
F1 and F2 problems• If brown is dominant over white feathers in
chickens, what will the F1 and F2 ratios be when a homozygous brown chicken is mated with a white chicken?– F1 will be 100% homozygous white and F2 will be
50% heterozygous brown and 50% white– F1 will be 100% homozygous brown and F2 will be
75% brown and 25% white– All offspring in both generations will be brown
That’s not the one…Let’s look at the punnett squares:
When a homozygous brown chicken is mated with a white chicken:
F1 B B F2 B b b B
b b
100% heterozygous brown 75% brown 25% white
Bb Bb
Bb Bb
BB Bb
Bb bb
Let’s try another F1 and F2 problem
• If green is dominant over tan skin in frogs, what will the F1 and F2 ratios be when a homozygous green frog is mated with a tan frog?– All offspring in both generations will be green.– F1 will be 100% green and F2 will be 75% green an
d 25% tan– F1 will be heterozygous green and F2 will be all ta
n
Incomplete Dominance
• In carnations, red and white colors show incomplete dominance. The heterozygous form is pink. What are the expected phenotypes in a cross between two pink carnations?– 100% will be pink– 50% will be red and 50% will be white– 25% will be red, 25% will be white and 50% will be pink
That’s not the one…• Let’s look at the square. The genotype for pink
is Rr so the square is R r R r
25% homozygous red50% heterozygous pink25% homozygous white
Try another one
RR Rr
Rr rr
Incomplete Dominance
• In horses, brown and white colors show incomplete dominance. The heterozygous form is tan. What are the expected phenotypes in a cross between a brown and a tan horse?– All offspring will be tan– All offspring will be brown– 50% will be tan and 50% will be brown
Sex-linked genetics
• In humans, color blindness is a recessive, sex-linked condition. If a colorblind man marries a woman who is a carrier, what are the chances that their children will be colorblind?– All of the boys will be colorblind but none of the girls– 50% chance for any child– 50% chance for boys and 25% for girls
That’s not the one…• Let’s look at the square. • Dad’s genotype is Xr Y and mom’s is XR Xr , so
the punnett square looks like this• Xr Y• XR This girl and boy are NOT affected
• Xr This girl and boy ARE colorblind
• So there is a 50% chance that any child will be color blind regardless of gender.
XR Xr XRY Xr Xr Xr Y
Sex-linked genetics
• In humans, hemophilia is a recessive, sex-linked condition. If a man who does not have hemophilia marries a woman who has the disease, what are the chances that their children will have hemophilia?– 50% chance for any child– 100% for the boys, 0% for the girls– 100% for the girls, 50% for the boys
More practice problems available• Check out these websites for more genetics
practice problems:
http://www.hobart.k12.in.us/jkousen/Biology/psquprac.htm
http://biology.clc.uc.edu/courses/bio105/geneprob.htm
In your textbook, chapter 10 and 11 have more informationhttp://jgadow.wikispaces.com/Academic+Biology+Home