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 basics 1. Determine the genotypes of the parent organisms Ex: cross two heterozygous red flowers. White is the recessive phenotypeheterozygous 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 RRRr rr Rr rr Rrrr

That’s not the one… Let’s go look at that again

Dominant – recessive problem In humans, being able to roll your tongue is dominant over not rolling. Which square shows the possible children of two parents who are heterozygous for tongue rolling. T t T T T T t T 25% homozygous roller 100% homozygous roller 50% heterozygous roller 25% homozygous non-roller TTTt tt TT

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 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 F1 will be 100% homozygous brown and F2 will be 75% brown and 25% white – All offspring in both generations will be brown 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 BBBb 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. All offspring in both generations will be green. – F1 will be 100% green and F2 will be 75% green and 25% tan F1 will be 100% green and F2 will be 75% green and 25% tan – F1 will be heterozygous green and F2 will be all tan F1 will be heterozygous green and F2 will be all tan

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 100% will be pink – 50% will be red and 50% will be white 50% will be red and 50% will be white – 25% will be red, 25% will be white and 50% will be pink 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 red 50% heterozygous pink 25% homozygous white Try another one RRRr 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 tan – All offspring will be brown All offspring will be brown – 50% will be tan and 50% 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 All of the boys will be colorblind but none of the girls – 50% chance for any child 50% chance for any child – 50% chance for boys and 25% for girls 50% chance for boys and 25% for girls

That’s not the one… Let’s look at the square. Dad’s genotype is X r Y and mom’s is X R X r, so the punnett square looks like this X r Y X R This girl and boy are NOT affected X r This girl and boy ARE colorblind So there is a 50% chance that any child will be color blind regardless of gender. X R X r XRYXRY X r X r 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 50% chance for any child – 100% for the boys, 0% for the girls 100% for the boys, 0% for the girls – 100% for the girls, 50% for the boys 100% for the girls, 50% for the boys

More practice problems available Check out these websites for more genetics practice problems: In your textbook, chapter 10 and 11 have more information