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GENETICS REVIEW PRACTICE You can do it!!

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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!!

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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

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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

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

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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

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Awesome!! What else do you need to practice?

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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 information http://jgadow.wikispaces.com/Academic+Biology+Home

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