D34299-Genetics Worksheet

D34299-Genetics Worksheet - Genetics Worksheet Part 1...

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Page #1 Genetics Worksheet Part 1 Introduction: 1. Describe the genotypes given (use your notes). The first two are already done. A. DD homozygous, dominant D. ss ______________________ B. Dd _ heterozygous E. Yy ______________________ C. dd __________________ F. WW ____________________ 2. In humans, brown eye color (B), is dominant over blue eye color (b). What are the phenotypes of the following genotypes? In other words, what color eyes will they have? A. BB ________________________ B. bb ________________________ C. Bb ________________________ The Five (5) Steps Associated With Solving a Genetics Problem: If you take the time to follow the directions below, you will be able to solve most genetics problems. 1. Determine the genotypes of the parents or whatever is given in problem. 2. Set up your Punnett square as follows: *# sq. based on possible gametes that can be formed. possible parental gametes Possible parental gametes Other possible parental gametes 3. Fill in the squares. This represents the possible combinations that could occur during fertilization. 4. Write out the possible genotypic ratio of the offspring. 5. Using the genotypic ratio determine the phenotypic ratio for the offspring. . Part 2: Sample Problem (Just read this over, it is a practice problem) A heterozygous male, black eyed mouse is crossed with a red eyed, female mouse. Predict the possible offspring! Step 1 : Determine the genotype of the parents . The male parent is heterozygous which means he has one allele for black eyes and one allele for red eyes. Since his eyes are black, this means that black allele must be dominant over the red allele. So the male parents genotype is “ Bb” (B = allele for black eye, b = allele for red eye). The female parent has red eyes, there is only one way to have this recessive phenotype, so she must to be homozygous recessive. Homozygous recessive means that her genotype must be bb ”. Therefore, genotype of the parents is Bb x bb.
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Page #2 Step 2: During meiosis (the formation of sex cells) one member (allele) of each gene pair separate. The male mouse (Bb) produces some sperm containing “B” (the allele for black eye) and some sperm containing “b” (the allele for red eyes). On one axis of the Punnett square you put the two possible gametes for the male. B b b b Repeat this for the other axis for the possible female gametes. Since she is “bb” you must put “b” and “b”. Step 3: During fertilization sperm meets the egg. The Punnett square show us the various possibilities during fertilization. The offspring must be one of these genotypes listed in the squares. B b b b Bb If the sperm contains a “B” and it fertilizes an egg containing the “b” allele, the resultant offspring will have the genotype “Bb”. Repeating the process we can see all of the possible genotypes. B b b b Bb Bb bb bb Step 4: The genotypic ratio is determined by counting each possible genotype. You’ll note there are two “Bb” for every two “bb”. Therefore, we write the ratio as 2 : 2 Bb : bb Possible Sperm Possible Eggs
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Page #3 Normally we reduce to the lowest terms: 1 : 1 Bb : bb Step 5: The Bb will produce a black eyed mouse (phenotype) and the bb will produce a red eyed mouse (phenotype). The phenotypic ratio is written as
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