B1 alleles working out eye colour


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B1 alleles working out eye colour

  1. 1. Phenotype - Will I look like my mum or my dad? Part 1 Introduction: 1. Describe the genotypes given (use your notes). The first two are already done. A. DD homozygous, dominant B. Dd heterozygous C. dd __________________ E. Yy ______________________ D. ss ______________________ F. WW ____________________ Image source: http://www.abpischools.org.uk/page/modules/genome/dna2.cfm?coSiteNavigation_allTopic=1 2. In humans, brown eye colour (B), is dominant over blue eye colour (b). What are the phenotypes of the following genotypes? In other words, what colour eyes will they have? A. BB ________________________ B. bb ________________________ C. Bb ________________________The alleles for blue eyes are: The alleles for brown eyes are: Source: http://en.wikipedia.org/wiki/File:Eye_iris.jpg#file  or  Source: http://en.wikipedia.org/wiki/File:Menschliches_auge.jpg
  2. 2. Part 2 How to solve genetic problems using Punnett square #Learn these 5 steps carefully.If you take the time to follow the directions below, you will be able to solvemost 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 gametesthat can be formed. Possible parent gametes (mother’s egg cells) Other possible parent gametes (father’s sperm cells)3. Fill in the squares. This represents the possible combinations that couldoccur during fertilization.4. Write out the possible genotypic ratio of the offspring.5. Using the genotypic (gene) ratio determine (work out) the phenotypic (thetype/features that show up) ratio for the offspring.Now go to the next page and work out the chances of anoffspring/child inheriting certain eye colours.
  3. 3. What are the chances of a child having blue eyes?In humans, brown eye allele (B) is dominant over blue eye allele (b).A homozygous dominant (BB) or heterozygous (Bb) offspring/child will havebrown eyes. A homozygous recessive (bb) child will have blue eyes.A heterozygous woman marries a homozygous recessive man.1. Work out the genotypes of the parents (parent’s genes).Mother Father 2. Set up a Punnett square with possible gametes (sex cells).Explanation 1: During meiosis (the formation of sex cells) one member (allele) of eachgene pair separate. In this example, the male (Bb) produces some sperm containing“B” (the allele for brown) and some sperm containing “b” (the allele for blue). Fill in the circles only and go to step 3.3. Fill in the Punnett squares above to work out the possible combination forthe offspring.Explanation 2: During fertilization sperm meets the egg. The Punnett square show usthe possible combination of genes during fertilization.4. Count the number of possible genotypes.  Number of BB = ______  Number of Bb = ______  Number of bb = ______5. What is the predicted phenotypic ratio for the offspring? What shows up?  Number of brown eyes child/offspring = ______  Number of blue eyes child/offspring = ______