Two indpendently assorted genes control the color and taste of blueberries. Expr
ID: 8263 • Letter: T
Question
Two indpendently assorted genes control the color and taste of blueberries. Expression of the dominant allele B results in blue color while expression of the recessive allele b results in white color. Similarly, expression of the dominant allele T results in tasty berries while expression of the recessive allele t results in tasteless berries. An individual with genotype BB TT is crossed with an individual that is homozygous recessive bb tt for both traits.A. What will the genotype(s) of the F1 generation be?
B. If two individuals from the F1 generation were crossed, what would be the phenotypic ratios of the F2 generation?
(Please provide step by step work and reasoning for each problem) Thank you!
Explanation / Answer
The F1 generation gets one gene from each parent. Homozygous means that both letters (genes) are the same. It has identical alleles. So the F1 generation will all be Bb Tt - no possible variation there. You could draw the box with one parent across the top and one down the side, but it would be quite boring. The variation occurs in the F2 generation. There are four possible combinations of the two genes for each parent. They are written out at the top and side of the first table below. The offspring get one allele from each parent F2 TB Tb tB tb TB TT BB TT Bb Tt BB Tt Bb Tb TT Bb TT bb Tt Bb Tt bb tB Tt BB Tt Bb tt BB tt Bb tb TtBb Tt bb tt Bb tt bb F2 Mom Mom Mom Mom Dad 1 2 3 4 Dad 5 6 7 8 Dad 9 10 11 12 Dad 13 14 15 16 There are sixteen possible outcomes each of which has an equally likely chance of occuring. Odds are: 1/16 is homozygous dominant in both traits (box one). 1/16 homozygous recessive in both traits (box 16) [These aren't phenotypes since we can only observe Tasty or Blue, not that it is homozygous] Odds are four of the sixteen (1/4) will be tasteless (Boxes 11, 12, 15, 16) Odds are four of the sixteen (1/4) will be white (Boxes 6, 8, 14, 16) Since odds add up to one, 3/4 will be tasty (Boxes 1,2,3,4,5,6,7,8,9,10,13,14) and 3/4 will be blue (Boxes 1,2,3,4,5,7,9,10,11,12,13,15) Odds are that 9/16 will be both blue and tasty (Boxes 1,2,3,4,5,7,9,10,13) Odds are 7/16 that member of F2 generation will either be white, tasteless or both. Odds are 6/16 or 3/8 that individual will be either white or tasteless, but not both.
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