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BIO 161 Chapter Notes - Chapter 14: Y Chromosome, Punnett Square, Gregor Mendel

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18 Aug 2016

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Objectives: give two examples of monohybrid crosses performed by gregor mendel. They have two children, a normal boy and girl. They have a daughter with pku: a dihybrid cross is performed between a pea plant with round, yellow peas and a plant with green wrinkled peas. What is the dominant allele for pea color and pea shape: what gametes and in what proportions could be made by the f1 pea plant described above (assuming independent assortment). Draw and fill in a punnett square that shows the f2 generation. What f2 phenotypes would appear and in what proportions: give one example of codominance. It is important that you extend your understanding of genetics by working to solve genetics problems. There are 26 questions with solutions at the end of chapter 14. It is important that you try to solve these problems.

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Related Questions

You recently discovered a new variety of sweetpea plants in the area surrounding Chernobyl that cannot be crossedwith the sweet pea plants used in Mendel's experiments. Youidentify several pure breeding strains with characteristics thatare similar to those described by Mendel. You found that round (R)was dominant over wrinkled (r) for pea shape and yellow (Y) wasdominant over green (y) for pea colour in monohybridcrosses.

(a) show the expected outcome of a dihybridcross starting with pure breeding plants with round yellow peas andpure-breeding wrinkled green peas. Include all phenotypes and thecorresponding genotypes for parental, F1 and F2 generations. Alsoinclude the expected phenotypic ratios for the F2 generation.Surprisingly, when you performed this cross, you notice someinteresting differences from Mendel's experiments. Although all F1progeny had round yellow peas, the F1 self cross resulted in farfewer round green and wrinkled yellow peas than expected. Beingvery clever, you hypothesize that these loci may be linked in thisvariety of pea and you performed a testcross between F1 plants anddouble homozygous plants with wrinkled green peas. You obtained thefollowing progeny: 445 Round yellow, 48 round green, 52 wrinkledyellow and 455 wrinkled green. (b) Identify the parental andrecombinant classes from the test cross (2 marks). (c) Estimate therecombination frequency using these data, and show your work. (d)Indicate the distance between loci in map units, and show yourwork. (e) Using the recombination frequency you calculated in (c),predict the phenotypic ratio in the F2 generation in the dihybridcross in (a)

Problem A. You cross two homozygous parents: RRYY (round yellow) and rryy (wrinkled green) to produce an F1 generation. Round seeds are dominant, yellow seeds are dominant. You cross two F1s to produce the F2 generation. In the F2 generation, you find an individual with round yellow seeds. You do a testcross to find out the genotype of this âmysteryâ dominant/dominant phenotype. In the offspring of the cross, you find 1?2 have round yellow seeds and 1?2 have wrinkled yellow seeds.

1. Based on these data what was the genotype of the mystery F2?

Problem B. You carry out a dihybrid cross between a red-flowered rose with long pollen grains (A1A1 LL) and a white-flowered rose with round pollen (A2A2 l l). The flower color gene (A) shows incomplete dominance, and long pollen is completely dominant to round pollen. The genes for these traits are on different chromosomes so assort independently

2. What would be the phenotypes of the F1 generation?

3. What fraction of the F2 generation is expected to have red flowers and long pollen? (As always when traits are independent, what rule can you apply to save time?)

Problem D. In the example of epistasis presented in class, the agouti allele in mice (A) codes for striped hairs and is dominant to the allele for all black hairs (a). A loss-of-function allele for the pigment gene (b) produces no pigment and is recessive to the normal, dominant allele (B). The recessive allele at b masks the effect of the A gene. A dihybrid cross of AABB and aabb is carried out.

5. Name all of the genotypes in the F2 generation that can produce an albino (no pigment) phenotype.

Problem E. A cross is made between homozygous fruit flies that differ for eye color (the st gene) and

body color (the e gene). The F1 double heterozygote is shown below using chromosome notation.

--------------------------------------

st = the recessive allele for scarlet eyes; st+ = the dominant wildtype allele for red eyes e = the recessive allele for ebony body; e+ is the dominant wildtype allele for gray body

6. Are the chromosomes shown in the genotype above in cis or trans configuration?

7. Based on this notation, what were the genotypes and phenotypes of the two parents of the F1? (Think carefully here...)

8. With what phenotype would you cross this F1 to measure recombination frequency?

7. When a pea plant of genotype Aa Bb produces gametes whatproportion will be ab?

8. Hamsters are long haired if they have the genotype LL or Ll andthey are short haired if they have the genotype ll. A long hairedhamster is mated with a short haired hamster. Half of the offspringare long haired and half are short haired. This allows us toconclude that the long haired parent hamster is? D

9. In peas yellow seed (Y) is dominant over green seeds (y) andtall plant (T) is dominant over short plant (t) .Calculate theprobability of the genotypes and phenotypes. in the F2 generationof a dihybrid cross that begins when a dominant homozygote iscrossed with a recessive homozygote. You must show the all of theprobability calculations. D

10. In a fruit fly experiment, two gray-bodied fruit flies producemostly gray-bodied offspring, but some of the offspring have blackbodies. If there are 280 offspring, how many will you predict willhave grey bodies and how many will have black bodies? How many ofthe 280 offspring do you predict will be heterozygous? Show yourwork. D

11. In a dihybrid cross AaBb X AaBb what fraction of the offspringwould be D

i) homozygous for both recessive traits
ii) heterozygous for both traits
ii) homozygous for both traits

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