Biology 1001A Lecture Notes - Lecture 5: Sister Chromatids, Mendelian Inheritance, Product Rule

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29 Aug 2016

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Lecture 10: characteristics of mendel"s work that set him apart as a genetic researcher. Mendel used pea plants and used an experimental approach to genetics, rather than a theoretical approach. And used a radical mathematical analysis: components of mendel"s explanatory model. Mendel pure-bred white and pink pea plants for several generations until they were true- breeding, then he cross bred the parent generation to observe the phenotype of the f1 generation. He discovered that in the f1 generation, all the offspring had pink flower, while in the f2 generation, pink: white was 3:1 ratio: distribution of progeny (offspring), given parental genotypes in monohybrid (2 heterozygous) and sex-linked crosses. Monohybrid: dominant to recessive is 3 to 1 ratio. In sex-linked crosses, 1:1 for m:f: location of various alleles on homologues. Alleles of a gene are present at the same loci on homologous chromosomes, since the location of the genes are at the same location: segregation of various alleles during meiosis.

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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)

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11. You suspect that two genes interact with one another to determine the product of a pathway you are studying. You cross two pure breeding plantsâone with white flowers and one with pinkâto make F1 individuals that have blue flowers. You cross the F1 generation and observe the following numbers of individuals with different phenotypes: Number of individuals Phenotype 91 Blue 30 Pink 39 White Which pathway best explains these results? (Note that arrows indicate enzymatic reactions carried out by products of genes 1 and 2. Assume that buildup of metabolites will determine flower color.)

Question 12 and 13: Consider the biochemical pathway presented below. This pathway determines pigment production in pea flowers. (Note: gene products are required for each reaction to proceed.)

12. Do you expect that genes A and B will interact with one another?

A. Yes B. No C. Insufficient information to determine

13. What phenotype ratio would you expect in offspring produced by crossing AaBb parents?

A. 9:3:3:1 (blue : green : yellow : white) B. 9:3:4 (blue : green : white) C. 9:7 (blue : white) D. 15:1 (blue : white)

14. How can haplosufficiency explain dominance of an allele that codes for a functional protein over a null (loss of function) allele?

A) a single functional copy of the gene produces sufficient gene product for normal biological function B) a single functional copy of the gene produces insufficient gene product for normal biological function C) the null allele produces a product that interferes with proper function of the normal allele D) the null allele produces a product that does not interfere with proper function of the normal allele E) the null allele rapidly mutates to reacquire normal functionality

15. In a plant species with genes A and B, you have isolated recessive mutant alleles at each locus, which you call a and b. You would like to know whether these two genes are linked. To test this hypothesis, you obtain an individual that is heterozygous at both genes (AB/ab) and perform a test cross. Which results would be most consistent with these loci being tightly linked? (Results are counts of the numbers of offspring from the testcross.)

A. Ab/ab 390 aB/ab 410 AB/ab 350 ab/ab 420

B. Ab/ab 80 aB/ab 73 AB/ab 760 ab/ab 754

C. Ab/ab 700 aB/ab 695 AB/ab 56 ab/ab 59

D. Ab/ab 400 aB/ab 65 AB/ab 50 ab/ab 659

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Biology 1001A Lecture Notes - Lecture 5: Sister Chromatids, Mendelian Inheritance, Product Rule

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