Genes and chromosome in genetics.

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Genes and chromosome in genetics. In Barbara McClintock and Harriet Creighton’s experiment with corn, there is eight possible progeny. What

is special about the corn with the colorless waxy (c/wx) phenotype? How else was the experiment confirmed
(Hint: how did they visually confirm the results)?
12. Genes A, B, and C are on a chromosome as shown below. Is this a physical or linkage map? Would you expect the distance between A and C to be more, less, or equal to the sum of the distance between each of
the outside markers and the middle gene (A-B + B-C)? Why?

13. Genes A, B, and C are on a chromosome as shown below. Is this a physical or linkage map? Would you
expect the percentage of recombination between A and C to be more, less, or equal to the sum of the recombination frequencies between each of the outside markers and the middle gene (AxB + BxC)? Why?

14. Why is crossing over between two genes on the same chromosome from 0% to 50%, and not higher?
15. Why is the linkage between two genes on the same chromosome from 50% to 100%, and not lower?
16. How many markers are necessary to map new genes to an exact location on the chromosomes described below using linkage?
a. 50 million base pair human chromosome b. 100 million base pair human chromosome
c. 150 million base pair human chromosome d. 200 million base pair human chromosome
e. 50 million base pair Drosophila chromosome
 

 

17. The examples below provide recombination frequency from two-factor crosses. Answer the following: a. For genes ABC, what is the gene order if AB = 30%, AC = 20%, and BC = 38%?
b. For genes XYZ (in order), XY = 25%, and YZ = 35%. Using the equation, what is the recombination frequency for the outside markers, XZ? Why is it not 60%?
c. For genes RST, what are the two possible gene orders if RS = 20%, and ST = 10%? What do you need to know to determine which is correct?
18. Two Drosophila with genotypes AABBCC and aabbcc are crossed to produce a heterozygous offspring,
AaBbCc (the gene order is unknown). This AaBbCc Drosophila is crossed with an aabbcc Drosophila, resulting in the offspring below:
Number: Phenotype:
600 ABC and abc 200 AbC and aBc
150 ABc and abC 50 Abc and aBC
a. Which phenotypes represent the single crossovers?
b. Which phenotypes represent the double crossovers? c. What is the gene order?
d. What does phenotype AbC represent? e. What does phenotype ABc represent?
19. Why were the organisms of classical genetics insufficient for deeper analysis, and what replaced them?