Many of the traits examined by Mendel in his dihybrid crosses are now known to b

Question

Many of the traits examined by Mendel in his dihybrid crosses are now known to be encoded by genes that occur on the same chromosome. Given the outcome of his experiments, what can you infer about the distance between these genes? How would his results have been different if the traits examined had included plant height and pod shape, which are encoded by genes that are very close together on the same chromosome? Use the following terms in your response: alleles; loci; recombination; expected ratio.

2. The genes curved (c, curved wings) and plexus (px, extra wing veins) are linked on the second chromosome in Drosophila. The progeny with the following genotypes are recovered from a standard test cross: cpx/cpx 84 c+/cpx 400 ++/cpx 96 +px/cpx 420 a) What are the genotypes of the parents of this test cross? Specify both chromosomes of the wild type parent and state whether the curved and plexus mutant alleles are in repulsion linkage or in coupling linkage. b) Give the map distance in centiMorgans between these two loci. (Show your work) (Note: the numbers will be changed for your test.)

3. Evolutionary theory predicted that bacterial resistance to antibiotics would evolve. Given time and sufficient heritable variability, living organisms (including bacteria) will evolve when a selective pressure (like an antibiotic) is introduced. But evolutionary theory also gives doctors and patients some specific strategies for delaying even more widespread evolution of antibiotic resistance. Some of these strategies are given below: -Don't use antibiotics to treat viral infections. -Avoid mild doses of antibiotics over long time periods. -When treating a bacterial infection with antibiotics, take all your pills. -Use a combination of drugs to treat a bacterial infection. -Reduce or eliminate the "preventive" use of antibiotics on livestock and crops. For each strategy, give a justification based on your knowledge of bacteria and evolution, why this strategy would reduce the transmission of antibiotic resistance.

4. What are the five assumptions that are made about a population that is in Hardy-Weinberg equilibrium? Detail how violations of each assumption can alter the frequency of genotypes in a population from HW expectations. A complete answer will indicate whether violating the assumption is likely to consistently increase the frequency of homozygous or heterozygous individuals and explain how this happens. (Note: You will be given one or two assumptions in the test but you must be prepared to answer for any of them.) 5. What conditions are necessary for natural selection to operate? Name and explain how each condition contributes to natural selection.

6. Snapdragon flowers exhibit incomplete dominance in flower colour such that Rr individuals have pink flowers, rr have white flowers, and RR have red flowers. You encounter a population of flowering snapdragon and count 2 individuals with white flowers, 32 individuals with pink flowers, and 16 individuals with red flowers. (Note: the numbers will be changed in your test.) If the population were in Hardy-Weinberg equilibrium, how many pink individuals would you expect to find in a sample of 50 plants? What are two distinct hypotheses (other than population size) that could be used to explain your observation (that is, the difference between what you observe and what you expect)?

7. Sickle cell anaemia: The selective forces that a population experiences can vary by context, especially by geographic place. a) Explain in your own words how natural selection affects the evolution of haemoglobin in humans and how and why the selective pressures differ among human populations. b) For your answer to part a, which are examples of disruptive, stabilizing or directional selection? c) For human populations living in regions of the modern world without malaria, do you expect the HS allele to eventually go extinct? Explain.

8. You are given two true breeding lines of mice, one has solid black fur and the other is albino. You cross the lines and all F1’s have agouti coloration (light brown fur). You cross the F1’s with themselves and in your F2 generation observe a mixture of agouti, black, and albino coloration. About 56% of your F2 mice are agouti, 19% are black, and 25% are albino. Provide a detailed hypothesis explaining this result including your proposed genotypes for the original lines, the F1’s and the F2’s.

9. Famously, Queen Victoria’s descendants were plagued by haemophilia, an X-linked recessive disease. The present day monarch of the United Kingdom, Queen Elizabeth, is a direct descendent of Queen Victoria: Elizabeth’s great grandfather was Victoria’s son (King Edward VII) who was not a haemophiliac. What is the chance that Elizabeth is a carrier for haemophilia? Explain your reasoning.

10. If 15% of men in a population are colour blind, what frequency of colour blind women would you expect in this same population?

11. In a hypothetical species of butterfly, wing spots are controlled by a single locus where BB individuals have blue spots, YY individuals have yellow spots, and BY individuals have green spots. Ten years ago, a previous collector randomly collected 1000 butterflies and reported finding 90 blues, 420 greens, and 490 yellows. You collect 40 blues, 320 greens, and 640 yellows. Has there been evolution in this population? If yes, is natural selection involved? Explain and justify your answers.

12. You have been cultivating snapdragons in your garden and allowing plants to re-germinate each year from seeds dropped by the previous year’s annual plants. You know that white flowers are recessive and count 9 white flower plants out of 100 that you examine. Do you find evidence for evolution acting in your population? If yes, could natural selection be involved?

13. Thalassemia is blood disorder where individuals with thalassemia produce too much iron. This disease is inherited as an autosomal recessive. It has been hypothesized that heterozygous individuals have some immunity to malaria (similar to sickle cell anaemia). You obtain blood samples from a Mediterranean population of humans where malaria is endemic and among 100 individuals find 3 with thalassemia and 50 who are carriers. Are these results consistent with the hypothesis that heterozygous individuals have partial immunity to malaria?

14. Human genetic diseases are more frequently found in small isolated populations. Drawing upon your knowledge of evolution, explain this observation.

15. Governments, industry, and environmental organisations all have invested in global seed banks. What are seed banks and why would it be in the best interest of such disparate organisations to fund them?

16. You want to breed Labrador dogs and want to produce a full litter of chocolate (brown) labs. Remembering that there are three possible phenotypes for Labrador coat colour (black, yellow, and chocolate), what genotypes (and their accompanying phenotypes) will always yield only brown puppies? Will all crosses based on those phenotypes always give you brown puppies?

Explanation / Answer

Answer for the first question:

In the dihybrid cross of the Mendel, he discovered alleles that are responsible for two different traits. The two genes studied by Mendel in his experiments were far apart from each other. This is proved by the law of segregation and law of independent assortment. The separation of the alleles and the recombination is well understood by these laws, which shows that the alleles are far apart and are not linked. That is why Mendel obtained the ratio of 9:3:3:1.

The results if included the plant height and pod shape in his experiments, the ratios would have been different. The recombination frequency would be quite low as the genes are linked and occur on the same chromosome. This means the genes would not assort independently because they are closer to each other.

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