QUESTION 8 This question is chalenging. You will not have one this hard on the e

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QUESTION 8 This question is chalenging. You will not have one this hard on the exam, but it s good practice to see if you understand the main concepts of genetics.)You study the phenotypes of two characteristics controlled by two gene ocl that are very close together (ess than 0.1 cent Morgan) on one pea plant chromosome. One gene is for rough leaves, which is dominant to smooth leaves. The other is for thick stems, which is dominant to thin stems. When you do a dihybrid cross of a true-breeding plant with rough leaves and thlck stems to a true-breeding plant with smooth leaves and thin stems, you would expect the F2 generation to have a less than 1 in 1000 plants with thin stems and rough leaves. b.mostly plants with smooth leaves and thick stems. G mostly plants with rough leaves and thin stems. d mostly plants with smooth leaves and thin stems G equal numbers of plants with rough leaves and smooth leaves QUESTION 9 Many genes are involved in determining skin color in humans. This aspect of the genetic control of skin color is an example of 8. a polygenic trait b a plelotropic gene C. a gene d. epistass e. a sex-linked gene with three or more alleles QUESTION 10 Green pod color (G) is dominant to yellow pod color (g). Which of the following genotypes could be for a plant with yellow pods? a GG b.Gg or GG C. d.gg e gg or GG lick Sauve and Submit to save and submit. Click Save AU Answers to save all answers.

Explanation / Answer

Assume that Thick stem - T; thin stem = t
Rough-leaf = R; smooth leaf = r
T is dominant to t
R is dominant r.
Now, the true breeding plants are crossed =
RRTT   x   rrtt
RT    x      rt   gametes
F 1 = RrTt = Rough leaf and thick stem.

Now, in F2: RrTt    x     RrTt

We can get all possible 16 combinations in the ratio 9:3:3:1 like a dihybrid cross. However, the genes Rough and thickness are liked by 0.1 cM. This means they tend to remain together most of the time and very less recombination can occur. This means most plants will be rough thick like F1 parents and very few (0.1) will be recombinants like rough thin or smooth thick. So option 1 is right, less than 1 in 1000 will be thin rough.

9. Ans: Polygenic trait.
Polygenic means a character is coded by multiple genes.
Pleiotropic means a single gene can affect more than one phenotype. it is the reverse of polygenic. Epistatic means one gene influencing the expression of another gene. Sex-linked means the genes carried on X chromosome.

10. G is dominant to g.
The presence of at least one copy of G will make the pods Green. So GG and Gg combinations are green. Since the allele g is recessive in nature it should occur in two copies to impart the yellow colour, so gg = yellow.
Ans: d = gg.

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