Graded Assignment

1. Discuss how crossing-over leads to greater variability of phenotypes. Give an example to help explain your answer.

Answer:

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(Score for Question 2: ___ of 5 points)

2. Assume you are performing a cross between a plant that is heterozygous for the dominant traits red flowers and wrinkled seeds, with a plant that is homozygous for the recessive traits white flowers and smooth seeds. Assume the alleles are R for red flowers, r for white flowers, W for wrinkled seeds, and w for smooth seeds. The offspring of this cross show the following phenotypes:

 

43 red flowers and wrinkled seeds

 

7 red flowers and smooth seeds

 

9 white flowers and wrinkled seeds

 

41 white flowers and smooth seeds

 

What are the traits of the recombinant offspring in terms of flower color and seed shape? Explain how you know that these offspring are recombinant. What alleles would you expect to see in the individual chromosomes of each parent before and after crossing-over takes place? What is the recombination frequency? What is the distance between the genes in map units?

Answer:

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(Score for Question 3: ___ of 5 points)

3. What differences would you expect to see in a population made up of individuals whose chromosomes experience crossing-over frequently compared with a population made up of individuals whose chromosomes do not cross over? Explain your reasoning.

Answer:

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In pea plants, the allele for yellow seeds (Y) is dominant over the one for green seeds (y) and the allele for round seeds (R) is dominant over the one for wrinkled seeds (r). A homozygous yellow, round seed is crossed with a homozygous green, wrinkled seed. The offspring of this cross are then crossed. What is the probability that an offspring of the second generation will be green and wrinkled? (Express your answer as the simplest fraction.) _________

In Four-O' clock flowers, the gene R, for red flowers inincompletely dominant over the gene, W, for white flowers; theheterozygous plant bears pink flowers.
a) What color flowers are produced by the offspring of a crossbetween a red-flowered plant and a pink-flowered plant?
b) What are the genotypic and phenotypic ratios of the offspringproduced by crossing two pink-flowered plants?

1. A geranium from a true-breeding line with red flowers and hairyleaves (line A) is crossed to a geranium from a true-breeding linewith white flowers and smooth leaves (line B). The resultingoffspring, the F1, are all pink-flowered, with hairy leaves.

i) (three points) Suppose an individual from the F1 is crossedto an individual from line B. The resulting offspring, 1000individuals, are scored for flower traits. 249 have pink flowersand smooth leaves, 251 have pink flowers and hairy leaves, 253 havewhite flowers and smooth leaves, 247 have white flowers and hairyleaves. What type of allelic interactions are these? How many lociare involved? Are there multiple possibilities? Diagram a crossconsistent with the data.

ii) List and discuss several traits, in domestic plants of yourchoosing, that have a similar genetic basis.