4. Genetic Mapping and Linkage

In this chapter, we focused on linkage, chromosomal mapping, and many associated phenomena. In the process, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions? When designed matings cannot be conducted in an organism (for example, in humans), how do we learn that genes are linked, and how do we map them?

In this chapter, we focused on linkage, chromosomal mapping, and many associated phenomena. In the process, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions? How do we know that sister chromatids undergo recombination during mitosis?

In this chapter, we focused on linkage, chromosomal mapping, and many associated phenomena. In the process, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions? How do we know that crossing over results from a physical exchange between chromatids?

In this chapter, we focused on linkage, chromosomal mapping, and many associated phenomena. In the process, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions? How do we know that specific genes are linked on a single chromosome, in contrast to being located on separate chromosomes?

In this chapter, we focused on linkage, chromosomal mapping, and many associated phenomena. In the process, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions? How was it established experimentally that the frequency of recombination (crossing over) between two genes is related to the distance between them along the chromosome?

In a diploid species of plant, the genes for plant height and fruit shape are syntenic and separated by 18 m.u. Allele D produces tall plants and is dominant to d for short plants, and allele R produces round fruit and is dominant to r for oval fruit. A plant with the genotype DR/dr produces gametes. Identify gamete genotypes, label parental and recombinant gametes, and give the frequency of each gamete genotype.

Write a short essay that discusses how crossing over can be detected and how the resultant data provide the basis of chromosome mapping.

Describe the cytological observation that suggests that crossing over occurs during the first meiotic prophase.

The genes dumpy (dp), clot (cl), and apterous (ap) are linked on chromosome II of Drosophila. In a series of two-point mapping crosses, the following genetic distances were determined. What is the sequence of the three genes? dp–ap 42 dp–cl 3 ap–cl 39

A small population of deer living on an isolated island is separated for many generations from a mainland deer population. The populations retain the same number of chromosomes but hybrids are infertile. One chromosome (shown here) has a different banding pattern in the island population than in the mainland population. Describe how the banding pattern of the island population chromosome most likely evolved from the mainland chromosome. What term or terms describe the difference between these chromosomes?

Drosophila melanogaster has one pair of sex chromosomes (XX or XY) and three pairs of autosomes, referred to as chromosomes II, III, and IV. A genetics student discovered a male fly with very short (sh) legs. Using this male, the student was able to establish a pure breeding stock of this mutant and found that it was recessive. She then incorporated the mutant into a stock containing the recessive gene black (b, body color located on chromosome II) and the recessive gene pink (p, eye color located on chromosome III). A female from the homozygous black, pink, short stock was then mated to a wild-type male. The F₁ males of this cross were all wild type and were then backcrossed to the homozygous b, p, sh females. The F₂ results appeared as shown in the following table. No other phenotypes were observed. Wild Pink* Black, Black, Pink, Short* Short Females 63 58 55 69 Males 59 65 51 60 *Other trait or traits are wild type. Based on these results, the student was able to assign short to a linkage group (a chromosome). Which one was it? Include your step-by-step reasoning.