Multiple Choice
Which of the following gametes can be formed from the genotype AaBb if AB and ab are linked?
4. Genetic Mapping and Linkage
Crossing Over and Recombinants
Back4. Genetic Mapping and Linkage
Crossing Over and Recombinants
- Multiple Choice
An experiment that was performed found the recombination frequency between two genes was 12.5%. What is the distance (in mapping units) between two genes?
- Multiple Choice
Which of the following terms describes two copies of the same chromosome?
- Open Question
Genes E and H are syntenic in an experimental organism with the genotype EH/eh. Assume that during each meiosis, one crossover occurs between these genes. No homologous chromosomes escape crossover, and none undergo double crossover. Are genes E and H genetically linked? Why or why not? What is the proportion of parental gametes produced by meiosis?
- Open QuestionWhy does more crossing over occur between two distantly linked genes than between two genes that are very close together on the same chromosome?
- Open QuestionExplain why a 50 percent recovery of single-crossover products is the upper limit, even when crossing over always occurs between two linked genes?
- Open QuestionWhy are double-crossover events expected less frequently than single-crossover events?
- Open QuestionWhat is the proposed basis for positive interference?
- Open QuestionWhat two essential criteria must be met in order to execute a successful mapping cross?
- Open Question
Alleles A and a are on one pair of autosomes, and alleles B and b are on a separate pair of autosomes. Does crossover between one pair of homologs affect the expected proportions of gamete genotypes? Why or why not? Does crossover between both pairs of chromosomes affect the expected gamete proportions? Why or why not?
- Open Question
You have isolated (1) a streptomycin-resistant mutant (strᴿ) of Chlamydomonas that maps to the chloroplast genome and (2) a hygromycin-resistant mutant (hygᴿ) of Chlamydomonas that maps to the mitochondrial genome. What types of progeny do you expect from the following reciprocal crosses?
mt⁺ strᴿ hygˢ× mt⁻ strˢ hygᴿ
mt⁺ strˢ hygᴿ× mt⁻ strᴿ hygSˢ - Open QuestionTwo different female Drosophila were isolated, each heterozygous for the autosomally linked genes b (black body), d (dachs tarsus), and c (curved wings). These genes are in the order d–b–c, with b being closer to d than to c. Shown here is the genotypic arrangement for each female along with the various gametes formed by both:Identify which categories are noncrossovers (NCOs), single crossovers (SCOs), and double crossovers (DCOs) in each case. Then, indicate the relative frequency in which each will be produced.
- Open QuestionIn Drosophila, two mutations, Stubble (Sb) and curled (cu), are linked on chromosome III. Stubble is a dominant gene that is lethal in a homozygous state, and curled is a recessive gene. If a female of the genotypeis to be mated to detect recombinants among her offspring, what male genotype would you choose as a mate?
- Open QuestionIf the cross described in Problem 18 were made, and if Sb and cu are 8.2 map units apart on chromosome III, and if 1000 offspring were recovered, what would be the outcome of the cross, assuming that equal numbers of males and females were observed?
- Open QuestionAre mitotic recombinations and sister chromatid exchanges effective in producing genetic variability in an individual? in the offspring of individuals?