Exam 9: The Locations of Genes on Chromosomes: Linkage and Genetic Maps

Which of the following statements about double-crossovers are true? Please select all that apply.

A cross between two true-breeding strains (P₀ generation) with genotypes A/A;b/b and a/a;B/B results in an F₁ genotype of A/a;B/b. If this is test-crossed to a/a;b/b, which of the following offspring have parental phenotypes? Please select all that apply.

A Drosophila fly heterozygous for alleles for black body, dumpy wings, and purple eyes was test-crossed to a fly that was homozygous recessive for all three genes. The genes are all on the same chromosome. The offspring had the following phenotypes in the following numbers: Phenotype Number of offspring wild type 225 black body, purple eyes, dumpy wings 238 dumpy wings 122 black body, purple eyes 135 black body, dumpy wings 15 purple eyes 19 purple eyes, dumpy wings 6 black body 5 What is the order of the genes on the chromosome?

What is a tetrad

A series of crosses to test whether two genes in Drosophila flies are sex-linked and on the same chromosome, and which alleles are dominant, are described below. Match each conclusion with the piece of evidence supporting it. A cross between a true-breeding black, apterous (no wings) female parent and a true-breeding wild-type male parent produced 100% F₁ offspring with wild-type phenotype in both sexes. A test cross of an F₁ male with the female parent produced 45% wild-type flies, 45% black, apterous flies, 5% flies with a black body and normal wings, and 5% apterous flies with a normal colored body. a. The two genes are autosomal b. Normal wings is dominant c. The two genes are on the same chromosome

Two genes can be syntenic and unlinked.

Which of the following statements about genetic and physical maps are true? Please select all that apply.

Match the missing words in the following phrase. Genomes in [A] could be mapped even though, unlike [B], they do not undergo meiotic [C]. Genes can be transferred between bacteria by [D] and bacterial genomes can be mapped according to [E]. Currently, bacterial genomes are almost always mapped by assessing the [F].

If recombination rate is high, then a particular combination of alleles is likely to be transferred to the next generation intact.

Which of the following are necessary characteristics of balancer chromosomes? Please select all that apply.

An experiment was conducted with Drosophila flies carrying recessive white-eye and yellow-body alleles. The white and yellow genes are on the X-chromosome. The parental (P₀) individuals were homozygous white-eye, normal body female and red-eye, yellow-body male. F₁ females had a wild-type phenotype and F₁ males had normal bodies and white eyes. F₁ individuals were then mated. What phenotypes are expected in the F₂ generation? Please select all that apply.

Ascomycete fungi are valuable models for studying recombination. Which of the following are advantages of these systems? Please select all that apply.

What does 10 centiMorgans (cM) represent?

Physical (top) and genetic (bottom) maps are shown for C. elegans chromosome I Physical and genetic maps can be used to determine the physical length of a map unit. Put the following intervals in C. elegans chromosome I in ascending order, from shortest physical length per map unit to longest (i.e., A = shortest, C = longest).

When genes are on the same chromosome, the alleles on one of the two homologous chromosomes are considered to be in trans.

Syntenic blocks are sections of chromosomes that have remained largely intact during evolution. For example, human chromosome 4 corresponds to syntenic blocks on mouse chromosomes 3, 5, and 8. Which of the following statements about synteny are true? Please select all that apply.

What are cytological maps used for?

Which structure that forms during meiosis leads directly to the formation of recombinant chromosomes?

Alleles for hairy body, curled wings, and glass eyes are on the same Drosophila chromosome. There are 23.5 map units between hairy and curled and 13 map units between curled and glass. One percent of offspring from a test cross had double crossovers. Was crossover interference observed?

Fill in the blank. In a cross between parents with the genotypes A/a;B/b and a/a;b/b, where the A and B loci are unlinked, __% of the offspring will have a phenotype that differs from the phenotype of both parents.