a) What is the diffference between physical and genetic maps ofchromosomes and how are genetic maps constructed?
b) What does genetic distance mean?
c) Define chiasma(ta), recombination frequency, crossover rate,and double crossover.
d) Draw one figure supporting your answer. You are required toexplain and show the difference between crossover rate andrecombination frequency. Explain the units of genetic distance.
a) What is the diffference between physical and genetic maps ofchromosomes and how are genetic maps constructed?
b) What does genetic distance mean?
c) Define chiasma(ta), recombination frequency, crossover rate,and double crossover.
d) Draw one figure supporting your answer. You are required toexplain and show the difference between crossover rate andrecombination frequency. Explain the units of genetic distance.
Related textbook solutions
Related questions
Which of these statements is incorrect?
Syntenic genes are located on the same chromosome. |
Independent assortment results in recombinant chromosomes. |
You can reliably predict the relative genetic distance fromgenesâ physical distance on a chromosome. |
Linked genes are always syntenic. |
What is the relative genetic distance between two linked genesif the recombination frequency is 0.49?
0.49 cM |
4.9 cM |
49 cM |
490 cM |
What statement best explains the distortion in Mendelian ratiosobserved by Bateson & Punnett in 1905? (Reminder: they found anoverrepresentation of F2 offspring showing both dominant orrecessive phenotypes, and an underrepresentation of offspringdisplaying one dominant and one recessive phenotype)
| Human error: they should have been more careful about theirexperimental setup. |
| Gene linkage: Genes for flower color and pollen shape arephysically close on the same chromosome, leading to a breakdown inthe independent assortment of the alleles for these traits. |
| Chromosome crossover: Homologous recombination of twochromatids during meiosis caused the alleles to shuffle, resultingin a breakdown of the independent assortment of the alleles forthose genes. |
Random variation: No two situations are alike. In finitepopulations, you are going to get some variation across a mean. |
When determining the relative genetic distance between twogenes, why is dihybrid back-cross preferable over traditionaldihybrid cross?
| 9:3:3:1 phenotypic ratio is easier to work with than 1:1:1:1ratio. |
| Genotypes of the offspring can be determined based on theirphenotype. |
If the genes are independently assorted, the dihybrid back-crosswould result in only 2 genotypes in the F1 generation. |
B and C |
Why do we map genes?
| To understand how genes interact with each other |
| Comparative genomics analysis |
| To determine the genotype of an organism |
| All of the above |
You are a plant geneticist at the Tomato Genetics Resource Center at the University of California-Davis. You are studying three genes, which you know are on chromosome 3 of the tomato: R, S, and F.
Each gene has two alleles:
R causes red flesh; r causes yellow flesh.
S causes smooth skin; s causes fuzzy skin.
F causes round shape; f causes oblate shape.
You mate a tomato plant with red flesh, smooth skin, and oblate shape with a tomato with yellow flesh, fuzzy skin, and round shape. All of the F1 offspring have red flesh, smooth skin, and round shape. You conduct a test cross and mate F1 plants with plants possessing the recessive traits (yellow flesh, fuzzy skin, and oblate shape).
You count and classify the following offspring of the test cross:
| red smooth oblate | 371 |
| yellow fuzzy round | 370 |
| red fuzzy oblate | 68 |
| yellow smooth round | 58 |
| red fuzzy round | 34 |
| yellow smooth oblate | 40 |
| yellow fuzzy oblate | 10 |
| red smooth round | 6 |
Using the data listed above, construct a gene map between the genes R, S, and F. Calculate map unit values between all genes, and draw a diagram of the relationship between the genes.
1.) What is the distance between R and F in map units?
2.) Explain why, in general, the map distance between the two most distant genes is less than the sum of the distances between the closer pairs of genes.
3.) According to your map, which classes correspond to double-crossover events?
4.) If you have not so already, calculate the corrected map distance between the two most distant genes.
5.) Calculate the predicted number of double-crossover events. How does this compare to the observed number?
