Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

4. Genetic Mapping and Linkage

Mapping Overview

Genetics

4. Genetic Mapping and Linkage

Mapping Overview

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2:16 minutes

Problem 1a

Textbook Question

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?

Verified step by step guidance

Understand the concept of recombination frequency: Recombination frequency refers to the percentage of offspring that exhibit new combinations of traits due to crossing over during meiosis. This frequency is used as a measure of the physical distance between two genes on a chromosome.

Review the experimental setup: Early experiments, such as those conducted by Thomas Hunt Morgan and his colleagues using Drosophila melanogaster (fruit flies), involved crossing individuals with known genetic markers and analyzing the offspring for recombination events.

Analyze the relationship between recombination frequency and gene distance: Researchers observed that genes located farther apart on the same chromosome exhibited higher recombination frequencies, while genes closer together showed lower frequencies. This suggested that crossing over is more likely to occur between genes that are physically separated by a greater distance.

Understand the use of genetic mapping: Geneticists used recombination frequencies to construct genetic maps, where the distance between genes is expressed in map units (centimorgans, cM). One map unit corresponds to a 1% recombination frequency.

Consider the reasoning behind the conclusion: The experimental data supported the hypothesis that recombination frequency is proportional to the physical distance between genes. This conclusion was validated by comparing genetic maps with physical maps derived from DNA sequencing, confirming the correlation between recombination frequency and gene distance.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Recombination Frequency

Recombination frequency refers to the proportion of offspring that exhibit a combination of traits different from those of their parents due to crossing over during meiosis. This frequency is used as a measure of genetic linkage, with higher recombination frequencies indicating that genes are located further apart on a chromosome, while lower frequencies suggest closer proximity.

Linkage and Genetic Mapping

Linkage describes the tendency of genes located close to each other on a chromosome to be inherited together. Genetic mapping utilizes recombination frequencies to create a map of gene locations on chromosomes, allowing researchers to estimate distances between genes based on how often they recombine during gamete formation.

Experimental Methods in Genetics

Experimental methods in genetics, such as test crosses and the use of model organisms, are essential for determining gene linkage and recombination frequencies. By analyzing the offspring of specific crosses, scientists can observe the inheritance patterns and calculate recombination frequencies, leading to insights about gene distances on chromosomes.

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Related Practice

Textbook Question

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?

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Textbook Question

How do we know that sister chromatids undergo recombination during mitosis?

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Textbook Question

How do we know that crossing over results from a physical exchange between chromatids?

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Textbook Question

How do we know that specific genes are linked on a single chromosome, in contrast to being located on separate chromosomes?

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Textbook Question

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.

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Textbook Question

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

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Textbook Question

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

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Textbook Question

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

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