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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2:01 minutes

Problem 1b

Textbook Question

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

Verified step by step guidance

Understand the concept of genetic linkage: Genetic linkage occurs when genes are located close to each other on the same chromosome, causing them to be inherited together more often than expected by independent assortment. This is a key principle in determining whether genes are linked.

Examine recombination frequency: When genes are linked, the frequency of recombination between them is lower than 50%. Recombination frequency is calculated by analyzing the offspring of a genetic cross and determining the proportion of recombinant phenotypes. Use the formula:

Recombination Frequency = \frac{Number of Recombinants}{Total Number of Offspring}

Perform a test cross: A test cross involves crossing a heterozygous individual for the genes of interest with a homozygous recessive individual. Analyze the offspring phenotypes to determine if the genes are linked based on the observed recombination frequency.

Use a genetic map: Genetic mapping involves determining the relative positions of genes on a chromosome based on recombination frequencies. If genes are linked, their recombination frequency will be proportional to their physical distance on the chromosome. This can be expressed in map units (centimorgans, cM).

Compare to independent assortment: If genes are located on separate chromosomes, they will assort independently during meiosis, resulting in a recombination frequency of approximately 50%. This contrasts with linked genes, which show recombination frequencies less than 50%, confirming their location on the same chromosome.

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Key Concepts

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

Genetic Linkage

Genetic linkage refers to the tendency of genes located close to each other on the same chromosome to be inherited together during meiosis. This occurs because linked genes are less likely to be separated by recombination events. Understanding linkage is crucial for determining the relative positions of genes on chromosomes and for predicting inheritance patterns.

Chromosomal Mapping

Chromosomal mapping is a technique used to determine the location of genes on a chromosome. It involves analyzing the frequency of recombination between genes, which provides insights into their relative distances. The closer two genes are on a chromosome, the lower the recombination frequency, allowing researchers to create genetic maps that illustrate gene positions.

Recombination Frequency

Recombination frequency is the measure of how often two genes are separated during meiosis due to crossing over. It is expressed as a percentage and is used to infer the distance between genes on a chromosome. A lower recombination frequency indicates that genes are likely linked on the same chromosome, while a higher frequency suggests they may be located on different chromosomes.

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Related Practice

Multiple Choice

In the context of bacterial genetic mapping, what does it mean if the trp gene is said to be located at 26 minutes on the E. coli chromosome?

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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 was it established experimentally that the frequency of recombination (crossing over) between two genes is related to the distance between them along the chromosome?

631

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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.

659

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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.

547

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Textbook Question

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

648

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