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 1c

Textbook Question

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

Verified step by step guidance

Understand the concept of crossing over: Crossing over is the process during meiosis where homologous chromosomes exchange genetic material between non-sister chromatids. This exchange increases genetic diversity in gametes.

Review experimental evidence: The physical exchange of chromatids was demonstrated through experiments using organisms like Drosophila (fruit flies). Researchers observed that recombination frequencies correlated with physical distances between genes on chromosomes.

Examine cytological observations: During meiosis, under a microscope, chiasmata (visible points of contact between homologous chromosomes) can be observed. These chiasmata are physical evidence of crossing over, where chromatids exchange segments.

Consider genetic mapping: Geneticists use recombination frequencies to create linkage maps. These maps show that genes closer together on a chromosome have lower recombination frequencies, supporting the idea of physical exchange during crossing over.

Analyze molecular evidence: Modern techniques, such as DNA sequencing, confirm that recombination involves the breaking and rejoining of DNA strands. Enzymes like recombinases facilitate this process, providing direct molecular evidence of physical exchange between chromatids.

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Key Concepts

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

Crossing Over

Crossing over is a genetic process that occurs during meiosis, where homologous chromosomes exchange segments of genetic material. This physical exchange between chromatids leads to genetic recombination, increasing genetic diversity in offspring. The phenomenon is crucial for understanding inheritance patterns and the genetic variation observed in populations.

Chromatids

Chromatids are the two identical halves of a replicated chromosome, joined together at a region called the centromere. During meiosis, these chromatids can undergo crossing over, which allows for the exchange of genetic information. Understanding the structure and behavior of chromatids is essential for grasping how genetic traits are inherited and how genetic diversity arises.

Chromosomal Mapping

Chromosomal mapping is a technique used to determine the relative positions of genes on a chromosome. It involves analyzing the frequency of recombination events, such as crossing over, to infer the distances between genes. This mapping is fundamental for understanding genetic linkage and the inheritance of traits, as it provides insights into how genes are organized and interact within the genome.

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Related Practice

Multiple Choice

Which of the following steps is essential when using a three-factor cross to map the order and distances between genes on a chromosome?

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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?

365

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Textbook Question

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

362

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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?

408

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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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