Gene Mapping and Genetic Distance

Questions and Answers

What is the distance between two gene loci if 100% recombination frequency is seen?

1 Morgan Unit (correct)

1 centimorgan (cM)

100 Map Units

1 Map Unit

If the distance between two gene loci is 16 cM, what percentage of crossover gametes can be expected?

16% (correct)

32%

25%

What is the purpose of a three-point test cross?

To calculate the crossing over frequency

To detect linkage between genes

To determine the gene order

To avoid double crossover between genes less than 5 cM apart (correct)

If an F1 dihybrid produces 20% crossover gametes, what is the distance between the two gene loci?

20 cM Signup and view all the answers

What is the total length of a genetic map if the mean number of chiasmata is 3?

150 cM Signup and view all the answers

In a dihybrid test cross, what percentage of F2 progeny is formed by crossing over?

26% Signup and view all the answers

What unit is preferred by most geneticists to measure the distance between genes?

Map Unit Signup and view all the answers

If the distance between two gene loci is 50 cM, how many chiasmata are expected to occur between them?

1 Signup and view all the answers

What is the purpose of using a marker gene in a trihybrid test cross?

To determine the linear distance between two genes Signup and view all the answers

What is the total crossover frequency between genes A and C?

20% + 10% = 30% Signup and view all the answers

What is the map unit distance between genes A and C?

30 Map Units/cM Signup and view all the answers

How can the gene order be determined in a trihybrid test cross?

By comparing the crossover frequencies between genes Signup and view all the answers

What is the chiasma frequency between genes A and B?

18% Signup and view all the answers

In a trihybrid test cross, what is the purpose of the parental type?

To determine the crossover frequency between genes Signup and view all the answers

What is the linkage mapping used for?

To construct a genetic map of the organism Signup and view all the answers

What is the correct order of genes A, B, and C, given the following distances: A-B = 12 cM, B-C = 7 cM, A-C = 5 cM?

A-C-B Signup and view all the answers

What was the primary objective of the Human Genome Project?

To determine the complete genome sequence of humans Signup and view all the answers

What is the relationship between the rate of crossing-over of genes and the distances between them?

The rate of crossing-over decreases with an increase in distance between genes Signup and view all the answers

Why is genetic mapping important in breeding programs?

To select desirable traits in breeding programs Signup and view all the answers

What is the significance of genetic mapping in the study of genetic diseases?

It helps to understand the causes and preventive measures of genetic diseases Signup and view all the answers

Who are considered to be the pioneers of genetic mapping?

Alfred Sturtevant and Thomas Hunt Morgan Signup and view all the answers

What is the basis of constructing a linkage map?

The frequency of crossing-over between genes Signup and view all the answers

What is the significance of genetic mapping in biotechnological practices?

It is used in gene cloning, genetic modification, etc. Signup and view all the answers

What is the name of the project that aimed to determine the complete genome sequence of humans?

The Human Genome Project Signup and view all the answers

Study Notes

Gene Mapping

Customary units of light microscopy cannot be used to measure distance between genes because they are too small.
An arbitrary unit called the Map Unit (also known as Centimorgan, cM) is used to measure genetic distance.
1 Map Unit is equal to 100 Morgan Units, and it is the distance between two genes that have a 1% recombination frequency.

Measuring Crossing Over Frequency

Two-Point/Dihybrid Test Cross is used to calculate the percentage of crossing over in an F1 dihybrid by crossing it with a double recessive parent.
The results of the F2 generation are used to calculate the percentage of crossing over, which is then used to determine the distance between two gene loci.
For example, if the percentage of crossing over is 26%, the distance between the gene loci is 26 cM.

Three-Point/Trihybrid Test Cross

Three-Point/Trihybrid Test Cross is used to determine the distance between two genes when they are less than 5 cM apart.
A marker gene is used to ascertain the linear distance between two genes.
The results of the F2 generation are used to calculate the distance between the genes.

Determining Gene Order

Gene order can be determined by testing the distance between genes.
The order of genes can be determined by finding the shortest distance between them.

Genetic and Cytological Mapping of Chromosomes

Genetic mapping provides a diagrammatic representation of relative distances between linked genes of a chromosome.
American geneticists Alfred Sturtevant and Thomas Hunt Morgan are considered pioneers of genetic mapping.
Genetic mapping is significant in studying genetic diseases, selecting desirable traits in breeding programs, studying phylogeny, and biotechnological practices.

Construction of a Linkage Map

The rate of crossing-over of genes and the distances between them are related, with shorter distances resulting in a greater chance of crossing-over.
Genes are present in a linear form in chromosomes, and the distance between them can be determined by measuring the crossing-over frequency.

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Description

Learn about gene mapping, measuring genetic distance, and crossing over frequency. Understand the concept of Map Units and its relation to recombination frequency.