Linkage Part 2 (easy)

Questions and Answers

What was the main objective of Harriet Creighton, Barbara McClintock, and Curt Stern's experiments?

To analyze the tetrad formation in ascomycetes

To map the genetic linkage in haploids

To provide evidence for genetic recombination through crossing over (correct)

To study the process of mitosis

What is the term used to describe the determination of the linear order and distance of separation of linked genes along the same chromosome?

Meiotic recombination

Linkage mapping

Genetic mapping (correct)

Tetrad analysis

What is the site where a gene is found within a particular chromosome?

Chromosomal segment

Gene cluster

Genetic hotspot

Locus (correct)

What was Curt Stern's experiment designed to show?

The correlation between crossing over and recombination Signup and view all the answers

What is the term used to describe the physical exchange of segments between homologous chromosomes?

Crossing over Signup and view all the answers

What is the purpose of generating a genetic linkage map?

To determine the linear order and distance of separation of linked genes Signup and view all the answers

What is the term used to describe the study of the inheritance of recombinant offspring?

Linkage analysis Signup and view all the answers

What is the advantage of using Drosophila melanogaster for genetic mapping?

They have a short generation time Signup and view all the answers

What is the map distance between the body color and eye color genes?

12.3 map units Signup and view all the answers

What is the correct order of the genes based on the map distance calculation?

b − pr − vg Signup and view all the answers

What is the formula to calculate the map distance between two linked genes?

Map distance = (NPD + (1/2)(T)) / Total number of asci Signup and view all the answers

What is the purpose of the product rule in predicting the likelihood of a double crossover?

To predict the likelihood of a double crossover from individual probabilities Signup and view all the answers

What is the significance of non-parental ditypes (NPD) in tetrad analysis?

NPD can be produced from a double crossover Signup and view all the answers

What is the expected number of double crossover offspring in a total of 1,005 offspring?

7.5 Signup and view all the answers

What is the phenomenon that results in a lower-than-expected number of double crossover offspring?

Positive interference Signup and view all the answers

What is the relationship between single crossovers (SCO) and tetratypes (T) in tetrad analysis?

T can result from SCO or DCO Signup and view all the answers

How are double crossovers (DCO) measured in tetrad analysis?

DCO = 4NPD Signup and view all the answers

What is the coefficient of coincidence (C) in this case?

0.4 Signup and view all the answers

What is the purpose of tetrad analysis in genetic mapping?

To identify the genetic distance between two linked genes Signup and view all the answers

What is the result of mitotic recombination during an early stage of embryonic development?

A patch of tissue with characteristics different from the rest of the organism Signup and view all the answers

What is the name of the phenomenon observed by Curt Stern in Drosophila?

Twin spot Signup and view all the answers

What is the purpose of mitotic recombination?

Not a biological purpose, it is a rare event Signup and view all the answers

What is the limitation of using the formula Map distance = (NPD + (1/2)(T)) / Total number of asci?

It does not account for double crossovers Signup and view all the answers

During which stage of cell division does mitotic recombination occur?

Mitosis Signup and view all the answers

What is the significance of tetratype (T) in tetrad analysis?

T can result from a single crossover or a double crossover Signup and view all the answers

Study Notes

Inheritance of Recombinant Offspring

Harriet Creighton, Barbara McClintock, and Curt Stern performed crosses involving two linked genes to obtain direct evidence that genetic recombination is due to crossing over.
They aimed to see if there was a correlation between the occurrence of recombinant offspring and microscopically observable exchanges in segments of homologous chromosomes.

Genetic Mapping

Genetic mapping (also known as gene mapping or chromosome mapping) is performed to determine the linear order and distance of separation of linked genes along the same chromosome.
Each gene has its own unique locus, the site where the gene is found within a particular chromosome.

Simplified Genetic Linkage Map of Drosophila melanogaster

The map distance between body color and eye color is 12.3 map units.

Calculating Map Distance

The map distance between two genes can be calculated using the formula: Map distance = (Recombinant Offspring / Total) × 100.
The map distance is used to construct a genetic linkage map, which shows the relative positions of genes along a chromosome.

Interference

Interference occurs when the frequency of double crossovers is less than expected based on the product rule.
Positive interference means that the occurrence of one crossover reduces the probability of another crossover nearby.
Interference is calculated as I = 1 − C, where C is the coefficient of coincidence.

Mitotic Recombination

Mitotic recombination occurs when crossing over happens during mitosis, resulting in a new combination of alleles.
This process can produce a patch of tissue with characteristics different from the rest of the organism.
Curt Stern proposed that unusual patches on the bodies of certain Drosophila strains were due to mitotic recombination.

Mitotic Crossing Over in Drosophila

Curt Stern worked with strains carrying X-linked genes affecting body color and bristle morphology.
He observed twin spots, which are adjacent regions with different characteristics, and proposed that they were due to a single mitotic recombination within one cell during embryonic development.

Relationship between Crossing Over and PD, T, and NPD for Two Linked Genes

The relationship between crossing over and PD, T, and NPD can be used to calculate the map distance between two linked genes.
PD (Parental Ditype), T (Tetratype), and NPD (Non-Parental Ditype) are types of asci that can be used to determine the map distance.

Data from a Tetrad Analysis

Data from a tetrad analysis can be used to calculate the map distance between two linked genes.
The map distance is calculated as (NPD + (1/2) (T)) / Total number of asci × 100.
A more precise way to calculate map distance is: (Single crossover tetrads + (2) (Double cross over tetrads)) / Total number of asci × 0.5 × 100.

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Description

This quiz covers the experiment by Harriet Creighton, Barbara McClintock, and Curt Stern on linked genes to prove genetic recombination due to crossing over. It discusses the correlation between recombinant offspring and microscopically observable crossover events.