Genetics Chapter 6: Linkage (easy)

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Questions and Answers

What does the term synteny refer to?

Genes that are not physically linked

Genes that are far apart on the same chromosome

Genes located on different chromosomes

Two or more genes located on the same chromosome (correct)

What is the result of crossing over during meiosis?

Linked genes segregate independently

Only maternal chromosomes are involved

Recombinant genotypes are produced (correct)

All alleles are lost

Why do genes close to one another on the same chromosome not follow Mendel's law of independent assortment?

Because they are far apart on the same chromosome

Because they are not genetically linked

Because they are located on different chromosomes

Because they are physically linked and tend to be transmitted as a unit (correct)

What is the purpose of a two-factor cross?

To study independent assortment of two traits Signup and view all the answers

In Morgan's three-factor cross, what did he observe about the combinations of traits?

Most combinations were parental Signup and view all the answers

What is the result of crossing over between genes that are far apart on the same chromosome?

They independently assort from each other Signup and view all the answers

What is the term for the process by which genes on the same chromosome are transmitted together?

Genetic linkage Signup and view all the answers

What is the purpose of a dihybrid cross?

To study the inheritance of two traits Signup and view all the answers

What did Bateson and Punnett observe in their dihybrid cross experiment?

A ratio that did not match the expected 9:3:3:1 phenotypic ratio Signup and view all the answers

What is the number of linkage groups in humans?

22 autosomal linkage groups, 1 X chromosome linkage group, 1 Y chromosome linkage group Signup and view all the answers

What is the result of crossing over on the frequency of recombinant offspring?

It increases the frequency of recombinant offspring Signup and view all the answers

What is the result of genetic linkage on inheritance patterns?

It decreases the frequency of independent assortment Signup and view all the answers

What is the term for the exchange of DNA between two homologous chromosomes during meiosis?

Crossing over Signup and view all the answers

Why did Bateson and Punnett's experiment not yield the expected 9:3:3:1 phenotypic ratio?

Because the genes were physically linked on the same chromosome Signup and view all the answers

What is the term for the probability of observing a certain combination of traits?

Chi square analysis Signup and view all the answers

What is the term for the offspring that have a combination of alleles not found in the original parents?

Recombinant cells Signup and view all the answers

What is the primary purpose of performing a chi square analysis in the context of a dihybrid cross?

To determine if the genes are linked or assorting independently Signup and view all the answers

Why is it important to propose a hypothesis of independent assortment in a chi square analysis?

Because it allows us to calculate expected values Signup and view all the answers

What is the primary difference between genetic linkage and independent assortment?

The pattern of inheritance of the traits Signup and view all the answers

What is the goal of rejecting the null hypothesis in a chi square analysis?

To reject the hypothesis of independent assortment Signup and view all the answers

What type of cross is being analyzed in a chi square analysis?

Dihybrid cross Signup and view all the answers

What is the purpose of calculating expected values in a chi square analysis?

To compare with observed values and determine if they are significantly different Signup and view all the answers

Study Notes

Introduction to Linkage

Each species has thousands to tens of thousands of genes, but only a few dozen chromosomes, which means each chromosome carries many hundred or even thousands of different genes.
The transmission of genes close to one another on the same chromosome violates Mendel's law of independent assortment.

Synteny and Genetic Linkage

Synteny refers to two or more genes located on the same chromosome and being physically linked.
Genetic Linkage is the phenomenon where genes close together on a chromosome tend to be transmitted as a unit, influencing inheritance patterns.
Chromosomes are called linkage groups, containing a group of linked genes.
The number of linkage groups is equivalent to the number of types of chromosomes in the species.

Bateson and Punnett's Experiment

Bateson and Punnett conducted a two-factor cross involving flower color and pollen shape, which did not yield the expected 9:3:3:1 phenotypic ratio.
The results indicated that the genes were not assorted independently, but rather were linked on the same chromosome.

Crossing Over and Linkage

Linkage is altered during meiosis due to crossing over, which occurs during Prophase I.
Crossing over involves the exchange of DNA segments between non-sister chromatids of homologous chromosomes.
Recombinant offspring are produced through crossing over, resulting in novel combinations of genetic material.

Morgan's Experiments

Thomas Hunt Morgan provided the first direct evidence of linkage through studies on X-linked traits in Drosophila.
Morgan's three-factor cross involving body color, eye color, and wing length showed a significant number of non-parental combinations, indicating linkage.
Morgan concluded that the genes were located on the X chromosome and tend to be transmitted together as a unit.

Chi Square Analysis

Chi Square Analysis is a statistical method used to determine if the outcome of a dihybrid cross is consistent with linkage or independent assortment.
The method involves proposing a hypothesis of independent assortment and calculating expected values.
The analysis allows for the rejection of the hypothesis of independent assortment in favor of a linkage hypothesis.

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Description

This quiz covers the concept of linkage in genetics, where genes close to each other on the same chromosome are transmitted together, violating Mendel's law of independent assortment.