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?

<p>To study independent assortment of two traits (C)</p> Signup and view all the answers

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

<p>Most combinations were parental (C)</p> Signup and view all the answers

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

<p>They independently assort from each other (C)</p> Signup and view all the answers

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

<p>Genetic linkage (B)</p> Signup and view all the answers

What is the purpose of a dihybrid cross?

<p>To study the inheritance of two traits (C)</p> Signup and view all the answers

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

<p>A ratio that did not match the expected 9:3:3:1 phenotypic ratio (C)</p> Signup and view all the answers

What is the number of linkage groups in humans?

<p>22 autosomal linkage groups, 1 X chromosome linkage group, 1 Y chromosome linkage group (C)</p> Signup and view all the answers

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

<p>It increases the frequency of recombinant offspring (B)</p> Signup and view all the answers

What is the result of genetic linkage on inheritance patterns?

<p>It decreases the frequency of independent assortment (B)</p> Signup and view all the answers

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

<p>Crossing over (A)</p> Signup and view all the answers

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

<p>Because the genes were physically linked on the same chromosome (A)</p> Signup and view all the answers

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

<p>Chi square analysis (D)</p> 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?

<p>Recombinant cells (B)</p> Signup and view all the answers

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

<p>To determine if the genes are linked or assorting independently (A)</p> Signup and view all the answers

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

<p>Because it allows us to calculate expected values (A)</p> Signup and view all the answers

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

<p>The pattern of inheritance of the traits (C)</p> Signup and view all the answers

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

<p>To reject the hypothesis of independent assortment (A)</p> Signup and view all the answers

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

<p>Dihybrid cross (C)</p> Signup and view all the answers

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

<p>To compare with observed values and determine if they are significantly different (A)</p> Signup and view all the answers

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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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