Linked Genes Flashcards
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Questions and Answers

Genes located on the same chromosome are called ___ ____.

syntenic genes.

What are linked genes?

Syntenic genes that are so close together that their alleles cannot assort independently.

What does the Linked Gene Offspring Rule state?

Their offspring do NOT fall out in expected 9:3:3:1 ratio in a cross of double heterozygotes.

What can genetic linkage be quantified to do?

<p>Map the positions of genes on chromosomes.</p> Signup and view all the answers

What is recombination?

<p>Sorting of alleles into new combinations.</p> Signup and view all the answers

What happens during crossing over?

<p>Physical exchange of pieces of chromosomes between non-sister chromatids.</p> Signup and view all the answers

Recombination leads to ______ ______.

<p>Genetic variation.</p> Signup and view all the answers

What is independent assortment?

<p>Random distribution of chromosomes into gametes.</p> Signup and view all the answers

Crossing over events can reassort _____ _______.

<p>linked alleles.</p> Signup and view all the answers

What is the ultimate outcome of recombination via crossing over events?

<p>In meiosis II, genes that are normally linked can assort independently.</p> Signup and view all the answers

Genetic linkage mapping plots the positions of what?

<p>Genes on chromosomes.</p> Signup and view all the answers

What does genetic linkage mapping allow us to infer?

<p>Based on how often we get recombinants, we can infer the distance between two linked genes.</p> Signup and view all the answers

Who discovered a strain of corn that was heterozygous for a mutated chromosome 9?

<p>Harriet Creighton and Barbara McClintock.</p> Signup and view all the answers

Mutated Chromosome 9 has a _______.

<p>Translocation.</p> Signup and view all the answers

In 1931, they visualized __________ __________.

<p>Intrachromosomal recombination.</p> Signup and view all the answers

What is the role of a dihybrid double heterozygote in genetic linkage?

<p>A and B will undergo independent assortment and produce four different gamete combinations.</p> Signup and view all the answers

What should you remember about genetic linkage in eukaryotes?

<p>Linked genes are always syntenic and located near one another.</p> Signup and view all the answers

Crossing over is more likely to occur between closely linked genes than those farther apart.

<p>False</p> Signup and view all the answers

Genetic linkage can be recognized by what?

<p>Comparing observed frequencies of gametes or progeny phenotypes with those expected under independent assortment.</p> Signup and view all the answers

If genes are linked, parental allele combinations will be observed at a lower frequency than expected.

<p>False</p> Signup and view all the answers

Incomplete genetic linkage is less common than complete linkage.

<p>False</p> Signup and view all the answers

What is complete linkage?

<p>A mixture of parental and nonparental gametes are produced.</p> Signup and view all the answers

The two parental types are approximately equal in frequency when genes are fully linked.

<p>True</p> Signup and view all the answers

What does recombination frequency reflect?

<p>The physical distance between two genes.</p> Signup and view all the answers

Linked genes with higher recombination frequencies are more ____ from one another than genes with lower frequencies.

<p>distant.</p> Signup and view all the answers

Study Notes

Genetic Linkage and Syntenic Genes

  • Genes located on the same chromosome are referred to as syntenic genes.
  • Linked genes are syntenic genes positioned closely, preventing independent assortment of their alleles.

Linked Gene Offspring Rule

  • In offspring from double heterozygotes, ratios deviate from the expected 9:3:3:1 due to gene linkage.

Mapping and Recombination

  • Genetic linkage can be quantitatively analyzed to map gene positions on chromosomes.
  • Recombination involves sorting alleles into new combinations through physical exchanges during crossing over at Prophase I.

Genetic Variation

  • Recombination contributes to genetic variation among organisms.

Independent Assortment

  • Independent assortment refers to the random distribution of chromosomes into gametes at Anaphase.

Linked Alleles and Crossing Over

  • Crossing over can shuffle linked alleles but is less likely between genes that are closely linked.
  • Parental or non-recombinant cells display familiar allele combinations at high frequencies.

Outcomes of Recombination

  • Crossing over allows genes that are normally linked to assort independently during meiosis II, enhancing genetic diversity.

Genetic Linkage Mapping

  • Genetic linkage mapping identifies the positions of genes, allowing inference of distances between linked genes based on recombination frequency.

Historical Context and Discoveries

  • Harriet Creighton and Barbara McClintock discovered a heterozygous strain of corn with a translocated mutated chromosome 9.
  • They visualized intrachromosomal recombination through the distinct appearance of homologous chromosomes under a microscope.

Dihybrid Crosses

  • In dihybrid crosses involving unlinked genes, independent assortment yields four gamete combinations with equal frequency.
  • Linked genes produce more parental combinations than nonparental, skewing frequencies.

Key Concepts of Genetic Linkage

  • Linked genes are syntenic and situated near one another on chromosomes.
  • Genetic linkage typically results in parental allele combinations being more frequent than nonparental combinations.

Recognizing Genetic Linkage

  • Genetic linkage can be identified by comparing observed progeny phenotype frequencies to those expected under independent assortment.
  • If genes are linked, parental allele combinations appear more frequently than chance predictions.

Complete vs. Incomplete Linkage

  • Incomplete genetic linkage is more common than complete linkage.
  • Complete linkage results in equal frequencies of parental and recombinant types.

Recombination Frequency

  • Recombination frequency varies based on gene pairs' physical distance on chromosomes, forming a predictable mapping relationship.
  • Greater distances between genes yield higher recombination rates, while closer genes exhibit lower rates.

Implications of Recombination Frequency

  • Higher recombination frequencies indicate genes are more distantly located on the chromosome compared to those with lower frequencies.

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Test your knowledge of linked genes and their properties with these flashcards. Learn about syntenic genes, the concept of linkage, and the expected offspring ratios in genetic crosses. Perfect for students studying genetics or preparing for exams.

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