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?
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What is recombination?
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What happens during crossing over?
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Recombination leads to ______ ______.
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What is independent assortment?
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Crossing over events can reassort _____ _______.
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What is the ultimate outcome of recombination via crossing over events?
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Genetic linkage mapping plots the positions of what?
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What does genetic linkage mapping allow us to infer?
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Who discovered a strain of corn that was heterozygous for a mutated chromosome 9?
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Mutated Chromosome 9 has a _______.
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In 1931, they visualized __________ __________.
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What is the role of a dihybrid double heterozygote in genetic linkage?
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What should you remember about genetic linkage in eukaryotes?
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Crossing over is more likely to occur between closely linked genes than those farther apart.
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Genetic linkage can be recognized by what?
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If genes are linked, parental allele combinations will be observed at a lower frequency than expected.
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Incomplete genetic linkage is less common than complete linkage.
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What is complete linkage?
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The two parental types are approximately equal in frequency when genes are fully linked.
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What does recombination frequency reflect?
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Linked genes with higher recombination frequencies are more ____ from one another than genes with lower frequencies.
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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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Description
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.
