Genetics Chapter 7: Linked Genes

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Questions and Answers

What happens when linkage between genes is broken down?

They remain linked.

Recombination occurs. (correct)

They are inherited together.

They follow Mendel's law of independent assortment.

What is the relationship between the frequency of recombination and the distance between genes?

The frequency of recombination is related to the distance between them.

What does the Principle of Segregation state?

Each diploid organism possesses two alleles at a locus that separate in meiosis, and that one allele passes into each gamete.

Define locus.

The position of a gene or mutation on a chromosome. Signup and view all the answers

What does the Principle of Independent Assortment imply?

It states that the two alleles separate independently of alleles at other loci. Signup and view all the answers

Who proposed the chromosome theory of heredity?

Walter Sutton. Signup and view all the answers

What are linked genes?

Genes located close together on the same chromosome. Signup and view all the answers

What is a linkage group?

A group of genes that travel together in meiosis and end up in the same gamete. Signup and view all the answers

What is non-recombinant progeny?

Progeny that contain only the original combinations of alleles. Signup and view all the answers

What is the difference between linkage and crossing over?

Linkage keeps particular genes together, while crossing over mixes them up. Signup and view all the answers

Define recombinant gametes.

Gametes with new combinations of alleles. Signup and view all the answers

Explain recombination frequency.

It is the proportion of recombinant progeny produced in a cross, calculated as (#recombinants / total # progeny) * 100. Signup and view all the answers

What dominates with linked genes and some crossing over?

Parental (nonrecombinant) genes Signup and view all the answers

What is interchromosomal recombination?

Recombination that occurs among genes located on different chromosomes. Signup and view all the answers

Define intrachromosomal recombination.

Recombination that takes place among genes located on the same chromosome. Signup and view all the answers

What is the coupling (cis) configuration?

An arrangement of linked genes where the wild-type alleles of two or more genes are on one chromosome. Signup and view all the answers

Describe the repulsion (trans) configuration.

An arrangement where each homologous pair of chromosomes contains one wild-type (dominant) allele and one mutant (recessive) allele. Signup and view all the answers

The arrangement of linked genes on a chromosome affects the results of a testcross.

True Signup and view all the answers

What is a genetic map?

A map of the relative distances between genetic loci, markers, or other chromosome regions. Signup and view all the answers

What are physical maps?

Maps of physical distances between loci or other chromosome segments measured in base pairs. Signup and view all the answers

What are map units?

Units of measure for distances on a genetic map, also known as centiMorgans. Signup and view all the answers

What is a centiMorgan?

A.k.a. a map unit. Signup and view all the answers

What can be said about genes that exhibit 50% recombination?

They are part of different linkage groups. Signup and view all the answers

What is a double crossover?

It arises when two separate crossover events take place between two loci. Signup and view all the answers

Study Notes

Linkage and Recombination

Linked genes do not assort independently and are inherited together due to their proximity on the same chromosome.
Recombination frequency, influenced by gene distance, helps predict inheritance patterns between linked genes.

Principles of Genetics

Principle of Segregation: Each diploid organism has two alleles for a locus that separate during meiosis; one allele goes to each gamete.
Principle of Independent Assortment: Alleles at different loci segregate independently during gamete formation.

Key Concepts in Linkage

Locus refers to the specific position of a gene or mutation on a chromosome.
Linked genes are situated close on the same chromosome, while linkage groups refer to sets of genes that travel together during meiosis.

Types of Progeny

Non-recombinant progeny (parentals) consist of original allele combinations.
Recombinant gametes have new combinations of alleles due to crossing over.

Genetic Testing

A testcross involving linked genes results in two progeny types reflecting the P generation traits, unlike independent assortment, which yields a 1:1:1:1 ratio of progeny types.
Chi-square tests can determine gene linkage.

Recombination Dynamics

Recombination frequency is calculated as (#recombinants/ total # progeny) x 100, indicating the extent of genetic mixing.
Interchromosomal recombination occurs between genes on different chromosomes, whereas intrachromosomal recombination happens among genes on the same chromosome.

Gene Configuration

Coupling (cis) configuration places wild-type alleles on one chromosome and mutant alleles on the homologous chromosome.
Repulsion (trans) configuration has each chromosome carry one wild-type and one mutant allele.

Mapping Genetics

Genetic maps illustrate the relative distances between genetic loci based on recombination rates, expressed in map units or centiMorgans.
Physical maps depict actual distances, measured in base pairs.

Two-Point Testcross Considerations

Distinguishing genes on different chromosomes from those far apart on the same chromosome can be challenging when recombination is at 50%.
Testcrosses for distantly located genes can underestimate their physical distance due to unobserved double crossovers.

Double Crossovers

Double crossover events involve two separate crossover occurrences between two loci, complicating genetic predictions and inheritance patterns.

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Description

Explore the concepts of linked genes and their inheritance patterns in this flashcard quiz. Learn how recombination affects gene linkage and the principle of segregation. Test your understanding of genetic linkage and the distance-dependent frequency of recombination.