Linkage Part 1 (Medium)

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Questions and Answers

What is the result of crossing over during meiosis?

Haploid cells are formed

Recombinant genotypes are produced (correct)

Linked genes always segregate together

Homologous chromosomes separate

What is the term for haploid cells containing a combination of alleles not found in the original chromosomes?

Mutant cells

Hybrid cells

Parental cells

Recombinant cells (correct)

What is the main reason for the formation of recombinant offspring?

Crossing over during meiosis (correct)

Mutation during DNA replication

Gene expression during development

Independent assortment of chromosomes

What did Thomas Hunt Morgan's experiments involve?

Investigating the X-linked pattern of inheritance in Drosophila Signup and view all the answers

What is the term used to describe two or more genes located on the same chromosome?

Synteny Signup and view all the answers

What is the explanation for the high proportion of combinations of traits found in the parental generation in Morgan's three-factor cross?

All three genes are located on the X chromosome Signup and view all the answers

What is the phenomenon where genes close together on a chromosome tend to be transmitted as a unit?

Genetic Linkage Signup and view all the answers

What is the term for the physical association of replicated sister chromatids from homologous chromosomes?

Bivalent Signup and view all the answers

Why does crossing over allow genes far apart on the same chromosome to independently assort from each other?

Because it allows for recombination Signup and view all the answers

What type of cross would be used to study linkage between three genes?

Three-factor cross Signup and view all the answers

What is the result of no crossing over during meiosis?

Linked genes always segregate together Signup and view all the answers

During which stage of meiosis does crossing over occur?

Prophase I Signup and view all the answers

What did Bateson and Punnett observe when they crossed two traits, flower color and pollen shape?

A deviation from the expected 9:3:3:1 phenotypic ratio Signup and view all the answers

What is the number of linkage groups in humans?

24 Signup and view all the answers

What is the reason why genes close together on a chromosome do not always assort independently?

Because of genetic linkage Signup and view all the answers

What is the term used to describe the chromosomes that contain a group of linked genes?

Linkage groups Signup and view all the answers

What was Janssens' contribution to the understanding of crossing over?

He observed chiasmata and proposed that crossing over involves a physical exchange between homologous chromosomes Signup and view all the answers

Why did Morgan assume that crossing over did not occur between the X and Y chromosomes?

Because the three genes were not found on the Y chromosome Signup and view all the answers

What is the result of crossing over between homologous X chromosomes in females?

The creation of new combinations of alleles Signup and view all the answers

What is the relationship between the distance between two genes and the likelihood of crossing over?

The likelihood of crossing over increases as the distance between two genes increases Signup and view all the answers

What is the result of genetic linkage?

The tendency of alleles to be inherited together Signup and view all the answers

Why did Morgan propose that the genes for body color, eye color, and wing length are located on the X chromosome?

Because they are sex-linked traits Signup and view all the answers

Study Notes

Meiosis and Crossing Over

Crossing over occurs during Prophase of Meiosis I, where non-sister chromatids of homologous chromosomes exchange DNA segments.
Replicated sister chromatids (homologues) associate as bivalents.
Crossing over can produce recombinant genotypes.

Recombinant Cells and Offspring

Haploid cells containing a combination of alleles not found in the original chromosomes are called non-parental or recombinant cells.
Recombinant offspring are produced by the exchange of DNA between two homologous chromosomes during meiosis in one or both parents.
Recombinant offspring have a novel combination of genetic material due to a crossover event during gamete formation in (at least) one of their parents.

Morgan's Experiments

Thomas Hunt Morgan's experiments provided the first direct evidence of linkage in Drosophila.
He investigated three traits: body color, eye color, and wing length, which showed a non-parental combination of traits.
Morgan observed a higher proportion of trait combinations found in the parental generation, suggesting that the genes are located on the X chromosome and tend to be transmitted together as a unit.

Linkage and Synteny

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

Bateson and Punnett's Cross

Bateson and Punnett's cross involving two traits (flower color and pollen shape) did not yield the expected 9:3:3:1 phenotypic ratio.
This suggests that independent assortment does not always occur.

Altering Linkage

Janssens proposed that crossing over involves a physical exchange between homologous chromosomes, which Morgan realized was consistent with his data.
Morgan assumed crossing over did not occur between the X and Y chromosomes.
The three genes studied by Morgan were not found on the Y chromosome.

Morgan's Hypotheses

Morgan hypothesized that the genes for body color, eye color, and wing length are located on the X-chromosome.
He proposed that alleles will tend to be inherited together due to crossing over.
The likelihood of crossing over depends on the distance between the two genes, with crossing over more likely to occur between genes that are far apart.

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Description

Explore the process of meiosis, including crossing over during prophase, and its impact on genetic recombination, producing recombinant cells and offspring.