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Chapter 5: Problem 5

Why does more crossing over occur between two distantly linked genes than between two genes that are very close together on the same chromosome?

Short Answer

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Answer: More crossing over occurs between distantly linked genes because there is a greater probability for the homologous chromosomes to align at various points and exchange genetic material. As the distance between two genes increases, there are more opportunities for chromosomal exchange without affecting one or both genes, leading to more frequent crossing over events. This process helps to ensure genetic diversity in the offspring.

Step by step solution

01

Introduction to Chromosomes and Genes

Chromosomes are long strands of DNA that contain many genes. Genes are segments of DNA that code for a specific protein or trait. During the formation of gametes (sperm and egg), chromosomes are arranged in homologous pairs, meaning each chromosome in a pair carries the same genes but may have different variations of those genes (alleles).
02

Meiosis and Crossing Over

Meiosis is the process of cell division that produces gametes with half the number of chromosomes of the parent cell. During the prophase I of meiosis, homologous chromosomes pair up, forming a structure called a bivalent or a tetrad. It is during this stage that crossing over occurs. Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes, leading to the recombination of genetic information.
03

Recombination Frequency and Genetic Distance

The frequency of recombination, or crossing over, is related to the distance between two genes on a chromosome. The greater the distance between two genes, the more likely it is for a crossover event to occur between them. This is because the homologous chromosomes have a higher probability of aligning and exchanging DNA at different points when the genes are far apart.
04

Why More Crossing Over Occurs Between Distantly Linked Genes

More crossing over occurs between two distantly linked genes because there is a greater probability for the homologous chromosomes to align at various points and exchange genetic material. When two genes are close together, there aren't many points where chromosomal exchange can occur without affecting one or both genes. As a result, crossing over events are less frequent between closely linked genes as compared to distantly linked genes. This is an essential process to ensure genetic diversity in the offspring.

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Most popular questions from this chapter

The genes dumpy\((d p),\) clot \((c l),\) and apterous \((a p)\) are linked on chromosome II of Drosophila. In a series of two-point mapping crosses, the following genetic distances were determined. What is the sequence of the three genes?

Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body. The \(\mathrm{F}_{1}\) Lobe females were then backcrossed with homozygous smooth abdomen, straw body males, and the following phenotypes were observed: (a) Give the gene order and map units between these three loci. (b) What is the coefficient of coincidence?

What two essential criteria must be met in order to execute a successful mapping cross?

What possible conclusions can be drawn from the observations that in male Drosophila, no crossing over occurs, and that during meiosis, synaptonemal complexes are not seen in males but are observed in females where crossing over occurs?

Three loci, mitochondrial malate dehydrogenase that forms \(a\) and \(b(M D H a, M D H b),\) glucouronidase that forms 1 and 2 \((G U S 1, G U S 2),\) and a histone gene that forms \(+\) and \(-\left(H^{+},\right.\) \(\left.H^{-}\right),\) are located on chromosome \(\\# 7\) in humans. Assume that the \(M D H\) locus is at position \(35, G U S\) at position \(45,\) and \(H\) at position \(75 .\) A female whose mother was homozygous for \(M D H a, G U S 2,\) and \(H^{+}\) and whose father was homozygous for \(M D H b, G U S 1,\) and \(H^{-}\) produces a sample of 1000 egg cells. Give the genotypes and expected numbers of the various types of cells she would produce. Assume no chromosomal interference.
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