Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 5: Problem 3

Describe the cytological observation that suggests that crossing over occurs during the first meiotic prophase.

Short Answer

Expert verified
Answer: The formation of chiasmata during the pachytene stage of the first meiotic prophase is a cytological observation that suggests crossing over has occurred. Chiasmata are visible X-shaped structures formed when homologous chromatids have physically exchanged segments of their genetic material, leading to genetic recombination.

Step by step solution

01

Understanding crossing over

Crossing over is a process where homologous chromosomes exchange genetic material during the formation of gametes. This occurs during the first meiotic prophase and results in genetic recombination, increasing the diversity of offspring.
02

Identifying the stages of the first meiotic prophase

The first meiotic prophase consists of five stages: leptotene, zygotene, pachytene, diplotene, and diakinesis. Crossing over occurs during the pachytene stage, but there are several cytological observations throughout these stages that suggest that crossing over has occurred.
03

Observations during the leptotene and zygotene stages

During the leptotene stage, the chromosomes begin to condense, making them visible under a microscope. In the zygotene stage, homologous chromosomes pair up and start to form structures called synaptonemal complexes. At this stage, they are closely aligned and are ready for genetic material exchange.
04

Cytological observations during pachytene stage

In the pachytene stage, crossing over takes place. The cytological observation that suggests crossing over has occurred is the formation of chiasmata, which are visible X-shaped structures formed when homologous chromatids have physically exchanged segments of their genetic material. This exchange leads to genetic recombination.
05

Observations during diplotene and diakinesis stages

During the diplotene stage, the chromosomes start to separate but remain attached at the chiasmata points. The chiasmata begin to move toward the ends of the chromosomes in a process called terminalization. In the final stage, diakinesis, the chromosomes continue to condense, and the chiasmata become more noticeable. By observing the formation of chiasmata and the progression of these structures throughout the first meiotic prophase, we can conclude that crossing over has occurred during this stage of meiosis.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

An organism of the genotype \(A a B b C c\) was testcrossed to a triply recessive organism (aabbcc). The genotypes of the progeny are presented in the following table. (a) If these three genes were all assorting independently, how many genotypic and phenotypic classes would result in the offspring, and in what proportion, assuming simple dominance and recessiveness in each gene pair? (b) Answer part (a) again, assuming the three genes are so tightly linked on a single chromosome that no crossover gametes were recovered in the sample of offspring. (c) What can you conclude from the actual data about the location of the three genes in relation to one another?

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.

Colored aleurone in the kernels of corn is due to the dominant allele \(R\). The recessive allele \(r,\) when homozygous, produces colorless aleurone. The plant color (not the kernel color) is controlled by another gene with two alleles, \(Y\) and \(y\). The dominant \(Y\) allele results in green color, whereas the homozygous presence of the recessive \(y\) allele causes the plant to appear yellow. In a testcross between a plant of unknown genotype and phenotype and a plant that is homozygous recessive for both traits, the following progeny were obtained: $$\begin{array}{lc} \text { colored, green } & 88 \\ \text { colored, yellow } & 12 \\ \text { colorless, green } & 8 \\ \text { colorless, yellow } & 92 \end{array}$$ Explain how these results were obtained by determining the exact genotype and phenotype of the unknown plant, including the precise arrangement of the alleles on the homologs.

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?

In a series of two-point mapping crosses involving five genes located on chromosome II in Drosophila, the following recombinant (single-crossover) frequencies were observed: $$\begin{array}{lc} p r-a d p & 29 \% \\ p r-v g & 13 \\ p r-c & 21 \\ p r-b & 6 \\ a d p-b & 35 \\ a d p-c & 8 \\ a d p-r g & 16 \\ v g-b & 19 \\ v g-c & 8 \\ c-b & 27 \end{array}$$ (a) Given that the adp gene is near the end of chromosome II (locus 83 ), construct a map of these genes. (b) In another set of experiments, a sixth gene, \(d\), was tested against \(b\) and \(p r\) $$\begin{array}{ll} d-b & 17 \% \\ d-p r & 23 \% \end{array}$$ Predict the results of two-point mapping between \(d\) and \(c, d\) and \(v g,\) and \(d\) and \(a d p\)
See all solutions

Recommended explanations on Biology Textbooks

Bioenergetics

Read Explanation

Ecological Levels

Read Explanation

Responding to Change

Read Explanation

Cellular Energetics

Read Explanation

Reproduction

Read Explanation

Cell Communication

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free