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Chapter 5: Problem 21

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?

Short Answer

Expert verified
Answer: The lack of crossing over and synaptonemal complexes in male Drosophila indicates that their genetic material is passed on to their offspring unchanged, resulting in less genetic variability. Therefore, the majority of genetic diversity in offspring is generated by the female meiosis process.

Step by step solution

01

Understand Crossing Over

Crossing over is a process that occurs during meiosis, where homologous chromosomes exchange portions of their DNA. This process results in the recombination of genetic material, leading to an increase in genetic variability among offspring.
02

Understand Synaptonemal Complexes

The synaptonemal complex is a protein structure formed between homologous chromosomes during meiosis, specifically in the prophase I stage. It holds the chromosomes together and facilitates the exchange of their genetic material during crossing over events.
03

Relationship between Synaptonemal Complexes and Crossing Over

The synaptonemal complex is responsible for the process of crossing over, as it physically holds the homologous chromosomes together and promotes the exchange of their genetic material. This leads to the conclusion that the presence of synaptonemal complexes is directly related to the occurrence of crossing over.
04

Observation 1: No Crossing Over in Male Drosophila

Since there is no crossing over observed in male Drosophila, we can infer that there is no genetic recombination occurring during male Drosophila meiosis. This implies that the genetic material of male Drosophila is passed on unchanged to their offspring.
05

Observation 2: No Synaptonemal Complexes in Males but Present in Females

The absence of synaptonemal complexes in males indicates that the machinery required for crossing over is not present during their meiosis. In contrast, the presence of synaptonemal complexes in females signifies that crossing over occurs during their meiosis, leading to genetic recombination and increased genetic diversity in their offspring.
06

Conclusion 1: Male Drosophila Pass on Unchanged Genetic Material

Since there is no crossing over or synaptonemal complexes observed in male Drosophila meiosis, it can be concluded that their genetic material is passed on to their offspring unaltered. This may result in offspring with less genetic variability as compared to offspring produced through female meiosis, which undergo crossing over.
07

Conclusion 2: Genetic Diversity Majorly Comes from Female Drosophila

As synaptonemal complexes are observed in female Drosophila but not in males, we can conclude that the majority of genetic diversity in offspring is generated by the female meiosis process. This can result in a more diverse and adaptable population, which is important for the survival and fitness of the species.

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Most popular questions from this chapter

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?

Are mitotic recombinations and sister chromatid exchanges effective in producing genetic variability in an individual? in the offspring of individuals?

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

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

Phenotypically wild \(\mathrm{F}_{1}\) female Drosophila, whose mothers had light eyes \((l t)\) and fathers had straw \((s t w)\) bristles, produced the following offspring when crossed with homozygous lightstraw males: $$\begin{array}{lc} \text { Phenotype } & \text { Number } \\ \text { light-straw } & 22 \\ \text { wild } & 18 \\ \text { light } & 990 \\ \text { straw } & 970 \\ \text { Total } &{2000} \end{array}$$ Compute the map distance between the light and straw loci.
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