Question

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 \(a d p\)

Short answer

Answer: The predicted recombinant frequencies between gene \(d\) and the other genes are: - \(d-c\): \(44\%\) - \(d-v g\): \(52\%\) - \(d-a d p\): \(71\%\).

Step-by-step solution

Examine the given recombination frequencies

First, write down the recombination frequencies for all gene pairs: \((p r-a d p, 29), (p r-v g, 13), (p r-c, 21), (p r-b, 6),\) \((a d p-b, 35), (a d p-c, 8), (a d p-r g, 16), (v g-b, 19), (v g-c, 8), (c-b, 27).\)

Determine gene order and distances

Determine the gene order using the given recombination frequencies. The order of the genes should be based on the principle that the sum of the recombination frequencies should be minimized. From the given frequencies, we can begin with \(p r\) as the first gene. There are three distances involving \(p r\): \(p r-a d p\), \(p r-v g\), and \(p r-c\). Since the smallest distance is with \(p r-b\) (\(6\%\)), \(b\) should be the closest to \(p r\). We can arrange the other genes in a linear order by observing distances between them: \(p r - 6 - b - 27 - c - 8 - v g - 19 - a d p - 29 - r g\) The positions of \(d\) are given as: \((d-b, 17), (d-p r, 23).\)

Determine recombination frequencies between \(d\) and the other genes

Predict the recombinant frequencies between \(d\) and other genes by observing their distances on the map: Between \(d\) and \(c\): \(d - 17 - b - 27 - c\) Recombination frequency: \(17 + 27 = 44\%\) Between \(d\) and \(v g\): \(d - 17 - b - 27 - c - 8 - v g\) Recombination frequency: \(17 + 27 + 8 = 52\%\) Between \(d\) and \(a d p\): \(d - 17 - b - 27 - c - 8 - v g - 19 - a d p\) Recombination frequency: \(17 + 27 + 8 + 19 = 71\%\) The predicted recombinant frequencies between \(d\) and other genes are: \(d-c\): \(44 \%\) \(d-v g\): \(52 \%\) \(d-a d p\): \(71 \%\).

Key concepts

Gene Mapping

Gene mapping is the process used to determine the specific position of genes on a chromosome. It's a crucial part of genomics, which helps scientists understand the relationship between genes and their physical locations. This becomes important in genetic studies and in understanding inherited traits.

• Gene mapping not only helps in pinpointing where genes are located but also in predicting how they may be inherited across generations.
• In the context of Drosophila, or fruit flies, gene mapping is often used due to their simple genetic structure and the ease with which their genes can be manipulated and observed.
• The knowledge of specific gene locations aids in identifying possible genetic mutations and can provide insights into human genetics and diseases.

Through recombination frequencies, which are observations of how often genes swap places during reproduction, gene positions can be mapped. These frequencies indicate how closely genes are linked; the lower the frequency, the closer together they are likely to be on the chromosome.

Chromosome II

Drosophila, commonly known as fruit flies, serve as a model organism in genetics due to their well-defined chromosomes. Chromosome II is one of the key focus areas in many genetic studies of Drosophila.

• Chromosome II is composed of an extensively studied collection of genes that control various traits and functions in the fruit fly.
• In the context of this problem, understanding recombination frequencies on Chromosome II helps scientists build a genetic map to predict how genes are associated with each other.
• Mapping exercises often involve cross-breeding experiments, where different genotypes are crossed to analyze the offspring for signs of recombination, giving clues about gene order on Chromosome II.

In practical terms, knowing the details of Chromosome II can be a gateway to unravel complex genetic interactions, understanding evolutionary relationships, and providing a foundation for advanced studies in genetic manipulation and biotechnology.

Recombination Frequency

Recombination frequency is a key concept in genetics that refers to the percentage of offspring that inherit a new combination of alleles, different from the parental combination. This occurs because of crossing over during meiosis, where homologous chromosomes exchange segments.

• Recombination frequency is calculated by dividing the number of recombinant offspring by the total number of offspring, then multiplying by 100 to get a percentage.
• This percentage is crucial in determining the genetic map distance between two genes. A lower recombination frequency suggests genes are closer together on a chromosome.
• In Drosophila studies, recombination frequencies allow researchers to build genetic maps to monitor how traits and genes are inherited through generations.

In our exercise, understanding recombination frequencies between different gene pairs on Chromosome II allows for the construction of a gene map which visualizes the chromosomal layout. It also helps in predicting functional traits and understanding the genetic framework of organisms.