/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 22 You have a Drosophila line that ... [FREE SOLUTION] | 91影视

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Chapter 4: Problem 22

You have a Drosophila line that is homozygous for autosomal recessive alleles \(a, b,\) and \(c,\) linked in that order. You cross females of this line with males homozygous for the corresponding wild-type alleles. You then cross the \(\mathrm{F}_{1}\) heterozygous males with their heterozygous sisters. You obtain the following \(F_{2}\) phenotypes (where letters denote recessive phenotypes and pluses denote wild-type phenotypes): \(1364+++365\) a \(b c, 87 a b+, 84++c\) \(47 a++, 44+b c, 5 a+c,\) and \(4+b+\) a. What is the recombinant frequency between \(a\) and \(b\) ? Between \(b\) and \(c ?\) (Remember, there is no crossing over in Drosophila males. b. What is the coefficient of coincidence?

Short Answer

Expert verified
Recombination frequencies: 13.1% (a-b), 5% (b-c); coefficient of coincidence: 0.687.

Step by step solution

01

Understand the Exercise

We are dealing with a genetic problem involving linked genes in Drosophila, which are inherited in a specific pattern. The goal is to find the recombination frequency between genes and calculate the coefficient of coincidence.
02

Determine Parental and Recombinant Types

Recognize that parental types for this dihybrid cross will include the most common phenotypes, which are "+ + +" and "a b c" (1364 and 365 individuals, respectively). Recombinant types are all others.
03

Count Recombinant Individuals for a-b and b-c

For genes a-b, recombinants are: "a b +", "++ c", "a++", and "+ bc". Sum these: - 87 (a b +) + 84 (++c) + 47 (a++) + 44 (+bc) = 262. For genes b-c, recombinants are: "a++", "+bc", "a+c", and "+b+". Sum these: - 47 (a++) + 44 (+bc) + 5 (a+c) + 4 (+b+)= 100..
04

Calculate Recombination Frequency

To find recombination frequency, use:\[ \text{Recombination Frequency} = \frac{\text{Number of Recombinants}}{\text{Total Number of Offspring}} \times 100\% \]The total number of offspring is 2000 (sum of all given counts).- For a-b: \( \frac{262}{2000} \times 100\% = 13.1\% \)- For b-c: \( \frac{100}{2000} \times 100\% = 5\% \)
05

Calculate the Coefficient of Coincidence

First, calculate the expected double recombinants based on the independent probabilities:- Product of individual recombination frequencies \((0.131 \times 0.05 = 0.00655)\)- Expected double recombinants: \(0.00655 \times 2000 = 13.1\)Observed double recombinants: 5 ("a c +") + 4 ("+ b +") = 9.Coefficient of coincidence:\[ \text{Coefficient of Coincidence} = \frac{\text{Observed Double Recombinants}}{\text{Expected Double Recombinants}} = \frac{9}{13.1} \approx 0.687 \]
06

Conclusion

The recombination frequency between genes a and b is 13.1%, and between b and c is 5%. The coefficient of coincidence is approximately 0.687.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Recombination Frequency
Recombination frequency is a fundamental concept in genetics that helps understand how often crossovers occur between genes. It involves calculating how frequently different genes are recombined during the formation of gametes. In our exercise with Drosophila, this measurement helps to determine the genetic distance between linked genes. If two genes are far apart on a chromosome, they are more likely to recombine. Conversely, genes close together are less frequently recombined. The formula to calculate recombination frequency is:
\[\text{Recombination Frequency} = \frac{\text{Number of Recombinants}}{\text{Total Number of Offspring}} \times 100\%\]
In the Drosophila problem:
  • For genes \(a\) and \(b\), the frequency was found to be \(13.1\%\).
  • For genes \(b\) and \(c\), the frequency was \(5\%\).
These percentages indicate how often these genes are recombined, reflecting their relative positions in the genome.
Drosophila Genetics
Drosophila, commonly known as fruit flies, are a model organism in genetic studies due to their simple genetic makeup and short life cycle. In Drosophila genetics, researchers often study autosomal recessive alleles to observe inheritance patterns. One particular aspect of Drosophila genetics is that there is no crossing over in male fruit flies. This means that in genetic crosses involving Drosophila, recombination events can only occur in females.
When dealing with linked genes in Drosophila, scientists analyze parental and recombinant phenotypes in offspring to determine which genes are inherited together and which are not. In the exercise, parentals are the phenotypes like "+++" and "abc", and recombinants like "a b +" or "+b+" reflect new genetic combinations formed due to crossing over in females.
Understanding these genetic principles is key for genetic mapping, which helps identify the location of specific genes on chromosomes.
Coefficient of Coincidence
The coefficient of coincidence is a measure used to study genetic linkage by comparing observed versus expected double crossover events. In genetic mapping, double crossovers occur when two separate crossover events happen between three linked genes. The expected number of these events is calculated using the independent probabilities of each single crossover:
\[\text{Expected Double Recombinants} = (\text{Recombination Frequency of } a-b) \times (\text{Recombination Frequency of } b-c) \times \text{Total Offspring}\]
The coefficient of coincidence is calculated as:
\[\text{Coefficient of Coincidence} = \frac{\text{Observed Double Recombinants}}{\text{Expected Double Recombinants}}\]
  • A value close to 1 indicates that the observed and expected numbers of double recombinants are similar, suggesting no interference.
  • A value less than 1, as in the exercise example with \(0.687\), indicates interference, meaning fewer double crossovers occur than expected.
This concept is critical for understanding the physical closeness and interaction of genetic markers.

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Most popular questions from this chapter

For an experiment with haploid yeast, you have two different cultures. Each will grow on minimal medium to which arginine has been added, but neither will grow on minimal medium alone. (Minimal medium is inorganic salts plus sugar.) Using appropriate methods, you induce the two cultures to mate. The diploid cells then divide meiotically and form unordered tetrads. Some of the ascospores will grow on minimal medium. You classify a large number of these tetrads for the phenotypes ARG(arginine requiring) and \(\mathrm{ARG}^{+}\) (arginine independent) and record the following data: $$\begin{array}{cc} \begin{array}{c}\text { Segregation } \\\\\text { of ARG }^{-}: \mathrm{ARG}^{+}\end{array} & \begin{array}{c}\text { Frequency } \\\\(\%)\end{array} \\\\\hline 4: 0 & 40 \\\3: 1 & 20 \\\2: 2 & 40 \\\\\hline\end{array}$$ a. Using symbols of your own choosing, assign genotypes to the two parental cultures. For each of the three kinds of segregation, assign genotypes to the segregants. b. If there is more than one locus governing arginine requirement, are these loci linked?

In the plant Arabidopsis, the loci for pod length (L, long; 1, short) and fruit hairs ( \(H,\) hairy; \(h,\) smooth) are linked 16 m.u. apart on the same chromosome. The following crosses were made: (i) \(L H / L H \times l h / l h \rightarrow F_{1}\) (ii) \(L h / L h \times l H / l H \rightarrow F_{1}\) If the \(\mathrm{F}_{1}\) 's from cross i and cross ii are crossed, a. what proportion of the progeny are expected to be \(l h / l h ?\) b. what proportion of the progeny are expected to be \(L h / l h ?\)

In a tetrad analysis, the linkage arrangement of the \(p\) and \(q\) loci is as follows: Assume that ' in region i, there is no crossover in 88 percent of meioses and there is a single crossover in 12 percent of meioses; in region ii, there is no crossover in 80 percent of meioses and there is a single crossover in 20 percent of meioses; and - there is no interference (in other words, the situation in one region does not affect what is going on in the other region) What proportions of tetrads will be of the following types? (a) \(\mathrm{M}_{\mathrm{I}} \mathrm{M}_{\mathrm{I}}, \mathrm{PD} ;\) (b) \(\mathrm{M}_{\mathrm{I}} \mathrm{M}_{\mathrm{I}}, \mathrm{NPD} ;(\mathrm{c}) \mathrm{M}_{\mathrm{I}} \mathrm{M}_{\mathrm{II}}, \mathrm{T} ;(\mathrm{d}) \mathrm{M}_{\mathrm{II}} \mathrm{M}_{\mathrm{I}}, \mathrm{T} ;\) (e) \(\mathrm{M}_{\mathrm{II}} \mathrm{M}_{\mathrm{II}}, \mathrm{PD} ;(\mathrm{f}) \mathrm{M}_{\mathrm{II}} \mathrm{M}_{\mathrm{II}}, \mathrm{NPD} ;(\mathrm{g}) \mathrm{M}_{\mathrm{II}} \mathrm{M}_{\mathrm{II}}, \mathrm{T}\). (Note: Here the M pattern written first is the one that pertains to the \(p\) locus.) Hint: The easiest way to do this problem is to start by calculating the frequencies of asci with crossovers in both regions, region i, region ii, and neither region. Then determine what \(\mathrm{M}_{\mathrm{I}}\) and \(\mathrm{M}_{\mathrm{II}}\) patterns result.

Use the Haldane map function to calculate the corrected map distance in cases where the measured \(\mathrm{RF}=5 \%\) \(10 \%, 20 \%, 30 \%,\) and \(40 \% .\) Sketch a graph of RF against corrected map distance, and use it to answer the question, When should one use a map function?

In a haploid fungus, the genes \(a l-2\) and \(a r g-6\) ar apart on chromosome \(1,\) and the genes \(l y s-5\) \(a l-2+;+m e t-1 \times+\arg -6 ; l y s-5+\) what proportion of progeny would be prototrophic \(++\) \(++?\)
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