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A female heterozygous drosophila melanogaster with the x linked genes of singed bristles (sn), crossveinlesss wings (cv), and vermillion eye colour (v) is testcrossed with a singed, crossveinless, vermillion male and the following progeny were obtained:

1 singed, crossveinless, vermillion 3
2 crossveinless, vermillion 392
3 vermillion 34
4 crossveinless 61
5 singed, crossveinless 32
6 singed, vermillion 65
7 singed 410
8 wildtype 3

total 1000

a) what is the order of these genes on the X chromosome
b) what are the genetic map distances between sn & cv; sn & v; and cv & v
c) what is the coefficient of coincidence

I need a lot of detailed explanations.

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In drosophila, sex is determined by the number of X chromosomes. In this question, since they didn't tell us how many X's each fly has, we can assume that the female has 2 X chromosomes, and the male has 1.

We know that the female is heterozygous, so she has different alleles for each gene on her 2 X chromosomes. The male only has one copy of each gene. I know that vermillion eyes and crossveinless wings are both recessive genes, and I can only assume that singed bristles are as well. So, a fly can only show these traits if they only have the recessive allele (symbolized below using a -) and not the dominant allele (symbolized below using a +).

The alleles can be symbolized as:
sn- = singed bristles
sn+ = non-singed bristles
cv- = crossveinless wings
cv+ = wings with crossveins
v- = vermillion eyes
v+ = non-vermillion eyes

The female has genotype sn+ sn- cv+ cv- v+ v- She is wild-type.

The male has genotype sn- cv- v- He is singed, crossveinless, and vermillion.

a) what is the order of these genes on the X chromosome?

There ...

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See Also This Related BrainMass Solution

Genetics (DNA, Mutations, Cell Division, Protein Synthesis): Punnet squares, mendelian genetics, blood types, and mitosis.

Part 1: Genetics Problem- Human Blood Types

Mendel is the father of modern genetics, but there are some genetic characteristics that cannot be explained by simple Mendelian genetics. Such is the case with the human blood types in which there are 3 alleles for the same gene, A B, and o. A parent can pass allele A, B, or o to the offspring based on the parent's genotype.

From these 3 alleles, there are 4 blood types (phenotypes): A, B, AB, and O, and there are six genotypes: AA, Ao, BB, Bo, AB, or oo. This is an example of codominance in which both A and B alleles are codominant to each other.

Blood types can be used in forensics to determine if blood is from the victim or criminal. Blood types can be used to determine parental source in situation where the father is unknown; however, blood types can only eliminate certain blood types. DNA fingerprinting is a better method that is used often in criminal and parental determination cases.

A o

A

B

Punnett squares such as the one shown above are used to determine the probabilities (percentages) for genotypes of offspring given specific genotypes for the parents.

A) In the example above, the Punnett Square represents a cross (mating) between a male (on the left side) with blood type AB, and a female, (top of square), with blood type A, genotype Ao.

Answer the following for the cross represented above.

1) What are the possible blood types for the offspring?

2) What are the ratios or percentages for each possible blood type from this cross?

3) What blood type is not possible from this cross?

B) Fill out two Punnett squares for a cross between a male with blood type B and a female with blood type AB. (Note that we do not know if the father is genotype BB or Bo from the information given. Thus there are two solutions to the possible cross.)

Set up two Punnett squares and answer the following questions about them.

1) What are the possible blood types for the cross between the type B (BB or Bo?) male and AB female?

2) What are the percentages (%) or probabilities for each blood type in the offspring?

3) What blood type(s) would not be possible in a cross between these two parents?

Hint: There are two answers for questions 1 & 2 above and only one for 3.

Turn in the Punnett Squares and your answers to the questions.

Part 2 : Cell division, mutations and genetic variability.

Eukaryotic cells can divide by mitosis or meiosis. In humans, mitosis produces new cells for growth and repair. And, meiosis produces sex cells (gametes), called sperm and eggs. Changes or mutations in genes in sex cells can be inherited by human offspring. Genetic variation in a population of organisms is good; however, sometimes mutations can be harmful or cause genetic disorders.

Briefly, answer the following questions:

How do meiosis and sexual reproduction (fertilization) produce offspring that differ genetically from the parents?

Describe one example of a human disorder that is inherited and also describe the specific inheritance pattern. For this example, pick disorders that result from mutations in DNA or chromosome number rather than examples such as a genetic tendency for a disorder such as cancer.

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