here are the results of a cross between two flys?

Question

here are the results of a cross between two flys

gray body , normal wings 236
black body, vestigial wings 253
gray body, vestigial wings 50
black body , normal wings 61

what conclusion can you draw about the chromosomal location of these genes ? what proces gives rises to the gray flys with vestigial wings and black flies with normal wings ?

Answer 1

The cross you would do to see this is a test cross in which a strain carrying 1 normal and 1 mutant copy of each gene (total 4 genes) is crossed to a fly having all the recessive alleles present.

even without knowing the genotypes of the parents and grandparents you can tell that the genes involved in each trait (wings and body color) are LINKED because the traits don't segregate independently (what would the ratio be if each allele were on a different chromosome?).

genetic LINKAGE is just the observed phenomenon that some sets of alleles don't obey mendel's laws of independent assortment and segegration. A long time ago a geneticist named Bateson called the phenomenon of linkage "attraction and repulsion" of alleles. Several years later a guy named Morgan - along with his students - showed that linkage was merely a consequence of genes arranged in a line on chromosomes and that how often one pair of linked alleles would become unlinked is a result of the distance separating the two alleles.

based on the latter question, you can infer that if there products of some event (recombination) results in gray/vestigial and black/normal then the genotypes of the grandparents were gray/normal and black/vestigial.

there are some errors in the previous person's explanation. 1st synapsis generally happens BEFORE crossing over although there is evidence that in some animals, if synapsis is not very efficient, crossing over can activated to promote synapsis.

second, the specific concept of a "recombination FREQUENCY" is unnecessary to answer this question (it is important however and i encourage you to learn what it is).

Answer 2

Bb | bb
___|__
bB | BB
|

Okay so when you cross flies with dominant and recessive alleles of genes you get a mix of heterzygous and homozygous progeny. So you will get a 2:1:1 mix 1/4 recessive 1/4 dominant and 2/4 heterozygous. which shows up as 3/4 dominant since thats what is the phenotype for dominant and recesive both and 1/4 recessive which is close to what you have here. This occurs if the genes are not linked ie not close to one another. If they are unlinked they are not near each other on the same chromosome. These data point to these genes being linked or on the same chromosome. The gray flys with vestigial wings and black flies with normal wings indicate recombination has occured in the chromosome.

Answer 3

I'm going to make this as clear as possible.

When two flies or humans or beings mate, their chromosomes are each one set of a pair of chromosomes that determines the genetic makeup of the offspring.

During a process called synapsis, the chromosomes exchange random segments of DNA. This is known as crossing over.

The closer two traits are on the DNA, the more probable it is that the two traits will remain together on the final chromosome. In other words, the two characterisics are linked.

But how do we measure linkage? By something called recombination frequency.

Lets say a male and a female mate and have many offspring. The female happens to have blue eyes and blonde hair. These characteristics are close together on the chromosome, so the offspring are likely to recieve both characteristics together.

Lets say we could modify the chromosome of both parents to move the blue eye and blonde hair genes farther apart on the chromosome. That would mean more of the children have blonde hair and black eyes for example, or black hair and blue eyes for instance. In other words, the traits would recombine in the offspring less frequently. This is what is meant by the term recombination frequency.

Figure it out from what I have said.

Answer 4

The genes must be located on the same chromosome, meaning that the genes are linked. The few flies with the other combinations must have been the result of crossing over during meiosis.

I'd say the genes must be fairly far apart on the chromosome because there are quite a few of the variant phenotypes.

Answer 5

No - eg.it fairly is a a million:2:2:a million:4:2:a million:2:a million genotypic ratio a million/sixteen would be homozygous dominant for the two characteristics (TTRR) 2/sixteen would be homozygous dominant for top and heterozygous for shape (TTRr) 2/sixteen would be heterozygous for top and homozygous dominant for shape (TtRR) a million/sixteen would be homozygous dominant for top and homozygous recessive for shape (TTrr) 4/sixteen would be heterozygous for the two characteristics (TtRr) 2/sixteen would be heteozygous for top and homozygous recessive for shape (Ttrr) a million/sixteen would be homozygous recessive for top and homozygous dominant for shape (ttRR) 2/sixteen would be homozygous recessive for top and heterozygous for shape (ttRr) a million/sixteen would be homozygous recessive for the two characteristics (ttrr) it fairly is a a million:2:2:a million:4:2:a million:2:a million genotypic ratio