Scientists do a testcross of the creatures from problem 4...

Scientists do a testcross of the creatures from problem 4 using heterozygotes for height and nose shape. The offspring are tall/ upturned snout, 41 ; dwarf/upturned snout, $8 ;$ dwarf/downturned snout, $43 ;$ tall/downturned snout, $8 .$ Calculate the recombination frequency from these data, and then use your answer from problem 4 to determine the correct order of the three linked genes.

Key Concepts

Testcross

A testcross involves crossing an individual with an unknown genotype with another that is homozygous recessive for the trait. This allows researchers to reveal the heterozygous traits by observing the offspring phenotypes, which is particularly informative when studying linked genes and determining gene order.

Recombination Frequency

Recombination frequency is a measure of how often crossover events occur between two loci during meiosis. It is used to estimate the physical distance between genes on a chromosome. A higher recombination frequency indicates that the genes are further apart, while a lower frequency suggests they are closer together.

Genetic Linkage

Genetic linkage refers to the phenomenon where genes that are close together on the same chromosome tend to be inherited together. This occurs because the physical proximity of the genes reduces the likelihood that a crossover event will separate them during meiosis.

Gene Order Determination

Gene order determination involves using recombination frequencies from testcross data to infer the relative positions of genes on a chromosome. By comparing the frequencies of recombinant phenotypes, researchers can construct a linkage map that shows the sequential order and approximate distances between the genes.

Transcript

00:01 All right, so we're going to pick up from the last question and look at that last combination of genes, the tall gene or the height gene, with the nose gene.

00:15 So if you'll remember from the last question, at the very end, we came up with the recombination frequencies and then the allelic differences for those.

00:26 So for our height and antenna genes, we determined that those are 12 map units apart.

00:34 The antenna and nose genes we determined were five map units apart.

00:39 So we're going to basically do the same thing that we did in the last question, determining the alleleic or the recombination frequency and using that to get the allelic distance.

00:49 And then we're also going to try to map these genes in order based on those allelic distances that we get for all of them.

00:58 So for this one, we're looking at a test cross with a heterozygous female for height and nose, so being a tall female with an upturned snout, crossed with the male, which has the dwarfism and a downturned snout.

01:21 And these are the offspring that we get.

01:25 So again, we see majorities on the parent types, and then the recombinants have much less.

01:35 So let's first calculate the recombination frequency.

01:41 And so you're going to add up 8 plus 8 for those recombinants, get 16.

01:47 And then this again totals out to 100.

01:50 So 16 divided by 100.

01:53 Is equal to 0 .16 or 16%...