In Drosophila, three autosomal genes have alleles as...

In Drosophila, three autosomal genes have alleles as follows: Gray body color (G) is dominant over black ( $g$ ). Normal wings $(A)$ is dominant over vestigial $(a)$ Red eye $(R)$ is dominant over sepia $(r)$ Two crosses were performed, with the following results: Cross I: Parents: heterozygous red, normal $\times$ sepia, vestigial Offspring: 131 red, normal 120 sepia, vestigial 122 red, vestigial 127 sepia, normal Cross II: Parents: heterozygous gray, normal $\times$ black, vestigial Offspring: 236 gray, normal 253 black, vestigial 50 gray, vestigial 61 black, normal Are any of the three genes linked on the same chromosome? If so, what is the distance between the linked genes (in map units)?

In Drosophila, three autosomal genes have alleles as follows:
Gray body color (G) is dominant over black ( $g$ ). Normal wings $(A)$ is dominant over vestigial $(a)$ Red eye $(R)$ is dominant over sepia $(r)$ Two crosses were performed, with the following results:
Cross I:
Parents: heterozygous
red, normal $\times$ sepia, vestigial
Offspring: 131 red, normal
120 sepia, vestigial
122 red, vestigial
127 sepia, normal
Cross II:
Parents: heterozygous
gray, normal $\times$ black, vestigial
Offspring: 236 gray, normal
253 black, vestigial
50 gray, vestigial
61 black, normal Are any of the three genes linked on the same chromosome? If so, what is the distance between the linked genes (in map units)?

Key Concepts

Genetic Linkage

Genetic linkage refers to the phenomenon where alleles at different loci are inherited together more frequently than expected from independent assortment, due to their close physical proximity on the same chromosome. This closeness reduces the likelihood of a recombination event occurring between them, and their behavior deviates from Mendel’s law of independent assortment.

Recombination Frequency

Recombination frequency is a measure of the proportion of recombinant offspring produced in a cross and is used as an indicator of the physical distance between two linked genes. It is calculated by dividing the number of recombinant progeny by the total number of progeny, and is expressed as a percentage.

Map Units (Centimorgans)

Map units, often called centimorgans (cM), quantify the distance between genes on a chromosome based on their recombination frequency. One map unit is defined as a 1% chance of recombination occurring between two genes, allowing geneticists to construct linkage maps that reflect the relative positions of genes.

Test Cross Analysis

Test cross analysis is a genetic cross performed to reveal unknown genotypes and to study linkage between genes. By crossing heterozygous individuals with homozygous recessive individuals, researchers can observe the phenotypic ratios in the offspring to detect deviations from expected independent segregation, which indicates the presence of linkage.

Transcript

00:01 We can answer this question by looking at each cross individually.

00:05 First, let's set up our crosses.

00:08 The first cross, the parents were heterozygo red normal, so they have a big r, little r, big a, little a, and that parent was crossed with a parent with sepia eyes, so two little r's, and vestigial wings.

00:27 They had the following combinations of offspring.

00:30 They had 131 red normal baby.

00:36 They had 120 sepia vestigial.

00:44 They had 122 red vestigial and they had 127 sepia normal.

01:01 The second cross, the parents had the following genotypes.

01:08 The first parent was gray normal and the question told us that they were heterozygous.

01:16 That individual was crossed with a black vestigial fly, so two little gs for black body and two little a's for vestigial wings.

01:25 And they had the following combinations of offspring.

01:28 They had 236 gray normal offspring.

01:37 They had 253 black vestigial offspring.

01:44 They had 503 black vestigial vestigial offspring and finally they had 61 black body normal winged offspring.

01:59 Now, we've been tasked with trying to determine if either of these genes are linked.

02:06 The way you tell if they are linked is you look at the ratio of parents to offspring.

02:12 So let's just identify our parentals and our recombinants.

02:17 So here you have a parental.

02:21 I'm just going to put a p for parental.

02:23 This one is also a parental.

02:25 If crossing over, you should have combinations of individuals that are present in a different amount than a one -to -one -to -one ratio...

Please give Ace some feedback