Because of the relatively high frequency of meiotic errors tha...

Question

Because of the relatively high frequency of meiotic errors that lead to developmental abnormalities in humans, many research efforts have focused on identifying correlations between error frequency and chromosome morphology and behavior. Tease et al. (2002) studied human fetal oocytes of chromosomes 21, 18, and 13 using an immunocytological approach that allowed a direct estimate of the frequency and position of meiotic recombination. Below is a summary of information that compares recombination frequency with the frequency of trisomy for chromosomes 21, 18, and 13.

What conclusions can be drawn from these data in terms of recombination and nondisjunction frequencies? How might recombination frequencies influence trisomic frequencies?

Table comparing chromosomes 21, 18, and 13 showing mean recombination frequencies and live-born trisomy rates.

What conclusions can be drawn from these data in terms of recombination and nondisjunction frequencies? How might recombination frequencies influence trisomic frequencies?

Accepted Answer

Hi everyone. Let's look at our next problem. It says a wild type fruit fly. Hetero zig. It's for it's brown body color and red eyes is mated with a black bodied fruit fly with brown eyes. The offspring have the following fanatic distribution. And we've got numbers of offspring in four different types. Brown body with red eyes, brown body with brown eyes, brown or black body with red eyes and black body with brown eyes, calculate the recombination frequency between the genes for body color and eye color. Well, calculating the recombination frequency, we have a formula for this. Pretty straightforward. So recombination frequency in percent equals the number of recombinant offspring divided by the total number of offspring times 100. So, first we have to calculate how many recombination offspring we have. So since our parents, parental types are brown body with red eyes, and black body with brown eyes are competent offspring are brown body with brown eyes, and black body with red eyes. So that's gonna be 780 plus 156. This gives us rick competent offspring. We're gonna need to divide that by the total number of offspring. So that's all four of these numbers here, 770 plus 780 plus 156 plus 160. And those four numbers added together are going to give us 1,866. So to calculate our recombination frequency, we're then gonna have 986 are number of recombinant offspring divided by 1866. Our total number of offspring times And this gives us our recombination frequency and %. 50.2%. When we look at our answer choices, we see the choice fee is 50%. Now, of course. One interesting side note about a recombination frequency of 50% is that that means that our genes for body color and eye color are either very far apart, on the same chromosome or on different chromosomes. Um a recombination of 50% indicates that any less recombination frequency. A smaller number would indicate that the two genes are linked on the same chromosome. But in this case there either as far apart as they can be or their own separate chromosomes. With that recombination frequency that we calculated between these genes of choice. D 50%. See you in the next video.

Key Concepts

Meiotic Recombination

Nondisjunction

Trisomy

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