How to solve problems with crossing over, map units and centiMorgans

The percent recombination between two markers indicates the map distance between them: 1% recombination = 1 map unit (m.u.).
In genetic genealogy, a centiMorgan (cM) or map unit (m.u.) is a unit of recombinant frequency which is used to measure genetic distance. It is often used to imply distance along a chromosome, and takes into account how often recombination occurs in a region.

[@GeneticsLessons]

Here is one more practice problem chromosome costing-over explained: ua-cam.com/video/z_SficZw56c/v-deo.html

[@thejac4098]

Thank you bro😊😊 for all the efforts you take in making the video and thn explaining them.

[@nesnoesa]

Great explanation! Thank you for all the effort

[@GeneticsLessons]

Glad it was helpful!

[@fateme7799]

Thank you! That was quite helpful for me!

[@GeneticsLessons]

Glad it helped!

[@shailendramishra2099]

I am student of class 12 from india. this was verymuch helpfully. keepdoing this.

[@arpitahota1131]

Hi Nikolay, I have a question. If two DCOs are found, and the total percentage is 0.5, then how the percentage of gamete ABC alone can have 0.5? I think the value should be 0.25%, what do you think?

[@preetiyadav7225]

Yes same doubt!!
Did you know the correct answer?

[@arpitahota1131]

@preeti the answer should be 0.25%

[@preetiyadav7225]

Okay got it!
Thank you

[@palwindersingh1398]

It's 0.25 if it have no interface

[@GeneticsLessons]

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[@titoflash1212]

Nikolay thx a lot, o nearly understand the topic.
I have doubt with the diagrams of crossing over, on hoje to know if what i an moving are two genes or one

[@GeneticsLessons]

Usualy hundreds of genes are switching chromosomes, we ignore all except of genes our interest.

[@Jasleen_kaur13]

Nice explanation bro 😃...really helpful for an neet aspirant ..keeo it up ❤️

[@GeneticsLessons]

Thank you, I will

[@priyankapal1442]

Can you plz make a video on this question...
What will be the percent frequency of AB/ab(or ab/ab) individuals in the test cross,if there is 10% recombination and the linkage is in coupling phase.

[@GeneticsLessons]

I do not understand this question the way it is formulated have to be some kind of mistake.

[@MrYahya0101]

But the distance between the genes are due to double crossovers AND single crossovers. So when you multiply the two distances you're also including single crossovers. For example the 10 map units between A and B is calculated as: (ABc + abC + ABC + abc)/total. So multiplying the 10% * 5% includes double crossovers AND single crossovers. Correct me if I'm wrong.

[@GeneticsLessons]

No initial distance between genes are calculated only based on crossing over frequencies between two genes. So in order to calculate double cross-over frequency we just have to multiply individual probabilities.

[@MrYahya0101]

@@GeneticsLessons Look at how the distance is calculated here (under "three-point crosses"): mcb.berkeley.edu/courses/mcb142/lecture%20topics/Amacher/LECTURE_5_LINKAGE2_F08.pdf
They include the single and double crossovers in calculating the distance.

[@GeneticsLessons]

You mess gene mapping and distance calculation in simple school problem. I'm using information that is given in the problem. In this problem there is NO table of three genes crossing over frequency is given. No double-crosses is given. So how do you suppose I will include them in my calculations?

[@khushijaswal]

@@GeneticsLessons yes sir. you're right.

[@dibyajyotisrpattanayak6959]

Nicely explained !! 👏👏

[@GeneticsLessons]

Glad it was helpful!

[@meiniparnes8488]

QUESTION: Shouldn't it be 0.5% x 0.5 because HALF of the gametes would have ABC and the other have abc?

[@GeneticsLessons]

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[@sanoverkhan9945]

can you please tell how 1/20 calculated?

[@GeneticsLessons]

50% is 1/2
10% is 1/10
5% is 1/20
1% is 1/100

[@yoursexycookie]

You can also think of it as a proportion... *if 100% is 1 and 0% is 0:*
So you multiply 0,1 (10%) x 0,05 (5%) = 0,005 which is 0,5%

[@Learn-inspire]

Great

[@bigboysam8350]

Superb 😊

[@GeneticsLessons]

Thanks for liking

[@RahulDas-ej9hc]

In a diploid organism, these Gene's A,B and C are present on the same chromosome in that order. The AB interval is 10 map unit and BC interval is 20 map unit. In AaBbCc heterozygous individual, what will be the proportion of gamet that carry the genotype AbC ?
A- 1%
B- 10%
C- 20%
D- 30%
Make a video of it Plz...

[@GeneticsLessons]

Ok, will make a video.

[@RahulDas-ej9hc]

Thank You Very Much...

[@GeneticsLessons]

Here is solution: ua-cam.com/video/z_SficZw56c/v-deo.html

[@RahulDas-ej9hc]

Then ua-cam.com/video/_fJdeGKKxgc/v-deo.html Here the result should be 0.25 Which is not given.

[@GeneticsLessons]

@@RahulDas-ej9hc Yes, will remake this video, thank you for notifying.

[@flyingbirds1845]

Percentage of parental gametes ?

[@GeneticsLessons]

What do you mean? They are always 50/50

[@flyingbirds1845]

Sir, If follow the same rule... percentage of parental
90/ 100 × 95 /100
= 0.9 × 0.95 = 0.855 = 85.5 %
Other recombinants, ABc/ abC= 0.1 × 0.95 = 0.095 = 9.5 %
Abc/aBC = 0.9 × 0.05 = 0.045 = 4.5 %.
ABC/abc= 0.1 × 0.05 = 0.005 = 0.5 %
85.5 + 9.5 + 4.5 + 0.5 = 100 %
But que asking about only ABC, so why not 0.5/2 = 0.25

[@thejac4098]

Plz solve them

[@GeneticsLessons]

One of them again contains a mistake but at least has close number as an answer.

[@sankhadipdas3500]

200 cM is the most valuable part

[@GeneticsLessons]

Maximum distance between 2 genes can be 50 cM.

[@prachishekhawat1094]

Very easy

[@GeneticsLessons]

Thanks a lot 😊