Genetic Recombination and Gene Mapping

In this video Paul Andersen explains how the frequency of recombination between linked genes can be used to determine the relative location of genes on a chromosome. Thomas Hunt Morgan and Alfred Strutevant used the fruit fly to develop a theory of chromosomal inheritance and discover crossing over.
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All of the images are licensed under creative commons and public domain licensing:
"File:Drosophila Repleta Lateral.jpg." Wikipedia, the Free Encyclopedia. Accessed March 13, 2014. en.wikipedia.org/wiki/File:Dro....
"File:Morgan Crossover 1.jpg." Wikipedia, the Free Encyclopedia. Accessed March 13, 2014. en.wikipedia.org/wiki/File:Mor....
"File:Thomas Hunt Morgan.jpg." Wikipedia, the Free Encyclopedia. Accessed March 13, 2014. en.wikipedia.org/wiki/File:Tho....
"FlyBase," n.d. flybase.org/reports/FBgn000397....
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[@Tomozaurus]

I swear these videos are 100% times better than the actual lectures from my university-run units. They should just show these.

[@mack_raymond]

I have done the majority of my learning on KZbin, for free and in half the time as in lecture. Yet I am paying enormous amounts of money for tuition. This is sad. The only redeeming quality of the school system that I can find is that it pressures me into learning the material for exams. If I didn't have that pressure, perhaps I wouldn't be bothered to learn the material.

[@shadowkisss1958]

funny you mention that cause we are mostly put on to watch his videos in my grade 12 Biology classes

[@theongraham3394]

A million times better than my lecturer!

[@megha7564]

Tom Parker def

[@jessrider2711]

Agreed. I've already learned more from him in a week than this entire semester.

[@samaalnassiry7541]

I haven't watched Bozeman science since my senior year of HS AP biology class. Here I am, 5 years later in college watching him again. Thanks for getting me one degree and on the way to the second.

[@LXRY]

im in senior year ap bio right now lol. good luck on your next degree!

[@AlmostAnything]

HELPFUL ? IT WAS WAS MORE THAN HELPFUL

[@rheannesantos458]

trueee

[@kirillkondrachov4864]

Exam tomorrow, and I now understand all of this. Bless your soul.

[@karinabuhaya5878]

good luck! hope u did well back then

[@fernsader9261]

​@@karinabuhaya5878 unfortunately he's not with us anymore because of this class

[@keishabencosme8491]

Same here

[@blessdog5392]

Blows off his homework. FIres up his pipe, and figures the whole thing out. Studivent was bad 2 the bone

[@sohoyankee66]

I'm running out and buying a pipe. Maybe then I'll understand this. :-)

[@crownofall]

Sounds like me only i prefer a cigarette

[@NobleVagabond2552]

Sounds like me right now except I’m just high af tryna study, all I’m saying tho, Alfred sparked the la

[@mayabalaji1020]

Mr. Anderson, Thank you so much for taking the time to post some of the most helpful science videos on youtube! Your time means the world!!

[@hydrogenperoxide7244]

The fact that i understand more about the whole chapter in this 10 minute video than my one and a half hour of lecture is amazing

[@jsscmoran]

Dear Lord... i learned more in this video than in two lectures ...thank you

[@Jo-gj2nr]

It’s 1 AM the night before my AP bio exam, my bio teacher has spent the entire semester talking about her kids instead of teaching us, I want to thank you for being my bio teacher

[@steff4413]

Jo how did you do

[@joebangles9951]

We need to know, how'd it go

[@Jo-gj2nr]

@@joebangles9951 got a three lol

[@kurdweeb599]

@@Jo-gj2nr out of?

[@Jo-gj2nr]

@@kurdweeb599 5, so not so bad

[@whitakerhoskins]

B to A should be 15 map units

[@A169JB]

+Whitaker Hoskins thanks i did pause and i couldnt figure it out...

[@darrrenmk]

+Whitaker Hoskins Realistically you are right but the recombinant frequencies come from a sample which means there is a range of error

[@OShawna23]

Whitaker Hoskins why

[@thea16able]

Thanks I thought I was going crazy

[@sierraslyh6743]

so, when you look at the math behind the gene mapping, one would expect the distance from B-A and A-D to add up to the distance between B-D since A is just a point in between B and D. however, when you look at the numbers 30+25 does not equal 40. hope that helps

[@skennedy918]

I always use Bozeman science when I am stuck on something from a lecture at uni, helps me understand it in a better light and furthers my learning greatly.

[@lauramorganti4129]

Just wanted to say thank you. I watched this video the night before my genetics exam because I was so confused and I scored 100% 😂🙌🏼

[@jennifermccarty7272]

I am so thankful I stumbled upon your channel, this video in particular. My praxis biology content exam is coming up and your videos are a blessing!

[@ShimiVa]

"and i hope that was helpful" yes, yes it was! way more than the 2 hours i had in class today! thanks!! you're amazing!

This video helped me a lot. I just have to consider some issues about the distance of B-A and A-D. Thinking of it mathematically the distance between B-D from the given data is equal to 55 map units which on that note it should be independently assorted. It must have been 10 map units between A-D which would make total sense and the reordering of the gene map. I have to thank you Bozeman for letting us think critically and curiously

[@joshuawhittaker1233]

Your thinking is great, but in reality, his example is OK. It is possible (maybe even likely) there is a mistake and as a teacher he meant to give a simple example that added up nicely, but I think the numbers reveal the reality of genetic mapping. At 8:57 he says "relative map distance", because recombination frequencies accurately tell the ORDER of genes on a chromosome relative to one another, but do not always accurately tell the exact DISTANCE. In other words, sometimes the math doesn't add up. Reasons for numbers that don't add up are several. Double crossovers can result in incorrect distance calculations. Also, not all areas of the chromosome cross-over equally. Some areas are hotspots that have more recombination, and some areas like the centromeres have almost none. The farther apart genes are, the more opportunities there are for inaccuracy in distance calculations based on recombination frequency. Side note: Another obvious reason the numbers don't always add up, though not related to this exact problem, is that some human chromosomes are 200+ map units. This method can only calculate up to 50 map units because recombination frequency can't go over 50%. Genes that are over 50 map units apart on a chromosome will all map as 50% RF. In such a case, we would need more genes to compare that are closer together, or modern gene sequencing techniques. Also see Khan academy (bottom section of article): www.khanacademy.org/science/biology/classical-genetics/chromosomal-basis-of-genetics/a/linkage-mapping

[@Matthew9.__]

@@joshuawhittaker1233 why cant the distance of the chromosome be higher than 50 map units and the recombination frequency between 2 genes must ne lower than 50% ? Not even exactly 50? Why if it's exactly 50, it means that the genes are in different chromosomes?

[@cosmiccaravan9408]

THOSE VIDEOS HAVE ACTUALLY HELPED ME UNDERSTAND AT ONCE ALL THE THINGS MY UNIVERSITY TEACHERS FAILED TO EXPLAIN CLEARLY! THANK YOU SO MUCH!

[@desertman33]

I've taken a number of courses with this concept and did well enough on the tests, but it was only as I watched this video that it really began to truly make sense

[@farhanaahmed7163]

I was so confused in the lecture, this video has helped me so much, all your videos explain perfectly! Thank you very much!

[@vasenainaiteqe7847]

I have my genetics exam tomorrow and this video has really help in thoroughly understanding Chromosomal Inheritance and recombination. Vinaka Fiji Islands

[@er3652]

Amazing video! Explained it in a way that was easy to understand and had excellent visuals to match. Keep more videos coming!

[@UdyKumra]

The only thing I'm going to remember after the AP exam: if you blow off your homework you might make a groundbreaking discovery.

[@vanshpatel9461]

Udy Kumra usohy

[@Joelpenda]

Thank you Professor.You make things really simple and easy to understand.

[@crosbywhittington4879]

Mr.Bozemen you are truly godsent. I stg you a single-handedly getting me through college science at this point. I hope your pillow is always cold on both sides.

[@tamaracoore6079]

i love your videos so much, it gives me hope, I've been watching them since my freshman year now I'm a junior taking genetics, you helped me through BIO1 and 2 now i feel confident about genetics. -Thank you

[@MacyCathleen]

Don't know what I would have done without your videos and Khan academy this quarter! Thank youuuu!

[@GodisGris1]

This was so helpful! I love that you actually used an example och how to solve it

[@Tamang4CA]

for the last gene mapping part. if B to C is 45%, isn't it impossible for A - B (30%) and A-D (25%) to be bigger than 45%?

[@dilftracker]

A-B would be 15% right

[@azuretea7534]

agree

[@chickenwang8786]

yeah I noticed that also

[@r8irtyit664]

Ye...

[@pratibha2551]

i wish you well.7 years ago wow

[@Its2EZbaby]

Very helpful, thank you so much. 1000% times better than my college professors could explain over the course of several lectures.

[@raj10fat]

Explanation was crystal clear, understood the concept. Thanks Paul. Kudos

[@LK-cc4uj]

You are such a great instructor. The visuals were so helpful as well. Thank you!!

[@ladinonyc]

For someone like me. Besides reading the text book( which I don't get) to later watch a video.Your video helped give me a better image of whats been spoken about in class.Thank you.

[@elianasisman9524]

Excellent video, very helpful. I never understood gene mapping until I watched this video. Thanks so much 🙏❤️💕

[@gazw9933]

Damn. Mr Anderson, you make some of the trickier aspects of my degree so easy to learn. Your videos are an asset to my learning. Thank you. And to answer your question. Yes. It was helpful 👍👍

[@tomvolpe6562]

Great video! Two comments. 1) 50% recombination doesn't necessarily imply the genes you're mapping are on different chromosomes. The could just be far apart on the same chromosome or have a recombination hot spot between them. 2) When you discuss recombination between the b and vg you have a green box labeled recombination and red boxes above and below labeled no recombination. I know what you mean but students may think that there is no recombination occurring in these regions. It may be but you just can't see it with the alleles you are tracking. Thanks again for all your hard work making these videos. They are extremely helpful.

[@yvonnechiletmarch798]

yes it does, as a chromatic only represent 50%, so if its more than this is means its not in the same chromatid and therefore chromosome after recombination

[@rgudduu]

recombination is always checked pairwise, is it? Say, i want to find that final mapping of 4 genes a,b,c,d. So we do pairwise, taking 2 phenotypes at a time, and carefully choosing the corresponding flies?

[@Matthew9.__]

I didnt understand ur second one

[@Sabibi420]

I was going over my lecture material for like an hour and was stuck on the recombination frequencies, I'd almost lost all hope until I found this video. You explained it all so well I can finally understand it now, thanks!

[@pris3675]

This is super helpful great job Mr Andersen! Sincerely student trying to pass HL bio

[@phillipkrayterman3008]

Actually just saved my life. You made a hard concept easy to grasp for anyone. Thanks!

[@rev2505]

This less than 10 minute video just helped me understand what my teacher tried to teach me in a 1.5 hour lecture.

[@Pingyer]

I was wondering the internet for hours wondering how this works, and you somehow just flipped a switch in my head. Thank you😂

[@nmss9969]

Thank you for all the biology videos! They are excellent and so helpful.

[@konstantinospanagiotopoulo2927]

Thank you Paul! I was looking for an explanation like this one! Great work thanks again :)

[@Tomteluva82]

most pedagogic teacher ever, awesome video

[@nancysohlberg8150]

Thank you so much! This illustration and connection is EXACTLY what I was looking for!

[@monagpal1842]

We watch your videos in IB Bio HL, and they help a ton! Thanks so much!

[@katharina...]

All excellent teachers should be required by law to make youtube videos :D Thank you for your time Mr Andersen, your contribution is invaluable!

[@kenbessellieu8267]

Just in time for my final next week! Thank you so much, I owe my A in Bio this semester to you! :)

[@cloverring]

OH MY GOG I LOVE YOU THIS SAVED ME! My teacher didn't go through this and just let us read the section on our own since it was only 2 pages but I was so baffled but the whole mapping thing!

[@kingfisher32]

I was confused by my teacher’s lecture today but now I understand the topic!

[@dt71065]

Thank You So Much! Your videos help me a lot! You are the best teacher I've ever seen in my life! :D

[@lianafeng7074]

Mr. Anderson is my lifesaver every time 🙌🏻🙌🏻

[@charityann27]

you and the amoeba sisters have helped me out a lot this semester

[@zujamongullie6544]

After watching Nth number of video on this. Finally I landed on this!!!! And it cleared all my doubt. I feel like I have attained enlightenment. Thank you so much sir

[@madcowzrchewy]

Thankyou for this! You're infinitely more helpful than the so called "teaching academics" at my university.

[@faramund9865]

8:59 There's an issue now though because now B and A aren't 30% apart!

[@sashadecosta3537]

you get it! you have one the internet for today! congrats! hahah! holy cow what a mistake to have been made! omg, could never have been me!

[@lancebryan56]

ive been watching these videos since 11th grade AP bio and they're even helping me now in my 2nd year in undergrad :')

[@rajbhakta9432]

Hey Paul, I noticed at 9:06 that A was placed closer to B when it should be closer to D. Great video by the way, helped a lot!

[@ztzexplorer]

A-B is 15 m.u., not 30. Your sequence of B-A-D-C is right though. But thank you Mr. Anderson. You're an amazing teacher. I use your videos all the time to reinforce concepts in the minds of my AP Bio students. If only I had your talent!

[@joshuawhittaker1233]

In reality, his example is OK. It is possible (maybe even likely) there is a mistake and as a teacher he meant to give a simple example that added up nicely, but I think the numbers reveal the reality of genetic mapping. At 8:57 he says "relative map distance", because recombination frequencies accurately tell the ORDER of genes on a chromosome relative to one another, but do not always accurately tell the exact DISTANCE. In other words, sometimes the math doesn't add up. Reasons for numbers that don't add up are several. Double crossovers can result in incorrect distance calculations. Also, not all areas of the chromosome cross-over equally. Some areas are hotspots that have more recombination, and some areas like the centromeres have almost none. The farther apart genes are, the more opportunities there are for inaccuracy in distance calculations based on recombination frequency. Side note: Another obvious reason the numbers don't always add up, though not related to this exact problem, is that some human chromosomes are 200+ map units. This method can only calculate up to 50 map units because recombination frequency can't go over 50%. Genes that are over 50 map units apart on a chromosome will all map as 50% RF. In such a case, we would need more genes to compare that are closer together, or modern gene sequencing techniques. Also see Khan academy (bottom section of article): www.khanacademy.org/science/biology/classical-genetics/chromosomal-basis-of-genetics/a/linkage-mapping

[@Antweezy]

bless you. this was so much easier to follow than an hour long lecture

[@user-oo8fd2ov5m]

thanks so much what I admire about you lessons that they are deep and focus on the historical background and how did they figure out the thing you are explaining rather than just memorizing without understanding the origin

[@emiliaarif]

whats life without paul andersen... thank u paul ^^

[@jorgeaguilar5809]

OMFG I hope one day I can be as skilled as you to teach science, your videos are GOLD :D

[@krystelnavarro1223]

You are a great teacher and speaker! Thanks for the videos!

[@peacelovejonas094]

Your videos are so helpful! I finally understand this thank you!

[@bullterry14]

thank you! very helpful videos .you are like my second bio teacher.

[@Samanthava]

Absolutely brilliant mate. Clearly presented and you get right to the point I love it. Thanks for the contribution Paul. HD in gentics here i come :).

[@amandashirley990]

The problem you give at the end does not make sense. If the correct order is BADC, as you state, the distance between B-A that you list as 30 mu, and A-D you have listed as 25 mu combined give a combined distance of 55, which would signify that the genes B & D are probably not listed on the same chromosome, and no where near the listed 40 mu's apart. I think the distance between B-A was supposed to have read as 15, not 30, in which case the problem is correct, and the idea that there are 40 map units between B & D is sound.

[@georgeofhamilton]

Arjune Giri Amanda Shirley Maybe he wanted to give us an example of an anomaly of statistics and make us see that this idea still works.

[@BrennanMohrer]

+Amanda Shirley Or maybe he just made a mistake. It happens.

[@noirritnibedita7565]

but I got BADC where A should be 10 units distant from D,here it is shown as 25!

[@dma67111]

noirrit nibedita no its 15mu Total 50mu..longest b-c 45mu So b-a + a-d + d-c (5%) = 45mu and on a 50mu chromosome

[@mouzicanat]

You can't combine the percentages. Assume they never relate in any way.

[@ananyasuri1223]

Omg I don’t have words to explain about this video....I saw a lot and lot of videos but finally understood it .....thanks

[@fmar105]

You explain so many different topics well!

[@matthew_bang]

UC honors bio genetics class. Lectures didn't explain this and textbook didn't bother to explain either. You're my go-to source for bio videos

[@SpycyWonton]

I understand the concept better now, thank you! The only confusing part was the math in the RF example, the numbers don't add up.

[@aliyahstinard3038]

You made me understand in 10 minutes what my professor couldn't over 2 weeks

[@rymunoz]

Thanks Mr. Anderson!!!! Your videos always help me!!

[@meggietiffany9124]

Thank you for being a more understandable source of teaching than my Actual university lecturers

[@debbiewright2259]

This video is very helpful, very clear and concise, thank you!

[@hebahamood362]

my HS teachers traumatized me by making us watch you all the time but I'm so glad I got over it! woohoo ty very helpful

[@shawnagar3747]

Thank you So much KDB... Assisting on and off the Pitch

[@dan-simi6]

The percentages of A-B + A-D = 55% or should I say 55 u.m. Shouldn't = 40 % or u.m.? As the distance from B-D (40%) ........since A is between them hmmmm

[@komals.6881]

Sir you are the best teacher for genetics i would say.. Your vedios have helped me a lot. Thank you so much.

[@drvir]

*videos

[@nicholasevangelinos6962]

This shaved off so much time from my hw, thank you

[@taladiv3415]

Well done dear contributor Paul Andersen!

[@sachinsmalavalli4669]

AWESOME SIR, YOU SIMPLIFIED IT, I'M IN LOVE WITH YOUR VIDEOS...

[@sameepthakuri9550]

I guess studying at one of best university in the world doesn’t necessarily mean you have access to one of the best teachers in the world . Thank you for this

[@hardgoer]

Thank you so much, I was able to understand this topic much better because of this video my text book was so confusing.

[@husseinsa5050]

regarding the problem, I think the distance between A & C is 25% not between A & D. think youu

[@dilanhama9178]

I really enjoy your lectures.. In fact I am looking for them

[@leewonkim3533]

you are the uni lecturer we need but don't deserve

[@user-kc5ye2is9u]

thanks for sharing, very concise and clear, so helpful!

[@alexbjjperez]

Making dummies like me smarter thanks this really helped me out for my genetics class.

[@jennigleason9704]

Bravo! You explain this so well. Thank you

[@SirJaxxSirJaxx]

Wouldn't the range between A & B be 15%? Because if B to D is 40%, subtracting A's 25% should only allow 15 units left over between A & B and not the 30% you have listed.

[@surajmandal5509]

thanku sir this video was more helpful than the schools lecture

[@funnibunni500]

Way better than my crappy genetics teacher at school. Thank you!

[@athiramenon1592]

Thanks a lot Mr.Anderson,I cud finally figure tht out!!It wasn't so tough aftr all...:) Just one doubt,in the exercise tht u gave,shouldn't A be more close to D than B as AD is 25 centimorgan and AB 30 centimorgan? Thanks again!

[@kianagoudarzi1619]

It was super helpful. Thank you for sharing your knowledge here. God bless you

[@lesoul700]

Wow. What a crystal clear explanation. This is beauty. Thank you so much. Thank you.

[@lesoul700]

This helped me a lot!!!

[@merkesem]

Thank you for your explanation. I really appreciate it !

[@itsnyrasworld]

Thank you for your efforts Prof. ❤️❤️

[@stephanneparr1693]

Thanks so much! Seriously helps me grasp this concept

[@danielec.7789]

it's very helpful. Now I am prepared for my test tomorrow. Thanks

[@jitarthatalukdar2229]

Thanks a lot for explaining it is such a simple and fun way