Variation in a Species

[jumb0mumb0]

I thought he said the germ cells don't contain chromosomes. Then how can he donate 1 chromosome from either his mom or dad from his germ cells to fertilize the ova?

[alyosha24601]

If evolution actually happened, why is all DNA degenerating today? Evolution is quack science.

[jumb0mumb0]

At the end of every lecture, only 1 thought comes to mind: Mind Blowing. Just wow.

[ciphoenix]

The theory of evolution has NEVER led to "another species" by this process. See: net4truthusa - dot com and click on the book "Neogenesis" The theory of evolution does NOT pass the empirical test of science - it is a State-sponsored pagan religion.

[jerrywuification]

I have a question sal. Does sexual reproduction created new genes? If not, then mutation is the ultimate source of variation becasue sexual reproduction merely help recombine and spread out the genes within a population. Thanks

[lilyosse094]

this video totally help me in my studies . thanks, sir :)

[TheCoken]

Epiphany!

[pepperfugl]

I hope my future husband is somewhat like you.

[TheYipedo]

Sal, I'd like to correct you on one little thing at 11:35, the homo in homo sapiens is from Latin meaning man (cognate to French homme, Spanish hombre, etc.) while the homo used in homologous or homosexual means same.

[walkerneo]

I love these videos and I'm learning a lot, but I just wanted to say one thing. You described the variations provided for by our DNA as nearly INFINITE. The problem is that we cannot comprehend infinity, so we think of it as a very large number, such as the number of human variants. Nothing, however, can ever be nearly infinite, because it is either finite or not; there is no degree of being infinite.

[camelCaseFTW]

hehe Sal with a green mustache :|D

[fezzii123]

thanks. you're awesome.

[Aleksi535]

Organisms reproducing via asexual reproduction (mitosis) would be unable to battle such deleterious mutations. Overall, this was a good vid, Sal. Very informative, just needs a little more info in there to complete the idea. I guess now I provided it here and we're all good =) take care. Aleksi

[mrdavetail]

@Aleksi535 feel special now? 

[Aleksi535]

@mrdavetail Feel special??? What do you mean???

[Aleksi535]

@mrdavetail Well, I am a biologist! I have already written an email to Sal, expressing my admiration of what he has done... I feel people like him can truly be called "heroes." They are sharing free education, which people pay thousands of dollars to learn in schools, which probably don't even care about them =) People like Sal are trying to spread education across the globe, and even Gods have not been able to do that (if there are any).

[Aleksi535]

@mrdavetail Anyhow, instead of wasting time and space there and here, respectively, why don't you add some information instead of attacking me =) The whole point of macadamia and education is to share knowledge and ideas, and add onto existing knowledge, and I fell I have done that here. So please do the same!

[Aleksi535]

Also, I was amazed that you never mentioned the fact (which is very important in evolutionary and population biology) that sexual reproduction has the ability to battle deleterious mutations and cancel some of their harm to a certain extent. I remember form my upper division genetics class at the university that there were these mice that had a gene that killed them (in homozygous dominant state) even before they were born, thus observing a 2 (A/a):1 (a/a) ratio.

[derbigpr500]

@Aleksi535 He does mention it in his later videos.

[Aleksi535]

@derbigpr500 Cool... haven't seen that one yet =)

[GollaGandaLova]

@Aleksi535 No one careS? Sal is trying to show us the basic ideas. Not turning us into scientists or biologists.

[Aleksi535]

@GollaGandaLova Well, I am a biologist! And I don't know what you're regarding to. I think he does a great job at teaching and that people like him should start their own schools and teach!

[Aleksi535]

As in the case of the fruit fly (Drosophila melanogaster) the phenotype bar-eyed is due to gene duplication of the genes that control eye morphology, which, by no doubt, is brought about via genetic mutation during recombination during meiosis. Thus, sexual reproduction not only combines different traits, but also produces mutations itself. So mutations, whether dependent or independent of sexual reproduction, deserve way more credit than you give them =) if not the same as sex. repro.

[Aleksi535]

There is always polyploidy (3N, 4N, etc.); not to mention errors in DNA replication and translocatons; all processes that produce new genetic forms independent of sexual reproduction. In other words, I produce the colored chips and you arrange (combine) them in different combination. However, it would also be incomplete to say that sexual selection just does a mere job of combination. It doesn't!

[Aleksi535]

@Aleksi535 Why was this comment removed????

[tullywacker]

i just pooped alittle bit

[Mal1234567]

Genetic mutation is not the source of evolution. This is the first wrong Khan video I have seen out of dozens. Mutation results in freaks, it is not any product of adaptation.

[DeltaA118]

So pretty much we're plagiarizing our parents...

[naeemahn]

Also, under normal cell process, is the DNA strand just unwound? or the DNA strand unwounded "and" attached to histones?

[naeemahn]

I had a quick question. Why are the chromosomes divided into 23 sets? Is each 'set' identical to each other? For example is each pair of chromosome # 1 the same as chromosome # 3? Thanks!

[MrMistery101]

"Maybe they will in some other dimension"

[BHleolam]

THANK YOU SO MUCH!

[poopoohed1993]

watching this after my teacher's lectures makes me REALLY understand about these things.

Thank you so much

[topbluffa1]

this proves that the first people was not black and naturally adapted to Africa but their would of been a variation of skin colours and then over time the best features for africa become the majority, and thats why when the environment changes and the people are in Europe the variations now may be more beneficial than the old favourites (which they are because being black in Europe makes you more likely to catch disease like rickets)

[QueenSemiramis]

Octavia Butler reference?? (3 genders)

:D

[o3darkbabycutie]

i wish i discovered ur vids BEFORE i finished bio.. T________T

btw ur very good at explaining bio+chem. :)

[thawestcoast]

Your colorpannel scared the shhh out of me :)

But.... I love your Vids

[vatoburg]

You're the man! Thank you for taking the time out to help, I've used your videos for just about all my upper level biology classes and you've helped every time, thanks again!

[sgtOOX]

since both male and females are needed for sexual reproduction which is the exclusive act that creates the vast variations that are absolutely essential in evolution, seems a bit of an oxymoron considering there were no males or females at the early stages of evolution,when rapid variation was most vital in order to survive the hostile earth.no species would survive let alone evolve into another species entirely at the slow rate of variation that mutation provides.evolution is at odds once again

[gregrutz]

Darwin only had to prove variation is there for evolution to work on, he didn't know about DNA or mutations. Yet he still showed how it works.

Sexual reproduction produces more variation than cloning, that is why it works toward even more vairation and natural selection works better.

[XpliciTTRecords]

Sal would you say that with an increase in homosexual organisms the population of a species can decrease if that is the homosexual organisms under no circumstances desire to mate with members of the opposite sex?

[thekkl]

@XpliciTTRecords Homosexuals naturally die out because they can't make babies with others of the same sex. The only reason there would be so many homosexuals would be because they have been shunned by society, and thus had to pretend they were straight and make children with people of the other sex.

[himanshuds]

Awesome video...thanks..really helped a lot for my 10th board exams....

[aussiepride961]

Doesn't Homo, as in Homo sapiens mean Man, not same?

[yahvinah1]

@aussiepride961 no

[Secretus]

@aussiepride961 Yes it does. This was a little mistake by Sal. "Homo" in "Homo Sapiens" comes from the Latin "Homo", meaning "man, human", not the Greek "homos", meaning "the same".

[looker130]

nice video

[Xinfinitude]

Great video. I just have one question, though. With the crossover of the genes and a chromosome pair, wouldn't there be a chance that the dna strand could be split up half way through a protein's 'coding', making that that coding useless?

[OlivierdeAthos]

Yes. Homologous recombination happens all the time inside the coding sequences of genes. In fact, this is an additional source of variation. For example, imagin you had two different alleles, one of which is mutated (relative to wild-type) in the front part of the gene, and the other allele is mutated in the end part. A "transheterozygote" carrying the double mutation can have an intragenic crossover, creating one wild-type and one double mutant allele.

[JimmayRyzz]

Very good, you gave some seriously useless insight and I'm more then pleased with this video, 5 Stars and you earned my genuine Subscription aswell as support.

[koboricci]

Ten genders! I have trouble keeping even *one* partner. Now we have to have a ten person orgy to reproduce!? :-P

[willmprise]

sal s right, cystic fibrosis and tay sachs disease are linked to a failure of one gene sequence

[armpitpuncher]

Hey Sal. I think the analogy to a computer program was a little off. From my understanding, if you introduce a random mutation it won't usually break the whole organism, only that protein. This is because of the start and stop codons.

[khanacademy]

Depends on how drastic the mutation is and how important that gene/protein is to the organism. To your point, however, DNA does have more redundancy and fault tolerance than most computer programs (and is far, far, far more complex)

[Valefarous]

For that matter, a lot of computer programs are somewhat fault tolerant, at least the really big ones where you have tons and tons of coders. Hence 'patches' and 'bugfixes' =)

[Trangalanga]

how much time does a computer program last vs a human body if its not designed by humans?

[Trangalanga]

identity vs adaptability

[XpliciTTRecords]

@khanacademy I agree with sal on the the dependency to how important the protein is to the organism eg sickle cell one > one "wrong" protein and well death of the individual can occur

[Magarmach09]

greatest explainations i had ever seen,most simple

i am not from science background so it became diffcult for me to understand these things but these videos explain evolution in best and simple way.

thanks brother ,i am from india new delhi.

i want to know about evolution,i am an atheist

[Prodigyexam12]

Wonderful.

[DNP264296]

1st comment!