drenken: I have a question about quiz 8

Meredith: sure thing

drenken: I don't understand 2 and 11

Meredith: ok - let's look at those

Meredith: hang on one sec

drenken: I don't know how to find the numbers

drenken: ok

Meredith: so the question is on mitosis

Meredith: or, really I should say cell division via mitosis

Meredith: that is the full name of the process

Meredith: do you have your book by the way?

Meredith: do you have your book nearby?

drenken: yeah

Meredith: ok

Meredith: so let's look at p. 130

Meredith: mitosis is just the steps from prophase to telophase (as an aside)

Meredith: but the whole drawing shows cell division via mitosis

Meredith: so there is a step before and one after that complete the full cell cycle

Meredith: we can't see too well in prophase, but if you look at pro-metaphase on p. 130, how many chromosomes are in that cell?

Meredith: or prophase we can see OK I guess, too

Meredith: how many total chromosomes in the example cell?

drenken: 2 or 4

Meredith: ok - and its 4

Meredith: each x-shaped doobie is a chromosome

Meredith: there are 2 little doobies and 2 bigger ones

Meredith: if you look at the very end on p. 131

Meredith: how many chromosomes are ending up in each side of the cell that is fully dividing?

Meredith: count purple strands (and just count for 1 of the dividing cells)

drenken: 8

Meredith: 8 total

Meredith: and 4 will end up in each half

Meredith: agreed?

drenken: yes

Meredith: ok

Meredith: so end of p. 131 is just before cell division is complete

Meredith: so those 2 halves will become 2 different cells

Meredith: each with 4 chromosomes

Meredith: and the parent cell that made them also had 4 chromosomes

Meredith: so, number of chromosomes stays the same

drenken: their identical to the parents?

Meredith: right

Meredith: and that makes sense for what mitosis helps with

Meredith: cell division via mitosis is for taking a normal cell

Meredith: like a toe cell

Meredith: and making a copy - an exact copy - of that toe cell

Meredith: so everything should be the same, including chromosome #

drenken: ok

Meredith: so if a parent cell has 64 chromosomes before cell division via mitosis, each daughter cell would end up with?

drenken: 64 chromosomes

Meredith: yep

Meredith: easy-peasy

Meredith: ok

Meredith: so 11

Meredith: meiosis helps with making babies

Meredith: so, not copying toe cells anymore

Meredith: we are talking future parenthood

drenken: ok

Meredith: and nature doesn't want us to have exact copies of ourselves running around

Meredith: nature decided just 1 Elvis was enough ;)

drenken: haha

Meredith: so when we make kids our egg or sperm are made through a process that shuffles up and cuts down the amount of DNA we give our children

Meredith: our DNA gets shuffled up so that some of each of our chromosomes are given to each child (although not all)

Meredith: in a process called crossing over

Meredith: then our DNA gets cut in half

Meredith: and I do have a picture on that on

Meredith: one sec

Meredith: if you could get your movie playing ... can you see the board

Meredith: or no?

flickr2SL panel: Image from http://www.palaeos.com/Fungi/Lists/Glossary/Images/Meiosis.gif

drenken: I see it

Meredith: ok - great

Meredith: so here is cell division via meiosis for just one parent

Meredith: this cell starts with 4 chromosomes

Meredith: and each of the cells it makes (called gametes) gets how many?

Meredith: if you can see that

drenken: 2

Meredith: right

Meredith: those gametes are the egg or sperm, by the way

Meredith: and the initial cell is called a germ cell

Meredith: and here is why they number of chromosomes gets cut in half. .

flickr2SL panel: Image from http://www.lpch.org/photos/greystone/ei_0105.gif

Meredith: mom has DNA to give

Meredith: and dad has DNA to give

Meredith: so each give their kids 1/2 of the DNA

Meredith: since 1/2 + 1/2 = 1 normal set in the child after fertilization

Meredith: so mitosis keep chromosome number the same ... meiosis cuts chromosome number in half

drenken: ok I got it

Meredith: great

drenken: thanks

Meredith: any others from that quiz?

drenken: I think I’m good ... reading the general feedback helps out

Meredith: good

Meredith: then have a good night

Meredith: and ttyl

drenken: you too

Meredith: night!