Meiosis | Genetics | Biology | FuseSchool

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sperm meets egg which then under go

multiple cell divisions to make a living

organism with trillions of cells all

doing their own specialized function

impressive but where do the egg and

sperm come from the answer is as you may

have guessed from the title

meiosis first it's good to know that

there are two types of cell division

processes

the simpler one is mitosis which

produces two identical cells with

exactly the same genetic

information you can think of them as

clones of each other and to find out

more why not look at our videos about

mitosis the other process is meiosis is

a much more complicated process creating

not two but four cells with only half

the number of chromosomes and crucially

all genetically different from each

other

both mitosis and meiosis include the

same phases prophase metaphase anaphase

and

telophase except in meiosis they happen

twice so they usually referred to as one

and

two the easiest way to remember these

phases names is to remember

itmat so let's look at meiosis in more

detail as always cellular division

starts with a process called DNA

replication this involves making two

identical copies of the original DNA

molecule the cell ends up temporarily

with double the normal number of

chromosomes you can learn more about DNA

replication in this

video in prophase 1 the duplicated

chromosomes join up with the pay from

the other parent so the mother's pay

bind with the father's P forming a group

of two chromosomes called holus

chromosomes what happens next is vital

for successful meiosis as each

chromosome is lined up next to its

partner pair one chromatid from each

side gets entangled with a corresponding

chromatid from the other side this is

called crossing

over during this brief period the two

chromatids swap certain sections of

DNA this is called

recombination the sections that they

trade correspond to the same location so

that each chromatid retains the correct

number of

genes recombination is really important

because it creates variety the new cells

aren't identical to the other parents

and they also are different to one

another as well they are new genetic

combinations in fact that's the whole

point of sexual

reproduction it increases genetic

variability each chromatid is now

different and as each one will end up in

a separate gamet it means each sex cell

is genetically different from all others

this explains why brothers and sisters

are different despite having the same

appearance only identical twins have the

same genetic makeup as they both

originate from the exact same egg and

sperm now back to meiosis next comes

metaphase

1 as the chromosones Align themselves up

in the middle of the

cell and in N phase one the spindle

fibers pull the chromosomes apart to

opposite ends in j telep phasee 1 and

cyto

Kinesis the cell pinches apart in the

middle and the nuclear membrane reforms

around the two new torto

cells that's the end of meiosis 1 now

for part two we start with our

recombined da cells each still with 46

chromosomes but sperm and egg cells only

have 23 chromosomes so we need to cut

these cells in

half here goes a second round of

division the proess is exactly the same

as before except that there is no DNA

replication we start straight with

prophase 2 with chromatin clumping again

to form

chromosomes then a line in the middle of

the cell during metaphase 2 and

chromatids are pulled apart during

anaphase 2 by the spindle

fibers telophase and cyto canesas pinch

the cells together with four new grand

cells being

formed the end of meiosis gives us four

different SE cells each each with only

23 chromosomes ready for future

fertilization but that's a story for

another

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