Sex Determination | Genetics | Biology | FuseSchool


sex determination did you know that

nearly all tortoiseshell cats are female

we'll find out by later in this video we

are going to discover how sex is

determined human body cells have 46

chromosomes arranged in 23 pairs there

are 22 pairs of autosomes and one pair

of sex chromosomes or allo zones for a

male the sex chromosomes are usually XY

whilst for a female they are xx to make

a baby

a sperm has to join with an ovum or an

XL we looked at sperm and egg cells in

detail in this video you should know

that they only have half of the DNA of a

body cell they are haploid instead of 46

chromosomes so 23 pairs they just have

23 chromosomes in total 22 autosomes and

one sex chromosome or alisone an ovum

will always have an X chromosome but the

sperm will have an X or a Y if we looked

at this in a punnett square the gametes

from the female would always be X so X X

and the gametes from the male would be

either X or Y can you complete the

punnett square to show the probability

of having a male or a female child pause

the video complete the punnett square

and click Play when you're ready to

check did you get it right so the X from

the ovum and the X from the sperm would

produce a female baby and the X from the

ovum and the Y from the sperm would give

us a male child so really it is the man

who determines the gender of the child

he brings the Y which is the only chance

of a males child

unfortunately for an boylan a wife of

King Henry the 8th of England in the

16th century she was executed for not

providing a male heir to the throne

really he sperm were to blame from the

punnett square we would expect 50% of

the offspring to be male and 50% to be

female but the actual outcomes may be

different one couple could for example

end up with four goals discounting

social factors of such as sex selective

abortions at both the natural male to

female sex ratio for humans is about 105


to 100 females it is thought that this

is Nature's Way of overcoming the fact

that males have a higher risk of dying

younger than females the overall wold

male to female sex ratio drops down from

101 males - every 100 females so it is

closer to the expected 50% of each now

let's get back to our cat most

tortoiseshell cats are female because

this fur color is a characteristic found

on the X chromosome but males have One X

chromosome so why can't males be

tortoiseshell for a tortoiseshell cat

two X chromosomes are needed to show the

three different colors so as females

have X X 6 chromosomes they can be

tortoiseshell but X Y males can't now I

say most rather than all because you can

occasionally get a male tortoiseshell

cat just like you can occasionally get a

human man with X X chromosomes these

rare individuals have an extra strand of

DNA and so our X X Y rather than just X

Y so the male has the double X is needed

to be tortoiseshell there are other rare

chromosomal disorders that mean you can

have xx human males and ex-wife emails

or Turner syndrome when one sex

chromosome is present a solitary X XY Y

and double X double Y are two more

syndromes and they are many others from

this video you should know that females


X X sex chromosomes and males usually

have XY the father provides the Y

chromosome and so the chance of having a

male child Falls and his shoulders if

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