sex chromosones

How many chromosomes do humans have?

46 chromosomes (23 pairs)

How many of the 46 chromosomes are autosomes?

44 chromosomes

What are the remaining two chromosomes called?

Sex chromosomes or gonosomes

What is another term for sex chromosomes?

Gonosomes or allosomes

What determines biological sex in humans?

The 23rd pair of chromosomes (sex chromosomes)

What sex chromosomes do females have?

Two X chromosomes (XX)

What sex chromosomes do males have?

One X and one Y chromosome (XY)

What triggers the development of testes during foetal development?

The presence of the Y chromosome

What happens if the testes do not develop during foetal development?

Ovaries develop instead

What is the probability of having a male or female baby?

50% chance of being male and 50% chance of being female

What are sex-linked genes?

Genes that are found only on the X chromosome and not the Y chromosome

Why do males and females have different chances of inheriting X-linked genes?

Males have only one X chromosome, while females have two

How are X-linked genes inherited in females?

Like autosomal genes—they can be dominant, recessive, incompletely dominant, or co-dominant

How are X-linked genes expressed in males?

Any X-linked gene is expressed because there is no second copy to mask it

Why do males often express recessive X-linked disorders?

Because they only have one X chromosome and no dominant allele to mask the recessive one

What must happen for a female to express a recessive X-linked disorder?

She must inherit two recessive alleles—one from each parent

What sex chromosomes would a biological male have?

XY

What sex chromosomes would a biological female have?

XX

If a male inherits a recessive X-linked disorder from his mother, will he express it?

Yes, because he has no second X chromosome to mask it

Can a female be a carrier of an X-linked disorder without showing symptoms?

Yes, if she has one recessive and one dominant allele

Why are X-linked disorders more common in males than females?

Because males only need one recessive allele to express the disorder

If a woman carries a recessive gene on one of her X chromosomes, what are the chances her son will inherit it?

50%

What does the Y chromosome do during development?

It triggers the formation of testes

Which chromosome is responsible for carrying more genes: X or Y?

X chromosome

Figure 1: Karyotype of males and females.

Figure 2: X and Y chromosomes.