Types of sex determination — lesson. Science CBSE, Class 10.

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$XX-XO$ type:

Males have only in this type of sex determination. are heterogametic, which means that some carry the $X$ chromosome while others do not. Females are homogametic $XX$ . Eggs fertilised by sperms with an $X$ chromosome become , while eggs fertilised by sperms without an $X$ chromosome become males. Female is thus ( $2A$ + $XX$ ) and male is ( $2A$ + $XO$ ).

Some insects like grasshoppers, cockroaches and roundworms have the

$XX$ - $XO$ type of sex determination system.

Critique_of_the_Theory_of_Evolution_Fig_060.svg (1).png

Heredity of sex chromosomes in XO sex determination

$ZW$ -

$ZZ$ type:

In this type of sex determination, females are heterogametic, producing two types of gametes (

$Z$ and $W$ ), whereas males are homogametic, producing only one type of gametes (

$ZZ$ ). This type of sex determination can be observed in birds as well as some reptiles.

Sex determination in birds

$Z0$ -

$ZZ$ type:

Females have an odd sex chromosome (

$AA$ + $Z$ ) in the

$ZO$ - $ZZ$ type of sex determination, whereas males have two homomorphic sex chromosomes (

$AA$ + $ZZ$ ). This type of sex determination can be observed in butterflies and moths.

b-male-homogametic-and-female-heterogametic-sex-determination-l (1).jpg

Sex determination in butterfly

Important!

Do you know!
Organisms like wasps and bees have no sex chromosomes.

Reference:

https://www.genderinclusivebiology.com/newsletter/sex-determination-why-so-many-ways-of-doing-it

https://www.wikiwand.com/en/Sex-determination_system

https://www.slideserve.com/amos/factors-affecting-on-sex-reversal-of-fishes

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15. Types of sex determination

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