Types of sex determination — lesson. Science State Board, Class 10.

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\(XX-XO\) type:

Males have only one sex chromosome in this type of sex determination. Males are heterogametic, which means that some sperms carry the \(X\) chromosome while others do not. Females are homogametic \(XX\). Eggs fertilised by sperms with an \(X\) chromosome become females, 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.

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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.

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Sex determination in butterfly

Important!

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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2. Types of sex determination

Theory: