What is heterogametic ? Explain by giving proper examples ?
$=$ The chromosomal theory of sex determination was worked out by $E$.$B$. $Wilson$ and Stevens.
They named $XY$ chromosomes as allosome or sex chromosome and other chromosomes which have no relation with the sex and contain genes which determine the character as autosomes [$AA$]. Thus on the basis of the type of allosome present in the gamete, the parents can be of two types :
$(i)$ Homogametic i.e. Producing similar gametes.
$(ii)$ Heterogametic i.e. Producing different gametes.
These are various types of sex determination mechanism observed in various organisms as follow :
Mechanism of sex Determination
Male Heterogamety : The mechanism in which male produces two different types of gametes : $(i)$ Either with or without $X$-chromosome. $(ii)$Some gametes with $X$-chromosome and some without $Y$-chromosome.
$(i)$ $XX-\;XY$ Type : This type is present in certain insects like Drosophila melanogaster and mammals including human.
In males an $X$-chromosome is present but its other part is very small called as $ Y$-chromosome whereas females have a pair of only $X$-chromosome i.e. $\mathrm{XY}$.
Both males and females bear same number of chromosomes.
The males have autosomes plus $XY$-chromosomes and females have autosomes plus $XX$chromosomes.
The males produce two types of gametes containing $\mathrm{X}$ or $\mathrm{Y}$ sex chromosome and females produce only one type of gametes with an $X$-chromosome (homogametic).
Determination of sex in Drosophila : Thus in this type of sex determination the presence of Ychromosomes determines the maleness.
$(ii)$ $XX$-$XO$ Type : This type is present in a large number of insects, e.g., grasshopper etc.
Select the incorrect statement
Sex determination in Drosophila melanogaster is based on
Delete the odd one:
Match the items of column $I$ with column $II$
Column $I$ | Column $II$ |
$(a)\; XX-XO$ method of sex determination | $(i)$ Turner's syndrome |
$(b)\; XX-XY$ method of sex determination | $(ii)$ Female heterogametic |
$(c)$ Karyotype$-45 $ | $(iii)$ Grasshopper |
$(d)\; ZW-ZZ$ method of sex determination | $(iv)$ Female homogametic |
Select the correct option from the following
A woman has an $X$-linked condition on one of her $X$ chromosomes. This chromosomes can be inherited by