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  • Sex-linked Inheritance In Drosophila – Zoology Notes – For W.B.C.S. Examination.
    Posted on November 13th, 2019 in Zoology
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    Sex-linked Inheritance In Drosophila – Zoology Notes – For W.B.C.S. Examination.

    ড্রসোফিলায় যৌন লিঙ্কিত উত্তরাধিকার – প্রাণিবিদ্যা নোট – WBCS পরীক্ষা।

    The chromosomes present in the diploid cells of the majority of the sexually reproducing animals are of two types: autosomes bearing genes for somatic characters and sex chromosomes bearing genes for sex.Continue Reading Sex-linked Inheritance In Drosophila – Zoology Notes – For W.B.C.S. Examination.

    Sex chromosomes also carry some genes for non-sexual characters such as colour blindness and haemophilia.

    Such genes which are always associated with sex chromosomes are called sex-linked genes. In man and Drosophila the sex chromosomes (X and Y) are unequal in size and shape, X being larger and rod shaped whereas Y is small and slightly curved. In birds and butterflies the sex chromosomes (Z and W) are also unequal in shape and size, Z being larger than W.

    In Mendelian pattern of inheritance, the genes for contrasting characters were located on autosomes but not on the sex chromosomes. Secondly, the result of reciprocal cross is same as normal cross which is not the case with sex linked inheritance. There are three types of sex-linked genes depending upon their association with particular chromosome.

    They are as follows:

    (i) The genes which are located on X-chromosomes are called X-linked genes or sex linked genes.

    (ii) The genes which are located on Y chromosomes are called Y-linked genes or holandric genes.

    (iii) Certain genes are found to occur in both X and Y chromosomes. Such genes are called incomplete sex-linked genes.

    In order to understand the inheritance of character present in sex chromosomes, let us understand transmission of X-chromosome from male individual in Drosophila or in man. The X-chromosome from male individual will always pass to the daughter, while X-chromosomes from female individual will be distributed equally among the daughter and sons.

    A character from the father goes to the daughter (F1) and then from daughter to grandson in the next generation (F2). Such type of inheritance is also called as criss-cross inheritance. In this type of inheritance result of the reciprocal crosses are not identical as in case with Mendelian crosses.

    Sex-Linkage in Drosophila:

    T.H. Morgan (1910) for the first time discovered sex-linkage in Drosophila melanogaster. Morgan when experimenting noted the sudden appearance of one white-eyed male (mutant form) in the culture of normal red-eyed Drosophila. This white-eyed male was crossed with red eyed female. The F1 flies (both male and female) were all red-eyed indicating that white eye colour is recessive to the normal red eye colour.When these F1 flies were inter-crossed freely, the red-and white-eyed flies appeared in the ratio 3: 1 in the F2 generation. White- eyed flies were male. Among the red eyed flies two-third were female and one-third were male. The females were all red eyed whereas 50% males were white eyed and the remaining 50% males were red eyed .If a reciprocal cross is performed between white eyed female and red eyed male individual, all female individuals in Ft generation are red eyed and all male individuals, are white eyed. When these two types of individuals from F1 generation are inter crossed, female population in F2 generation will consist of 50% red eyed and 50% white eyed individuals. Similarly the male population in this generation consists of 50% red eyed and 50% white eyed individual.

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