Why does a Drosophila have only 4 linkage groups when 8 chromosomes are present?

From what I understand, all the genes present on one chromosome constitute one linkage group. Then, Drosophila should have 8 linkage groups. Does this mean we are counting only one linkage group from each pair of homologous chromosomes? If so, then why?

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1 Answer
Mandira P.
Jan 24, 2018

In diploid nucleus, each chromosome is represented twice: by homologous pair and there are same genes on homologous chromosomes.

Explanation:

In fruit fly, there are four pair of chromosomes: three are autosomal pairs and one pair of sex chromosomes. Genes present on one chromosome form a linkage group. Homologous chromosomes carry same set of genes (the alleles may differ), hence same linkage group.

![http://slideplayer.com/8572310/26/images/6/Drosophila+Chromosomesjpg](useruploads.socratic.org)

Please note, that there are not 4 but actually 5 linkage groups in Drosophila. This is because other than the three autosomes there are a pair of sex chromosomes which are not homologous, i.e. genes on X chromosome are not same as the genes on Y chromosome.

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