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#linkage groups

3 public questions tagged with this topic.

Linkage and Mapping

Human males have how many linkage groups?

Human male karyotype 46,XY contains 22 autosome pairs plus X and Y which are largely nonhomologous aside small pseudoautosomal regions PAR1 PAR2 at tips. Genes outside PAR on X never recombine with Y genes, and Y genes unique to Y chromosome transmitted father to son. Thus X genes form one linkage group and Y genes form separate linkage group distinct from autosomes. Calculation 22 autosomes plus X plus Y equals 24 linkage groups. Exception demonstrates linkage group reflects distinct chromosome types rather than simple haploid number when heterogametic.

Ref: Hartl & Ruvolo, Genetics, 6th ed., Chapter 3: Heterogametic Sex and 24 Linkage Groups in Males

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Linkage and Mapping

Human females have how many linkage groups?

Human female karyotype 46,XX includes 22 autosome pairs plus homologous XX pair. Since X chromosomes share extensive homology and pair fully during meiosis, all X-linked genes belong to single linkage group inherited together. Adding 22 autosomal groups plus one X group totals 23 linkage groups. Number matches haploid set 23 where each autosome and X appears once in gamete. Females therefore represent standard situation where linkage group count equals haploid chromosome number without exception because sex chromosomes not heteromorphic, illustrating general rule clearly.

Ref: Pierce, Genetics: A Conceptual Approach, 7th ed., Chapter 5: Human Female Linkage Groups 23

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Linkage and Mapping

Number of linkage groups in an organism equals

Linkage group defined as set of genes whose loci reside on same physical chromosome and tend to be inherited together unless recombination separates them. Entire chromosome contains one linkage group because DNA molecule continuous and centromere ensures coordinated segregation. Counting distinct chromosomes in haploid complement therefore equals number linkage groups. Each linkage group corresponds to chromosome pair in diploid organism. Principle holds across species: Drosophila 2n=8 has 4 groups, pea 2n=14 has 7 groups, reflecting haploid number rather than gene number or allele diversity per locus.

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 4: Definition of Linkage Groups and Haploid Number

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