4 public questions tagged with this topic.
A normal human male has 46 chromosomes, including one X and one Y sex chromosome.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles
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
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
Human-mouse somatic hybrids preferentially lose human chromosomes because mouse spindle apparatus cannot stably maintain human centromeres leading to gradual elimination during successive divisions whereas mouse chromosomes segregate faithfully due to compatibility with cellular machinery. Initial fusion product contains tetraploid genome complement then human chromosomes shed randomly. Resulting clones retain one to few human chromosomes ideal for correlation mapping of genes to chromosomes. Hybrids with plant or yeast partners incompatible and nonviable making mouse partner standard for human mapping through chromosome loss phenomenon.
Ref: Hartl & Ruvolo, Genetics, 6th ed., Chapter 5: Human Chromosome Loss in Mouse Hybrids Preferential Elimination
