(6) It is now known that this test also has limitations, since other genes are also required for testis development and in addition, it has been reported that individuals with XX
sex chromosomes, and therefore no SRY gene, can have testes.
TABLE 4-1 Karyotypes and gonadal sexes of various anomalies in human sexual differentiation Autosomes
Sex Chromosomes Gonad Syndrome Name 44 X0 Ovaries Turner's 44 XX Ovaries Normal female 44 XXX Ovaries Superfemale 44 XY Testes Normal male 44 XXY Testes Klinfelter's 44 XYY Testes Supermale 66 XXX Ovaries Triploid (lethal) 66 XXY Testes Triploid (lethal) 44 [XX.sup.sxr] Testes Sex reversal (1) (1) In this case a small piece of the Y chromosome is translocated to an X chromosome.
A gradual process of recombination restriction in the evolutionary history of the
sex chromosomes in dioecious plants.
The
sex chromosomes cannot be distinguished by their differential pycnosis in somatic metaphases of males and females (Figs.
Gonadal sex is determined by the combination of
sex chromosomes, unlike sex determination in the red-eared slider turtle (15).
At first metaphase the
sex chromosomes form a trianglular figure, with the [X.sub.1] and [X.sub.2] centromeres pushing to the same pole and the Y to the opposite one.
Sex chromosomes are of two types called X (female) and Y (male).
Pholcus phalangioides (Fuesslin 1775) revealed 2n = 24 = 11II + [X.sub.1][X.sub.2] in males with metacentric autosomes and acrocentric
sex chromosomes (Rodriguez-Gil et al.
The South American rodent Akodon azarae has a proportion of fertile females with
sex chromosomes indistinguishable from the XY chromosomes of males, namely X[Y.sup.*] females (Bianchi and Contreras, 1967; Espinosa and Vitullo, 1996).
Like all other chromosomes, the X and Y
sex chromosomes consists of strands of DNA along which are sited genes -- regions of DNA that provide the coded instructions for making proteins.
They're called the
sex chromosomes and are markedly different from ordinary chromosomes.
Current thinking is that it may result from either
sex chromosome mosaicism, the mutation of a gene involved in sex determination, or abnormal chromosomal translocation of the
sex chromosomes.