sex chromosome |
Either of a pair of chromosomes, usually called X and Y, that in combination determine the sex of an individual in many animals and in some plants. In mammals, XX results in a female and XY in a male, while the opposite is true in birds (where the designations ZW for female and ZZ for male are often used). Sex chromosomes carry the genes that control the development of reproductive organs and secondary sex characteristics. In some organisms, sex is determined by environmental influences. See also X-chromosome, Y-chromosome.