Humans have 46 chromosomes, including 22 pairs of autosomes and one pair of sex chromosomes. Females have paired X chromosomes, males have X and Y chromosomes. X chromosome is longer and contains more genes than Y chromosome
Medaka fish has XY sex determination system with dominant male determining gene DMY. DMY gene was first discovered in fish, located on Y chromosome. DMY evolved from duplicated DMRT1 gene 10-18 million years ago. DMY expression occurs in male gonads during sex determination
System found in mammals, insects, snakes, fish, and some plants. Females have XX chromosomes, males have XY chromosomes. Y chromosome presence triggers male development in humans. Most species require at least one X chromosome for survival
System determines sex in birds, fish, crustaceans, insects, flatworms, reptiles, and plants. Females have two dissimilar ZW chromosomes, males have two similar ZZ chromosomes. Sex determined by ovum, unlike XY system where sperm determines sex. Z chromosome is larger and has more genes than X chromosome
Baby's sex is determined at fertilization by sperm and egg chromosomes. Eggs always have X chromosome, sperm can have X or Y. Only sperm determines baby's sex, not either parent. Up to 1 billion sperm released during ejaculation
Normal grey cockatiels have grey bodies with yellow heads and orange cheek circles. Females typically have tail markings, males don't. Males have more striking orange spots on yellow faces. Females have lighter orange spots on muted yellow or grey faces