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The ZW sex-determination system is a chromosomal system that determines the sex of offspring in birds, some fish and crustaceans such as the giant river prawn, some insects (including butterflies and moths), the schistosome family of flatworms, and some reptiles, e.g. majority of snakes, lacertid lizards and monitors, including Komodo dragons.
Some chromosomal sex determination systems in animals A sex-determination system is a biological system that determines the development of sexual characteristics in an organism . [ 1 ] Most organisms that create their offspring using sexual reproduction have two common sexes, males and females , and in other species, there are hermaphrodites ...
Each of these offspring contains numerous genes which have coding for specific tasks and properties. Males and females both contribute equally to the genotypes of their offspring, in which gametes fuse and form. An important aspect of the formation of the parent offspring is the chromosome, which is a structure of DNA which contains many genes. [1]
A large body of molecular evidence supports a variety of mechanisms for large evolutionary changes, including: genome and gene duplication, which facilitates rapid evolution by providing substantial quantities of genetic material under weak or no selective constraints; horizontal gene transfer, the process of transferring genetic material to ...
GCSE Bitesize was launched in January 1998, covering seven subjects. For each subject, a one- or two-hour long TV programme would be broadcast overnight in the BBC Learning Zone block, and supporting material was available in books and on the BBC website. At the time, only around 9% of UK households had access to the internet at home.
Human sexual reproduction, to produce offspring, begins with fertilization. Successful reproduction typically involves sexual intercourse between a healthy, sexually mature and fertile male and female. [1] During sexual intercourse, sperm cells are ejaculated into the vagina through the penis, resulting in fertilization of an ovum to form a ...
F1 hybrid (also known as filial 1 hybrid) is the first filial generation of offspring of distinctly different parental types. [1] F1 hybrids are used in genetics, and in selective breeding, where the term F1 crossbreed may be used. The term is sometimes written with a subscript, as F 1 hybrid.
XO sex determination can evolve from XY sex determination within about 2 million years. [clarification needed] It typically evolves due to Y-chromosome degeneration.As the Y-chromosome is not paired (though see pseudoautosomal region), it is susceptible to decay by Muller's ratchet.