Sexual reproduction is a kind of life cycle where generations alternate between cells with a single set of chromosomes haploid and cells with a double set of chromosomes diploid. Diploid cells divide into haploid cells in a process called meiosis. Two haploid cells combine into one diploid cell in a process called fertilisation. Between fertilisation and meiosis there can be a large number of cell divisions without change of the number of chromosomes. Fertilization creates a single-celled zygote which includes genetic material from both gametes.
In a process called genetic recombinationgenetic material DNA joins up so that homologous chromosome sequences are aligned with each other, and this is followed by exchange of genetic
Two rounds of cell division then produce four daughter cells with half the number of chromosomes from each original parent cell, and the same number of chromosomes as both parents. For instance, in human reproduction each human cell contains 46 chromosomes in 23 pairs. Meiosis in the parents' gonads produce gamete cells which only contain 23 chromosomes each. When the gametes are combined via sexual intercourse to form a fertilized egg, the resulting child will have 23 chromosomes from each Sexual reproduction in bacteria diagram genetically recombined into 23 chromosome pairs or 46 total.
Cell division mitosis then initiates the development of a new individual organism in multicellular organisms including animals and plantsfor the vast majority of whom this is the primary method of reproduction. The evolution of sexual reproduction is a major puzzle because asexual reproduction should be able to outcompete it as every young organism created can bear its own young.
This implies that an asexual population has Sexual reproduction in bacteria diagram intrinsic capacity to grow more rapidly with each generation. One definite advantage of sexual reproduction is that it prevents the accumulation of genetic mutations. Sexual selection is a mode of natural selection in which some individuals out-reproduce others of a population because they are better at securing mates for sexual reproduction. Prokaryoteswhose initial cell has additional or transformed genetic material, reproduce through asexual reproduction but may, in lateral gene transferdisplay processes such as bacterial conjugationtransformation and transductionwhich are similar to sexual reproduction although they do not lead to reproduction.
The first fossilized evidence of sexual reproduction in eukaryotes is from the Stenian period, about 1 to 1. Biologists studying evolution propose several explanations for why sexual reproduction developed and why it is maintained. These reasons include reducing the likelihood of the accumulation of deleterious mutations, increasing rate of adaptation to changing environments dealing with competitionand masking deleterious mutations. Larger populations appear to respond more quickly to benefits obtained through sexual reproduction than do smaller population sizes.
Maintenance of sexual reproduction has been explained by theories that work at several levels of selectionthough some of these models remain controversial. Sexual reproduction allows these species to exhibit characteristics Sexual reproduction in bacteria diagram depend on the specific environment that they inhabit, and the particular survival strategies that they employ. In order to sexually reproduce, both males and females need to find a mate.
Generally in animals mate choice is made by females while males compete to be chosen. This can lead organisms to extreme efforts in order to reproduce, such as combat and display, or produce extreme features caused by a positive feedback known as a Fisherian runaway. Thus sexual reproduction, as a form of natural selectionhas an effect on evolution. Sexual dimorphism is where the basic phenotypic traits vary between males and females of the same species.
Dimorphism is found in both sex organs and in secondary sex characteristicsbody size, physical strength and morphology, biological ornamentationbehavior and other bodily traits. However, sexual selection is only implied over an extended period of time leading to sexual dimorphism.
Apart from some eusocial waspsorganisms which reproduce sexually have a 1: The English statistician and biologist Ronald Fisher outlined why this is so in what has come to be known as Fisher's principle.
Insect species make up more than two-thirds of all extant animal species. Most insect species reproduce sexually, though some species are facultatively parthenogenetic. Many insects species have sexual dimorphismwhile in others the sexes look nearly identical.
Typically they have two sexes with males producing spermatozoa and females ova. The ova develop into eggs that have a covering called the chorionwhich forms before internal fertilization. Insects have very diverse mating and reproductive strategies most often resulting in the male depositing spermatophore within the female, which she stores until she is ready for egg fertilization. After fertilization, and the formation of a zygote, and varying degrees of development, in many species the eggs are deposited outside the female; while in others, they develop further within the female and are born live.
There are three extant kinds of mammals: In placental mammals, offspring are born as juveniles: After several months or years, depending on the species, the sex organs develop further to maturity and the animal becomes sexually mature.
Most female mammals are only fertile during certain periods during their estrous cycle, at which point they are ready to mate. Individual male and female mammals meet and carry out copulation. The vast majority of fish species lay eggs that are then fertilized by Sexual reproduction in bacteria diagram male,  some species lay their eggs on a substrate like a rock or on plants, while others scatter their eggs and the eggs are fertilized as they drift Sexual reproduction in bacteria diagram sink in the water column.
Some fish species use internal fertilization and then disperse the developing eggs or give birth to live offspring. Fish that have live-bearing offspring include the guppy and mollies or Poecilia.
Fishes that give birth to live young can be ovoviviparouswhere the eggs are fertilized within the female and the eggs simply hatch within the female body, or in seahorsesthe male carries the developing young within a pouch, and gives birth to live young.
Some fish are hermaphroditeswhere a single fish is both male and female and can produce eggs and sperm.