Sexual reproduction is how most animals and plants reproduce.
Some protists and fungi also reproduce this way. Organisms that reproduce sexually have two different sexes: male and female.
In sexual reproduction, offspring are produced when sperms fertilise eggs from the female. Various steps are involved in this process.
The cells of an animal or higher plant have two sets of chromosomes: they are diploid. When gametes (sex cells) are produced, they have only one set of chromosomes: they are haploid. They have undergone a process of cell division called "reduction division" or meiosis. Two things happen during meiosis, each of which makes the offspring more variable. That means they are different from their parents and from each other.
Assortment is when the double set of chromosomes becomes a single set in each gamete. Of each pair of chromosomes, which one goes into a single gamete is random. Because the gene alleles on each chromosome are not always the same, this means that there is genetic variation between gametes. This process was Mendel's 'first law', the law of segregation.
Because crossing over occurs during meiosis, this increases the variety of the chromosomes. This makes recombination possible.
Assortment and crossing over make it certain that normally no two offspring of the same mother and father are identical. Identical twins are the exception. They are identical genetically because they developed from the same fertilised egg.
There are advantages and disadvantages of sexual reproduction, compared to asexual reproduction. The main issues are:
The origin of sexual reproduction is an advanced topic that cannot be dealt with here. A source that may help readers who are graduates in biological science may be helpful.
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