Sexual reproduction involves the combination of genetic material from two organisms to create a new organism. It occurs in eukaryotic organisms through processes like meiosis and fertilization. Meiosis involves the halving of chromosomes, while fertilization involves the fusion of two gametes and restoration of the original chromosome number. Evolutionary theories propose that sexual reproduction developed and is maintained because it allows for increased genetic variation through recombination and adaptation to changing environments.

1. Sexual reproduction
Sexual reproduction is a process that creates a new organism by combining the genetic material of two organisms. It
occurs in eukaryotes.[1][2] Prokaryotes display processes similar to sex (mechanisms for lateral gene transfer such
as conjugation, transformation and transduction), but they do not lead to reproduction. Prokaryotes reproduce
throughasexual reproduction. In multicellular eukaryote organisms, an individual is created anew; in prokaryotes, the initial
cell has additional or transformed genetic material. In a process called genetic recombination, genetic material (DNA)
originating from two different individuals join up so that homologous sequences are aligned with each other, and this is
followed by exchange of genetic information. After the new recombinant chromosome is formed, it is passed on to progeny.
some of these models remain controversial. New models presented in recent years, however, suggest a basic
advantage for sexual reproduction in slowly reproducing, complex organisms, exhibiting characteristics that
depend on the specific environment that the given species inhabit, and the particular survival strategies that
they employ.[8] Sexual reproduction is the primary method of reproduction for the vast majority of
macroscopic organisms, including almost all animals and plants. The evolution of sexual reproduction is a major
puzzle. The first fossilized evidence of sexual reproduction in eukaryotes is from the Stenian period, about 1 to
1.2 billion years ago.[3] There are two main processes during sexual reproduction in eukaryotes: meiosis,
involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and
the restoration of the original number of chromosomes. During meiosis, the chromosomes of each pair
usually exchange genetic information to achieve homologous recombination. Evolutionary thought proposes several
explanations for why sexual reproduction developed and why it is maintained. These reasons include fighting
the accumulation of deleterious mutations, increasing rate of adaptation to changing environments[4] (see
the red queen hypothesis), dealing with competition (see the tangled bank hypothesis) or as an adaptation for
repairing DNA damage and masking deleterious mutations.[5][6][7] The maintenance of sexual reproduction has
been explained by theories that work at severallevels of selection, though some of these models remain
controversial. New models presented in recent years, however, suggest a basic advantage for sexual
reproduction in slowly reproducing, complex organisms, exhibiting characteristics that depend on the specific
environment that the given species inhabit, and the particular survival strategies that they employ.[8]

2. ANN LORRAINE I. DELA CRUZ
IV-SSC
MS. DAISY P. NIME

4. STARFISH