1. Sexual reproduction evolved around 1.2 million years ago and involves the combination of genetic material from two sexually differentiated organisms, usually male and female gametes. 2. Early organisms reproduced asexually through processes like binary fission and mitosis. Limited genetic recombination was possible in bacteria through conjugation and plasmid transfer. Eventually, haploid cells began fusing (syngamy) and meiosis evolved allowing for genetic mixing. 3. Specialized reproductive cells called gametes evolved, with motile sperm cells fertilizing stationary egg cells. This led to the development of separate gonads and coordinated mating behaviors involving simultaneous gamete release.

1. Origin of sexual reproduction
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2. Sexual reproduction
• Production of new individuals by combination of genetic
information from two sexually different organisms.
• In higher organisms male and female gametes are responsible
for it.
Example:
• Motile gamete, sperms
• Stationary gamete, eggs
According to gametes fusion
animals are of two basic types:
1. Isogamous: Gametes are not in distinct size and shape.
2. Anisogamous: Large (eggs) and small ( sperm) gametes
Anisogamy evolved from isogamy, evolution of large vs small
gametes.

3. History of sexual reproduction
Appears about 1.2 millions years ago
 Asexual means of reproduction
Early organisms reproduce asexually by so many types like,
Binary fission Mitosis
 Limited recombination in bacteria Recombination
Plasmid can be transfer in bacteria
during conjugation. Genetic
material transfer by the Sex Pilli.

4.  Syngamy
( Genetically dissimilar cell fusion) Syngamy
Two haploid cells fuse
completely. Simply known as
fusion of gametes. It is one
step meiosis.
 Meiosis (segregation and recombination) Meiosis
Endo mitosis was 1 step meiosis, after syngamy
two steps meiosis evolved.
 Matting types
Initially two matting types introduced,
i. Plus
ii. Minus

5.  Anisogamy
(sexual selection and gender differences)
It is basically origin of male and female sex.
It evolved from isogamy.
 Sex leads to evolution:
If we see the diversity around us, there are
myriad of sexual strategies ranging from
extremely simple to quit complex.
 It can be lined up to illuminate a smooth evolutionary process

7. SUMMERY
1. Start with single-sex (F), capable of cell fusion and meiosis
2. A second sex evolve. All combinations possible but MF work.
3. Simple multicellular organisms evolve. Sexual reproduction,
4. Specialized cells (gametes) for sexual reproduction.
5. Sperms use flagella for motility to find an egg.
6. Specialization leads to gonads for gametes production.
7. Coordinate mating behavior simultaneous release of gametes.
8. Internal fertilization develop in land habitual animals.
9. Male penetrate female, further facilitate internal fertilization.
10. Uterus evolve for better protect developing embryo.

8. References
i. Grassé, Pierre-Paul (1977), Evolution of Living Organisms (New York:
Academic Press).
ii. Mayr, Ernst (2001), What Evolution Is (New York: Basic Books).
iii. Ridley, Matt (1993), The Red Queen (London: Viking).
iv. Schecter, Julie (1984), “How Did Sex Come About?,” Bioscience, 34:680-
681, December.
v. www.nature.com%2Fscitable%2Ftopicpage%2Fsexual-reproduction-and-
the-evolution-of-sex-824
vi. www.youtube.com%2Fwatch%3Fv%3DwxysZmNsyDk%26feature%3Dshare