FERTILIZATION

STD-12      UNIT-6     CHA-3

HUMAN REPRODUCTION

FERTILIZATION

• Fusion of male gamete sperm with female gamete ovum to produce zygote is called as fertilization 
• Fusion of two haploid gametes sperm and ovum to produce diploid zygote is called as fertilization . 
• In human fertilization is internal i.e. completed in the ampulla of fallopian tube . 
• Process of fertilization in human is competed by following steps.
• Penetration of sperm in ovum . 
• Activation of ovum . 
• Fusion of male pronucleus with female pronucleus ovum . 
• Formation of zygote . 

Penetration of sperm In ovum : 

• More than hundred million of sperms discharged by male during sexual intercourse in vagina of female . 
• Thousands of sperms by their self movements transfer towards fallopian tube by the route of uterus . 
• hundreds of sperms reach in ampulla of fallopian tube and come in contact with ovum . 
• This occurs in ampulla of fallopian tube within 24 hours of ovulation because life of secondary oocyte after ovulation is 24 hours . 
• Sperm probably swim in female genital tract by means of lashing movements of tail of sperm . 
• As sperm come in contact with ovum agrosome release an enzyme hyaluronidase on egg membrane . 
• Egg membrane breaks and sperm head , neck and middle piece enters the ovum.
• For lashing movements of tail and penetration of sperm in ovum energy is supplied by mitochondria in middle piece of sperm.     
• Hyaluronidase enzyme dissolves the gelatinous glycoprotein layer around ovum zona pellucida and inner corona radiata.  
• Only one sperm penetrates into ovum 

Activation of ovum: 

• As sperm head neck and middle enters the ovum  become active 
• Path followed by a sperm to penetrates into ovum is called as penetration path. 
• Electrical changes in the surface of oocyte blocks the entry of other sperms to avoid polyspermy. 
• Zona pellucida gets retained immediately as the sperm enters the ovum to avoid polyspermy.  
• Thickness of zona pellucida goes on increasing to avoid polyspermy. 
• Size of sperm nucleus increases called as sperm pronucleus, also size of ovum nucleus increases called as ovum pronucleus. 
• Path fallowed by sperm pronucleus runs in ooplasm to reach to ovum pronucleus is called as fertilization path  

Fusion of sperm pronucleus and ovum pronucleus. 

• As sperm nucleus come in contact with ovum pronucleus, nuclear membranes of both pronuclei disappear.  
• Sperm pronucleus contains 23 chromosomes and ovum pronucleus contains 23 chromosomes because both are haploid in nature.  
• Due to this genetic materials from sperm pronucleus mixed with genetic materials of female pronucleus.  
• Due to this diploid condition is restored by the fusion or two haploid gamets in the process of fertilization.  
• Male pronucleus gets definite path to fuse with the female pronucleus by crossing 180 ° called as copulation path.  

Formation of zygote: 

• Zygote is a diploid cell or first cell of human body formed by the fusion of haploid male gamet sperm with haploid female gamet ovum.  
• Male gamet sperm shows haploid number of chromosomes in their nucleus and fernale gamet ovum also shows haploid number of chromosomes in their nucleus.  

Significance of Fertilization: 

• Fertilization restores diploid condition of zygote by fusion of two haploid gamete.  
• Due to mixing of genetic materials from two opposite gamets variations are formed in offsprings These variations are the raw materials of evolution.  
• Fertilization is an important step in the sexual reproduction in animals.  Sex of child is determined at the time of fertilization.  
• Fertilization stimulates zygote to undergo cleavage.

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