Mendel's Law of Independent Assortment - 5th Semester (CBCS)

 Mendel's Law of Independent Assortment



Mendel's law of independent assortment is the outcomes of is hybrid cross. According to this law the segregation of two or more characters in the same hybrid is independent of each other. Thus any allele of one gene is equally likely to combine with any allele of the other gene and pass into the same gamete. Independent segregation of 2 genes produces four different types of gametes in equal proportion.A random  Union among these gametes give rise to 16 possible zygotes. These yieled a 9:3:3:1 phenotype ratio which is known as the typical dihybrid ratio. The principle of independent assortment is Mendel made a cross between pea plant having yellow cotyledon colour and round seed surface and plants having green cotyledon colour and rough or wrinkle seed surface. All the F1 hybrid of this cross were phenotype with yellow and round seed surface when this F1 hybrid self fertilized they produce 4 types of phenotypically different plans in the following ratio.

 

 

Mendel's dihybrid cross between pea plants with yellow round seed and green wrinkle seed has been explain with the help of the cross as follows. The homologous pea plant with yellow round seeds have the allele RRYY for yellow colour of seed or one member pair of homozygous chromosome and alleles RR for round shape of seed on the other member of a pair of homologous chromosome. Similarly green wrinkle seed have the allele yy for green colour of seed on one member of a pair of homologous chromosome and allele rr for wrinkle shape of seed on other member of the pair of homologous chromosome. During gametogenesis the homozygous plans having YYRR alleles produced gametes  with YP allele and the homozygous plants having YYRR allele produced gametes with yr allele respectively. After fertilization between this game it's a hybrid plan is produce with YyRr alleles showing complete dominance of Y & R alleles over y and r allelel respectively. In the sale of F1 hybrid or the one member of homologous pair of chromosome occur the alleles for yellow and green cotyledon colour and on the other member of a pair of homologous chromosomes are the alleles for round and wrinkle seed shape. in F1 hybrid with YYRR alleles during gametogenesis produced four types of gametes with the following composition.


Mandel's Dihybrid Cross Table

    These 4types of gametes i.e. YR,Yr,yR&yr of F1 hybrids unit randomly in the process of fertilization & produced 16 type of individuals in F2 generation in the ratio of 9:3:3:1. Then results hv prove the law of independent assortment & show that each pair of contrasting characters behaves independently & bears no parmanent association with allele R in parent but it doesn't always remain associated with allele R in the hybrids. It also remains associated with allele r.

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