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Hi friends, in this video let us understand what is the actual difference between law of
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independent assortment and law of segregation proposed by Grieker Mendel. For that let us
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consider this seed color and seed shape. As we know this yellow seed color is dominant over green
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and round seed shape is dominant over wrinkled. Let's begin with the monohybrid cross. So here
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the parental generation that is parent is homozygous capital Y capital Y yellow that is cross with
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homozygous, recessive, green, small y, small y. So it will be producing only one type of gamete
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So gamete, capital Y here, here it is small y and the F1 progeny or offspring is heterocygous
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capital Y and small y. Now we can understand what is actually segregation. So during the formation
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of gamete in this plant, what happens is this alleles segregate the capital Y and small y
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segregates and each moves into one gamete. So this gamete is having only capital Y and this gamete
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is having only small y. So there are two possible gametes that is capital Y and small y. This is
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called the law of segregation. During the gamete formation the allele segregate and each gamete
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is pure for an allele or each gamete can have only one allele now where both this capital y
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and small y together this gamete is an impossibility. Hope you are clear. Now what happens is in F2
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these are the gametes capital y small y if when it when this is selfed this is capital y small y
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we know that this becomes capital Y capital Y capital Y small y capital Y
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small y and small y small y so he got 3 is to 1 phenotypic ratio and 1 is to 2 is to 1 genotypic ratio suggesting that one character is dominant over other character The character that is expressed
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in F1 is called as a dominant character and the character that is masked in the F1 and reappeared
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in F2 is a recessive character. Here the yellow is a dominant character and green that is reappeared
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in F2 is the recessive character. Hope this much is clear. So this is the genotypic and phenotypic
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ratio. 3 to 1 phenotypic ratio and he found out that distinct traits were controlled by separate
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factors and he proposed that the law of segregation it states that two alleles that is capital Y and
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small y for each trait segregate or separate during the formation of gametes. So it separates
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so that each gamete has only one allele, never both. This gamete can have either Y or Y
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It cannot have Y and Y. This is called the law of segregation or law of separation of
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alleles during gamete formation. Hope you are clear. The next question he posed is are these
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traits inherited independently of one another. For that he conducted the next experiment
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Before this experiment he was an excellent mathematician also. By probability he found
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out that if this is independently assorting this will happen. Let us see. The phenotypic ratio
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in the case of monohybrid cross is three is to one. So this is the phenotypic ratio whereas round
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seed and trinkled seed it is also 3 is to 1. He used the product rule. The probability of two or more
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independent events occurring is a product obtained by multiplying the probabilities of individual events Multiply the individual phenotypic probability Let us see
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Suppose first case LO round the probability of appearing LO round if it is if these two traits are
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independently segregating is 3 by 4 into 3 by 4 that is here LO is 3 by 4 round is also 3 by 4 so that will be 3 into 3 9 by 16
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The probability of forming getting LO round is 9 by 16. LO wrinkled LO is 3 by 4 as you see this
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is 3 by 4 whereas wrinkled is 1 by 4 so it will be 3 into 1 3 by 16. LO wrinkled the number of
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progenies the ratio will be 3 by 16. Then green round, green is 1 by 4 so 1 by 4 into green round
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is 3 by 4. 3 by 4 that will be 3 by 16 and green wrinkled both are received 1 by 4 into 1 by 4
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so that will be 1 by 16. After dihybrid cross if you are getting this ratio mental confirm that
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both these traits are independently assorting. Then he conducted the experiment that is the
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dihybrid grows using two distinct traits. Let us take the same traits here capital Y capital Y
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capital R capital R small y small y small r small r yellow round and yellow wrinkled. So the gametes
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are capital Y capital R small y small r. So in the first generation it becomes capital Y capital
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small y capital R small r so what happens is during chemite formation each combinations all the possible combinations are formed in equal percentage Y R y r y r y r y r y r All these possible combinations are formed in equal percentage
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He did the dihybrid cross and he got 9 out of 16 the parental types in the ratio
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then as expected green round and yellow ringled the recombinant ones and 1 by 16 that is a recessive
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one that is a parental recessive. So as expected as predicted he got the 9 is to 3 is to 3 is to 1
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ratio. From this he proposed that states that genes do not influence each other with regard
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to the sorting of alleles into gametes. These two traits the color and the shape of the seed both are
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independently assorting and one is not influencing the other. Or every possible combination of
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alleles for every gene that is equally likely to occur. He got all possible combination of
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phenotypes. This is how Mendel proposed the law of independent assortment. Let me summarize
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Law of segregation states that during the formation of gametes, the alleles separate
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so that each gamete can have only one allele never both. Whereas law of independent assortments
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states that the genes do not influence each other with regard to the sorting of alleles into
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gametes. Distinct traits are independently assorting forming all possible combinations of phenotypes. There are exceptions in the case of linked genes or genetic linkage we have given
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a video on that based on Morgan's experiment. You can refer that. Also, the link is here
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Take care. Stay blessed. Thank you so much. You are with biology exams for it dot com
