Explain the statements. i. Test cross is a back cross but back cross is not necessarily a test cross. ii. Law of dominance is not universally applicable. iii. Law of segregation is universally applicable.
Answers
Explanation:
i. Test cross is a back cross but back cross is not necessarily a test cross.
It is because; in back cross F1 generation can be crossed with either dominant or recessive parent. But in test cross, F1 generation is crossed with recessive parent only. Thus, test cross is a back cross but back cross is not necessarily a test cross.
ii. Law of dominance is not universally applicable.
In a cross between two organisms pure for any pair (or pairs) of contrasting characters, the character that appears in F1 generation is called dominant and the one which is suppressed is called recessive. In many cases, the dominance is not complete or absent. Phenomenon of dominance is significant as the harmful recessive traits are masked, i.e. not expressed in the presence of its normal dominant allele. e.g. In humans a form of idiocy, diabetes and haemophilia are recessive characters. Thus, law of dominance is significant and true, but it is not universally applicable.
iii. Law of segregation is universally applicable. Member of allelic pair in a hybrid remain together without mixing with each other and separate or segregate during gamete formation. Thus gametes receive only one of the two factors and are pure for a given trait. Therefore, this is also known as law of segregation. All sexually reproducing higher organisms are diploid (2n), i.e. with two sets of chromosomes and gametes are haploid (n), i.e. with one set of chromosome. Therefore, law of segregation is universally applicable.
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Explanation:
Mendel's studies yielded three "laws" of inheritance: the law of dominance, the law of segregation, and the law of independent assortment. Each of these can be understood through examining the process of meiosis.