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प्रश्न
Describe the dihybrid cross upto F2 generation as conducted by Gregor Mendel using pure lines of Garden Pea for characters-seed shape and seed colour.
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उत्तर
Yellow colour was dominant over green and round shape was dominant over wrinkled. These results were identical to those that he got when he made separate monohybrid crosses between yellow and green-seeded plants and between round and wrinkled-seeded plants. Let us use the genotypic symbols Y for the dominant yellow seed colour and y for the recessive green seed colour, R for round-shaped seeds and r for wrinkled seed shape. The genotype of the parents can then be written as RRYY and rryy. The cross between the two plants can be written down showing the genotypes of the parent plants. The gametes RY and ry unite on fertilisation to produce the F1 hybrid RrYy. When Mendel self-hybridised the F1 plants, he found that 3/4th of F2 plants had yellow seeds and 1/4th had green. The yellow and green colours are segregated in a 3 : 1 ratio. Round and wrinkled seed shapes are also segregated in a 3 : 1 ratio; just like in a monohybrid cross. In the dihybrid cross Figure, the phenotypes round, yellow; wrinkled, yellow; round, green and wrinkled, green appeared in the ratio 9 : 3 : 3 : 1. Such a ratio was observed for several pairs of characters that Mendel studied. The ratio of 9 : 3 : 3 : 1 can be derived as a combination series of 3 yellow : 1 green, with 3 round : 1 wrinkled. This derivation can be written as follows: (3 Round : 1 Wrinkled) (3 Yellow : 1 Green) = 9 Round, Yellow : 3 Wrinkled, Yellow: 3 Round, Green : 1 Wrinkled, Green Based upon such observations on dihybrid crosses (crosses between plants differing in two traits) Mendel proposed a second set of generalisations that we call Mendel’s Law of Independent Assortment. The law states that ‘when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters’.
Phenotypic ratio:
| round yellow : round green : wrinkled yellow : wrinkled green |
| 9 3 3 1 |
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संबंधित प्रश्न
A homozygous Tall plant (T) bearing red coloured (R) flowers is crossed with a homozygous dwarf plant (t) bearing white flowers (r):
(1) Give the Genotype and Phenotype of the F2 generation.
(2) Give the possible combinations of the gametes that can be obtained from the F2 hybrid.
(3) Give the dihybrid ratio and the phenotype of the offsprings of the F2 generation when two plants of the F1 generation above are crossed.
Complete the following sentence with appropriate word:
A character that is suppressed is _________.
Under which conditions does the law of independent assortment hold good and why?
Define Genetics.
Two linked genes a and b show 20% recombination. The individuals of a dihybrid cross between ++ /++ × ab/ab shall show gametes ______.
A fruit fly exhibiting both male and female traits is ______.
How is the sex of a newborn determined in humans?
Sahil performed an experiment to study the inheritance pattern of genes. He crossed tall pea plants (TT) with short pea plants (tt) and obtained all tall plants in F1 generation.
When F1 plants were self-pollinated, a total of 800 plants were produced. How many of these would be tall, medium height or short plants? Give the genotype of F2 generation.
Independent assortment means:
