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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
Give Technical Term:
The ratio of offspring on F2 generation in a dihybrid cross.
Multiple Choice Question
When two individuals differing in at least one character are crossed, the process is known as:
The physical expression of a gene is called ______.
Select the correct statement from the ones given below with respect to dihydrid cross
A cross between two tall plants resulted in offspring having few dwarf plants. What would be the genotypes of both the parents?
In a dihybrid cross, F2 phenotypic ratio is 13 : 3. It is case of ______.
Assertion: When the two genes in a dihybrid cross are situated on the same chromosome, the proportion of parental gene combinations is much higher than the nonparental type.
Reason: Higher parental gene combinations can be attributed to crossing over between two genes.
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.
Give a reason why only tall plants are observed in F1 progeny.
Mendel's law of independent assortment is based on F2 ratio of:
