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प्रश्न
Explain Mendel’s monohybrid progeny with the help of any one cross.
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उत्तर
- In this experiment, Mendel brought about the cross between two pea plants with only one pair of contrasting characters. This type of cross is called a monohybrid cross.
- Tall pea plants and dwarf pea plant were used in this cross. Hence, this is parent generation (P1). Mendel referred to the tall and dwarf plants as dominant and recessive respectively. The tall plant was referred to as dominant because all the plants in the next generation were tall.
- The dwarf plant was referred to as recessive because this characteristic did not appear in next generation at all.
- Though all the plants in F1 generation were tall, they contained the factor responsible for dwarfness. i.e. though the phenotype of F1 plants is tall, their genotype is mixed.
- Genotype of F1 tall plants is Tt and it produces two types of gametes, T and t. Thus, based on this, we can say that in case of tall plants of F1 and P1 generations, though they show similar phenotype, their genotypes are different. Mendel further continued this experiment and brought about self-fertilization in F1 plants from which a second filial (F2) generation was produced.
- According to the data collected by Mendel, out of 929 pea plants, 705 were tall and 224 were short. Thus, the phenotypic ratio of these plants is 3(tall):1(dwarf) and genotypic ratio is 1(TT):2(Tt):1(tt).
- Thus, it can be inferred that in the F2 generation, phenotypically there are two types of plants whereas genotypically there are three types. These types are shown in the following table.
F2 Pure dominant TT - tall plants Homozygous F2 Pure recessive (tt) - dwarf plants Homozygous F2 Hybrid plants (Tt) - tall plants Heterozygous
| Mendel’s experiment of the Monohybrid Cross | |||
| Parental Generation P1 | |||
| Phenotype | Tall | Dwarf | |
| Genotype | TT | tt | |
| Gametes | T | t | |
| First Filial Generation F1 | Tt | ||
| (Phenotype: Tall) | |||
| Parental Generation P2 | Selfing in F1 | ||
| Phenotype | Tall | Tall | |
| Genotype | Tt | Tt | |
| Gametes | T t | T t | |
| First Filial Generation F2 | Male gamete/Female gamete | T | T |
| T |
TT Tall |
Tt Tall |
|
| t |
Tt Tall |
tt Dwarf |
|
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संबंधित प्रश्न
A child has blood group O. If the father has blood group A and the mother has blood group B, work out the genotypes of the parents and the possible genotypes of the other offspring.
Given below are the F2 – phenotypic ratios of two independently carried monohybrid crosses :
(i) 1 : 2 : 1
(ii) 3 : 1
Mention what does each ratio suggest.
Mention whether the cross is a monohybrid or dihybrid.
What is a monohybrid cross? How did Mendel perform this cross?
Differentiate Between Monohybrid and Dihybrid cross.
Name the conditions when both the alleles are identical?
A garden pea plant produces axial white flowers. Another of the same species produced terminal violet flowers. Identify the dominant trait?
What do you understand by the terms phenotype and genotype?
Pure-bred tall pea plants are first crossed with pure-bred dwarf pea plants. The pea plants obtained in the F1 generation are then selfed to produce F2 generation of pea plants.
Which type of plants was missing in the F1 generation but reappeared in the F2 generation?
Differentiate between inherited and acquired characters. Give one example for each type.
Give reasons why acquired characters are not inherited.
Genotypic ratio of a monohybrid cross is ______.
When a tall plant with rounded seeds (TTRR) is grossed with a Dwarf plant with wrinkled seeds (ttrr) the F1 generation consists of tall plants with rounded seeds. How many types of gametes the F1 plant would produce?
In a monohybrid cross of plants with red and white flowered plants, Mendel got only red-flowered plants. On self-pollinating these F1 plants got both red and white flowered plants in 3:1 ratio. Explain the basis of using RR and rr symbols to represent the genotype of plants of parental generation.
In a plant tallness is dominant over dwarfness and red flower is dominant over white. Starting with the parents work out a dihybrid cross. What is standard dihybrid ratio? Do you think the values would deviate if the two genes in question are interacting with each other?
In a cross between red coloured and white coloured flowers, when plants with red coloured flowers of F1 generation were self pollinated, plants of F2 generation were obtained in which 75% of plants were with red flowers and 2.5% plants were with white flowers.
Explain the inheritance of traits in the above cross with the help of a flow chart only along with the ratio of plants obtained.
Assertion (A): In humans, if gene (B) is responsible for black eyes and gene (b) responsible for brown eyes, then the colour of eyes of the progeny having gene combination Bb, bb or BB will be black only.
Reason (R): The black colour of the eyes is a dominant trait.
