Genes follow inheritance patterns such as autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. These patterns dictate how traits are passed from one generation to the next.
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. a. What will be set of genes present in the F1 generation? B. Give reason why only tall plants are observed in F1 progeny c. 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 F 2 generation.
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a. Genes present in the F1 generation:
In the given cross, tall pea plants (TT) were crossed with short pea plants (tt). The F1 generation will have the genotype Tt. Each pea plant in the F1 generation inherits one allele from each parent, and since the tall trait is dominant (T), the presence of at least one dominant allele (T) results in a tall phenotype. Therefore, the set of genes present in the F1 generation is Tt.
b. Reason for only tall plants in F1 progeny:
In Mendelian genetics, when a dominant allele is present, it masks the effect of the recessive allele. In this case, “T” is the allele for tallness (dominant), and “t” is the allele for shortness (recessive). The genotype of the F1 plants is Tt, where the dominant allele “T” determines the tall phenotype. The presence of even one dominant allele results in the expression of the dominant trait, so all plants in the F1 generation appear tall.
c. Genotype and phenotype of the F2 generation:
When the F1 plants (Tt) are self-pollinated, the possible combinations of alleles during gamete formation can lead to different genotypes in the F2 generation. The possible genotypes and phenotypes, along with their ratios, can be determined using a Punnett square or the multiplication rule.
The possible genotypes in the F2 generation are:
• TT (tall)
• Tt (tall)
• Tt (tall)
• tt (short)
The expected phenotypic ratio in the F2 generation is 1:2:1 for tall:tall:short.
Now, if a total of 800 plants are produced in the F2 generation, you can calculate the expected number of plants for each phenotype:
Calculation Diagram:
Therefore, in the F2 generation, you would expect 600 tall plants, 200 short plants, and no medium-height plants. The genotype of the tall plants could be either TT or Tt.
a. Tt
b. Traits like ‘T’ are called dominant traits, while those that behave like ‘t’ are called recessive traits. /Alternatively accept the definition of dominant and recessive traits with examples of T and t respectively /Alternatively accept the law of Dominance with examples of T and t.
c. Out of 800 plants 600 plants will be tall and 200 plants will be small, 1 TT: 2Tt: 1tt.