Understanding Genotype and Phenotype in Plants

The question asks us to determine the phenotype of a plant given its genotype as ttRr. To answer this, we need to understand how genotypes (the genetic makeup) translate into phenotypes (the observable characteristics) based on dominant and recessive alleles.

In many genetic traits, there are different versions of a gene called alleles. Some alleles are dominant, meaning that if they are present, their trait will be expressed in the phenotype. Other alleles are recessive, and their trait will only be expressed if two copies of the recessive allele are present (i.e., the genotype is homozygous recessive).

Analyzing the Given Genotype ttRr

The genotype ttRr describes two different traits:

• The alleles for the first trait are 'tt'.
• The alleles for the second trait are 'Rr'.

Let's analyze each pair of alleles separately to determine the phenotype for each trait.

Determining Phenotype for the 'tt' Genotype (Height)

The genotype for the first trait is 'tt'. Assuming that 'T' represents the allele for Tall height (dominant) and 't' represents the allele for dwarf height (recessive), we can determine the phenotype:

• A plant with genotype TT or Tt would have the Tall phenotype because the 'T' allele is dominant.
• A plant with genotype tt will have the Dwarf phenotype because both alleles are the recessive 't' allele.

Since the genotype is 'tt', the plant's height phenotype is Dwarf.

Determining Phenotype for the 'Rr' Genotype (Seed Shape)

The genotype for the second trait is 'Rr'. Assuming that 'R' represents the allele for Round seed shape (dominant) and 'r' represents the allele for wrinkled seed shape (recessive), we can determine the phenotype:

• A plant with genotype RR or Rr would have the Round phenotype because the 'R' allele is dominant.
• A plant with genotype rr will have the Wrinkled phenotype because both alleles are the recessive 'r' allele.

Since the genotype is 'Rr', the plant's seed shape phenotype is Round.

Combining Phenotypes for Genotype ttRr

By combining the phenotypes determined for each trait, we get the overall phenotype for a plant with genotype ttRr:

• Height phenotype from 'tt': Dwarf
• Seed shape phenotype from 'Rr': Round

Therefore, the phenotype of a plant with genotype ttRr is Dwarf and Round.

Comparing with Options

Let's compare our determined phenotype with the given options:

1. Dwarf and Round
2. Tall and Wrinkled
3. Dwarf and Wrinkled
4. Tall and Round

Our determined phenotype, Dwarf and Round, matches option 1.

In summary, the genotype ttRr results in the Dwarf height phenotype and the Round seed shape phenotype, leading to an overall phenotype of Dwarf and Round.

Revision Table: Genotype and Phenotype Analysis

Additional Information on Mendelian Genetics

This problem is an example of Mendelian genetics, specifically dealing with two traits inherited independently. This concept is described by Mendel's Law of Independent Assortment, which states that alleles of different genes assort independently of one another during gamete formation. In this case, the alleles for height (T/t) are inherited independently of the alleles for seed shape (R/r).

Understanding dominant and recessive alleles is fundamental to predicting phenotypes from genotypes. A dominant allele masks the effect of a recessive allele when present together in a heterozygous genotype. A recessive allele only expresses its trait in the phenotype when it is present in a homozygous recessive genotype.

For example, in the genotype Rr, the 'R' (Round) allele is dominant over the 'r' (wrinkled) allele, so the phenotype is Round. In the genotype tt, there is no dominant 'T' allele to mask the 't' (dwarf) allele, so the phenotype is Dwarf.