A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers. but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as (a) TTWW (b) TTww (c) THW (d) TtWw

In Mendelian genetics, traits are controlled by genes, and genes come in different versions called alleles. Alleles can be dominant or recessive.

Dominant alleles are represented by uppercase letters (e.g., T for tallness, W for violet flowers). They mask the expression of recessive alleles. This means if an organism has at least one dominant allele, the dominant trait will be visible.

Recessive alleles, on the other hand, are represented by lowercase letters (e.g., t for shortness, w for white flowers). These traits only appear if the organism has two copies of the recessive allele. For instance, a plant will only be short if it has the combination tt.

In the described experiment, violet flowers (W) dominate white flowers (w). Therefore, all progeny have violet flowers, even though some parental genes may carry the recessive allele for white flowers.

Genotype refers to the genetic makeup of an organism—the combination of alleles they carry. Phenotype is the observable trait or characteristic resulting from the genotype.

For example, consider the genotype TtWw in the given exercise. 'Tt' consists of one dominant tall allele (T) and one recessive short allele (t). 'Ww' includes one dominant violet flower allele (W) and one recessive white flower allele (w).

Applying these terms to the experiment:

• The tall parent plant's genotype is TtWw.
• The short parent plant's genotype would be ttww (homozygous recessive for both traits).

Because the experiment reveals a mix of tall and short plants (phenotypes) in the progeny, we understand that the genotype of the tall parent must include both tall (T) and short (t) alleles.

The terms heterozygous and homozygous pertain to the allelic composition of genes.

An organism is homozygous for a trait if it has two identical alleles. This can be homozygous dominant (TT or WW) or homozygous recessive (tt or ww). Homozygous organisms consistently pass down one type of allele to their offspring.

An organism is heterozygous for a trait if it has two different alleles (Tt or Ww). Heterozygous organisms can pass down either allele, resulting in more genetic variation in the offspring.

In the described experiment:

• The tall parent plant (TtWw) is heterozygous for both height and flower color.
• The short parent plant (ttww) is homozygous recessive for both traits.

The presence of various phenotypes (tall and short plants with violet flowers) in the progeny can be explained by the heterozygous nature of the tall parent's genotype. This genetic diversity aids in understanding Mendel's laws of inheritance.