Triploid (3n) watermelons, which are seedless, are produced by crossing a tetraploid (4n) strain with a diploid (2n) plant. Explain why this mating produces a triploid individual.

Verified step by step guidance

1. Step 1: Understand the terms. In this context, 'diploid' refers to a cell or organism that has two sets of chromosomes, 'tetraploid' refers to a cell or organism that has four sets of chromosomes, and 'triploid' refers to a cell or organism that has three sets of chromosomes.
2. Step 2: Understand the process of fertilization. In normal sexual reproduction, a diploid organism produces haploid gametes (with one set of chromosomes) through a process called meiosis. These haploid gametes then combine during fertilization to form a diploid zygote.
3. Step 3: Apply this understanding to the given problem. In this case, a tetraploid watermelon plant (with four sets of chromosomes) will produce gametes with two sets of chromosomes. A diploid watermelon plant (with two sets of chromosomes) will produce gametes with one set of chromosomes.
4. Step 4: Understand the result of the cross. When a gamete from the tetraploid plant (2n) fertilizes a gamete from the diploid plant (1n), the resulting zygote will have three sets of chromosomes, making it a triploid (3n) watermelon plant.
5. Step 5: Understand the significance. Triploid plants are often sterile because they cannot form normal gametes due to the uneven number of chromosome sets. This is why triploid watermelons are seedless.

Key Concepts

Polyploidy

Polyploidy refers to the condition of having more than two complete sets of chromosomes. In plants, polyploidy can lead to increased size and vigor, as well as the ability to produce seedless varieties. In the case of watermelons, tetraploid (4n) plants have four sets of chromosomes, which can be crossed with diploid (2n) plants to produce triploid (3n) offspring.

Chromosome Segregation

Chromosome segregation is the process during meiosis where homologous chromosomes are separated into different gametes. In the case of a tetraploid and a diploid cross, the tetraploid can produce gametes with either 2 or 1 set of chromosomes, while the diploid produces gametes with 1 set. When these gametes fuse, the resulting triploid individual has three sets of chromosomes, leading to the seedless trait.

Seedlessness in Triploids

Triploid organisms, such as seedless watermelons, are often sterile because they cannot undergo normal meiosis due to the uneven number of chromosome sets. This results in the inability to produce viable gametes, leading to the absence of seeds. The triploid condition is desirable in watermelons as it results in a fruit that is more appealing to consumers, who prefer seedless varieties.