Problem 13 - Campbell Biology

Question

Synthesis/Evaluation SYNTHESIZE YOUR KNOWLEDGE A female Komodo dragon (Varanus komodoensis) kept in isolation in a zoo had progeny. Each of the offspring had two identical copies of every gene in its genome. However, the offspring were not identical to one another. Based on your understanding of parthenogenesis and meiosis, propose a hypothesis to explain these observations.

Step-by-Step Solution

Answer

During parthenogenesis in the Komodo dragon, meiotic chromosome duplication creates homozygous offspring, but genetic mutations generate individual differences.

Step 1: Review Parthenogenesis

Parthenogenesis is a form of reproduction where an egg develops into an organism without being fertilized by a male. Given that the Komodo dragon was kept in isolation, this is the likely method of reproduction.

Step 2: Understand Meiosis in Parthenogenesis

During meiosis in parthenogenesis, the egg undergoes duplication of its chromosomes automatically. This means each offspring has two identical copies of every gene (homozygous for all loci). This explains why the offspring have identical gene pairs.

Step 3: Identify Genetic Variation Sources

Despite being homozygous, genetic variation can still occur due to mutations during chromosome duplication or during the mitosis processes that follow. This is why the offspring are not identical to one another.

Step 4: Formulate Hypothesis

With understanding of parthenogenesis and meiosis, a plausible hypothesis is that the female Komodo dragon's offspring have two identical copies of every gene due to meiotic chromosome duplication but are not identical to one another due to genetic mutations.

Key Concepts

Parthenogenesis

Parthenogenesis is a fascinating form of asexual reproduction. Here, an egg develops into a new organism without the need for fertilization from a male.
This can occur in various animals like insects, amphibians, and reptiles.
In the case of the female Komodo dragon isolated in a zoo, parthenogenesis is the most plausible explanation for her ability to produce offspring in absence of a male.
This method bypasses the genetic mixing typically seen in sexual reproduction, leading to offspring that tend to have very similar genetic material to the mother.
Even though the offspring all had two identical copies of each gene, they were not identical to each other, which leads us to our next topics: meiosis and genetic variation.

Meiosis

Meiosis is a type of cell division unique to the production of gametes (egg and sperm cells). In parthenogenesis, meiosis is modified. Normally, meiosis involves two rounds of cell division that result in four daughter cells, each with half the number of chromosomes of the parent.
However, in parthenogenesis, the egg duplicates its chromosomes to ensure each offspring has a full set of chromosomes, making them homozygous for all loci (two identical copies of each gene).
This process explains why each offspring of the female Komodo dragon had two identical copies of every gene. But if meiosis is strictly accurate, why aren’t all the offspring identical?

Genetic Variation

Despite the identical genetic sets due to parthenogenesis, genetic variation can still arise. This is due to occasional mutations occurring during chromosome duplication or during subsequent mitotic divisions.
Mutations are random changes in the genetic code and can happen at any part of the genome, leading to differences among the offspring.
The mutations can change traits, resulting in offspring that are not identical to each other.
This explains why, even though the Komodo dragon's offspring had two identical copies of each gene, they still exhibited differences.
These genetic variations ensure some level of diversity and may provide some advantages in adapting to environmental changes.