Problem 13 - Campbell Biology

Question

A female Komodo dragon (Varanus komodoensis) kept in isolation in a zoo had offspring. 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

Genetic variation among the offspring is due to meiotic recombination occurring during parthenogenesis despite there being only one parent.

Step 1: Understanding Parthenogenesis

Parthenogenesis is a form of asexual reproduction where an egg develops into an organism without fertilization. This method can result in offspring that have two identical sets of chromosomes from the mother.

Step 2: Identifying Key Observations

Note that the offspring each have two identical copies of every gene, but they are not identical to each other. This implies genetic variation despite the absence of a second parent.

Step 3: Considering Meiosis

In typical sexual reproduction, meiosis involves recombination and segregation of chromosomes, leading to genetic diversity. In parthenogenesis, meiosis can still occur, which can introduce genetic recombination within the single parent’s genome.

Step 4: Exploring Genetic Recombination

Even in asexual reproduction via parthenogenesis, genetic recombination can take place during meiosis. This means the offspring can have different genetic combinations of the alleles present in the mother.

Step 5: Formulating the Hypothesis

The hypothesis is that the female Komodo dragon's offspring showed genetic variation due to meiotic recombination. Although the offspring originated from a single individual, the recombination of alleles during meiosis caused genetic variation among them.

Key Concepts

asexual reproduction

Asexual reproduction is a fascinating process where an organism creates offspring without the fusion of gametes. This means there is no need for a mate.
Many creatures use this method, including certain plants, insects, and even some reptiles like Komodo dragons. Since no sperm is involved, the offspring receive all their genetic material from just one parent.
This is different from sexual reproduction, which combines genes from two parents to produce genetic diversity in offspring. While asexual reproduction generally involves less genetic variation, processes like parthenogenesis can still introduce some differences among the offspring.
This is primarily due to the genetic recombination that happens during meiosis.

genetic recombination

Genetic recombination is crucial for creating diversity among organisms, even in asexual reproduction.
During meiosis, which is a type of cell division, genes can be shuffled and recombined in new ways. This means that even if offspring are produced from a single parent, there can still be a mix of genetic traits passed on differently to each offspring.
In the case of the Komodo dragon, genetic recombination happens when different alleles (forms of a gene) from the mother are mixed and matched during meiosis. This mixing allows for unique genetic combinations in each offspring, explaining why they are not identical to each other.
Recombining genes is crucial for evolution, offering a way for species to adapt to changing environments.

meiosis

Meiosis is a type of cell division that reduces the number of chromosomes by half. It is essential for sexual reproduction but also plays a role in some types of asexual reproduction, like parthenogenesis.
In meiosis, a single cell divides twice to produce four cells, each with half the original number of chromosomes. During these divisions, chromosomes can exchange segments in a process known as crossing over. This exchange leads to genetic recombination.
Even without fertilization, as seen in the Komodo dragon, meiosis can introduce genetic variation. This is because the various segments of chromosomes can be rearranged and recombined in multiple ways, creating different genetic outcomes in each offspring.
Therefore, meiosis is not just a system for producing gametes but also a mechanism for enhancing genetic diversity.

genetic variation

Genetic variation is the diversity of genetic traits within a population. It is vital for the survival and adaptation of species.
In sexual reproduction, this variation comes from combining genes from two parents. However, asexual reproduction like parthenogenesis can also generate genetic diversity, thanks to processes like meiosis and genetic recombination.
In the Komodo dragon scenario, genetic variation is achieved through meiotic recombination. Each offspring receives a unique combination of genetic material from their single parent. This variation allows the offspring to differ from each other while still originating from one individual.
Such genetic diversity is crucial for evolution as it provides the raw material upon which natural selection can act.