Question

________ contributes to variation in traits among the offspring of sexual reproducers. a. Crossing over c. Fertilization b. Random attachment d. both a and \(b\) \(\begin{array}{ll}\text { of chromosomes } & \text { e. all are factors }\end{array}\) to spindle poles

Short answer

The correct answer is e. all are factors.

Step-by-step solution

Analyze the Question

Identify what the question is asking. Here, it asks what contributes to variation in traits among the offspring of sexual reproducers. We need to know the processes involved in sexual reproduction that lead to genetic variation.

Understand the Concepts

Understand the processes involved: - Crossing over occurs during meiosis where homologous chromosomes exchange genetic material. - Random attachment of chromosomes to spindle poles influences the assortment of chromosomes. - Fertilization involves the random combination of gametes from each parent.

Evaluate Each Option

- Option a (Crossing over): Yes, it contributes to genetic variation by exchanging genetic material. - Option b (Random attachment of chromosomes to spindle poles): Yes, it contributes as it determines the distribution of chromosomes into gametes. - Option c (Fertilization): Yes, it contributes by combining genetic material from two parents randomly. - Option d (Both a and b): This option includes only two factors. - Option e (All are factors): This option considers all mentioned factors contributing to genetic variation.

Select the Most Comprehensive Answer

Among the given options, the one that covers all factors contributing to genetic variation is Option e: all are factors. This includes crossing over, random attachment of chromosomes, and fertilization.

Key concepts

Crossing Over

Crossing over is a remarkable process that adds to genetic variation during sexual reproduction. It happens in the first division of meiosis, a special type of cell division that results in gametes, such as sperm and egg cells, with half the chromosome number. During this process, homologous chromosomes, which are chromosome pairs of the same type from each parent, come together in close alignment.

At this stage, segments of DNA are swapped between these homologous chromosomes. This exchange occurs when the chromosomes form tight junctions called chiasmata.

• Crossing over shuffles genetic information, reshuffling genes in different ways.
• This process increases genetic diversity because it results in new combinations of genes that were not found in either parent.
• Each gamete receives a unique set of genes, which ultimately impacts the genetic traits seen in offspring.

Fertilization

Fertilization is a crucial part of sexual reproduction that facilitates genetic variation among offspring. This process occurs when two gametes, typically one from each parent, fuse together. The outcome is a zygote, which is the initial cell formed when a new organism is created.

One of the reasons fertilization is so significant in contributing to genetic variation is due to the random nature of gamete fusion.

• It's a chance event which sperm fertilizes which egg, introducing randomness in genetic combinations.
• The resulting zygote will have a mix of chromosomes from both parents, meaning that the offspring inherits a random combination of genetic materials.
• This variability is essential for the evolution of species because it forms the basis of different traits and adaptations.

Meiosis

Meiosis is a specialized type of cell division that produces gametes, such as sperm and egg cells. This process is fundamental to sexual reproduction as it reduces the chromosome number by half, ensuring that when fertilization occurs, the resulting offspring maintain the species-specific chromosome number.

Meiosis is characterized by two successive divisions:

• The first division (meiosis I) involves the separation of homologous chromosomes, leading to two cells with a unique combination of chromosomes.
• The second division (meiosis II) separates sister chromatids, similar to mitosis, and results in the formation of four genetically diverse gametes.

This diversity is due to two main phenomena:

• Independent assortment, where chromosomes are distributed randomly into gametes, leading to numerous possible genetic combinations.
• The previously mentioned crossing over, which further mixes genetic material between homologous chromosomes.

Together, these processes in meiosis underpin the genetic variation seen in sexually reproducing organisms.