Which processes lead to most genetic variation in sexually reproducing organisms

Which processes lead to most genetic variation in sexually reproducing organisms

A: Independent assortment of chromosomes in Meiosis.

B: Crossing over.

C: Random fertilization.

D: A, B, and C are correct.

Answer:

 The correct answer is option D. Options A, B and C all are true.

Explanation:

The processes which lead to genetic variation in sexually reproducing organisms include; a) Independent assortment of chromosomes in Meiosis, b) crossing over, and c) random fertilization.

Which processes lead to most genetic variation in sexually reproducing organisms

Let’s first discuss “what is genetic variation?” before mentioning the processes which introduce the genetic variation.

Genetic Variation:

Genetic variation is the process which has a crucial role in the process of natural selection by enabling the best individuals to reproduce and survive.

Genetic variation occurs in the processes of crossing over and independent assortment during the phase of Meiosis in the gametes or sex cells.

A: INDEPENDENT ASSORTMENT OF CHROMOSOMES IN MEIOSIS:

Independent Assortment shows how different genes separate from one another independently when reproductive cells develop. This independent assortment of genes occurs during Meiosis.

Meiosis:

Meiosis is the process of cell division that happens in the gametes or sex cells during sexual reproduction. Meiosis ensures the introduction of genetic variation.

In Meiosis, the cell divides twice in such a way that four cells are formed from one parent cell. The chromosomes also exchange their genetic material in crossing over.

As the chromosomes vary from one other so, they randomly line up in the cell. It is called independent assortment.

B: CROSSING OVER:

The process in which the chromosomes exchange their genetic material is called crossing over.

Crossing over occurs during “Prophase I,” which is the first stage of Meiosis. During this stage, the homologous chromosomes pair up.

When homologous chromosomes exchange segments with each other, it switches the pieces of DNA as (Chromosomes contain genes in the form of DNA sequences); thus, variation occurs.

During the process of crossing over the chromosomes break as well as rejoin at the same place.

C: RANDOM FERTILIZATION:

Random fertilization is another process that leads to Genetic Variation. Thus, sexual reproduction ensures that genetic variation happens during cell division and fertilization.

During Meiosis I, there are two ways each homologous pairs of chromosomes can line up ( I I’ ) & ( I’ I ) – we can calculate the possible number of random combinations of chromosomes in each gamete (ie. sperm/egg) using the equation:

number of possible combinations = 2n
where n is the number of chromosomes in the system.
Humans have 23 chromosomes so this gives rise to 8,388,608 genetically unique gametes through independent assortment alone

Random fertilization refers to the fact that if two individuals mate, and each is capable of producing over 8million potential gametes, the random chance of any one sperm and egg coming together is a product of these two probabilities – some 70 trillion different combinations of chromosomes in a potential offspring.
think about that for a second

Crossing over occurs during tetrad formation of Metaphase I of meiosis; when portions of the homologous pairs get exchanged, it results in the sister chromatids involved being recombined and genetically distinct from the other sister chromatid – this can happen more than once and can happen at random loci (locations) on the chromosome.

Because crossing over can give rise to an additional unique combination of alleles, each occurrence would effectively double the number of genetically unique gametes – and because crossovers occur randomly this means that number earlier (70 trillion) doesn’t even begin to describe the potential variation in offspring that can exist given the three concepts listed.