How does sexual reproduction increase genetic variation?

Question

How does sexual reproduction increase genetic variation?

Answer 1

It increases genetic variation because of two main reasons.

The first reason is that it combines two different sets of genes, into a similar yet different genetic code.

The second reason is that mistakes, or mutations, almost always occur at a small level. These mutations change the genetic code slowly, but over time it is these mutations that are responsible for Natural Selection and Evolution as well.

Answer 2

It is because parents(which have different gene combinations) form new combinations to form new offsprings. Another reason is low level of mutation

Answer 3

First of all the process of Meiosis in the development of gametes for sexual reproduction inceases variation by producing genetically non identical gametes.

Sexual reproduction occurs by random fusion of gametes also increasing variation.

Meiosis is a type of division to produce haploid gametes for sexual reproduction and takes place in the seminifrous tubules in the testes of male (humans) and in the ovaries of females. In plants the male s*x cell (pollen) is produced in the anthers and the female s*x cells (ovules) takes place in the ovary.

Meiosis I halves the number or chromosomes. (a reduction division)

Meiosis II doubles the number of cells to give four haploid gametes.

The stages are Interphase, Prophase, Metaphase, Anaphase and Telophase.

Interphase only takes place once before Meiosis I, the other stages are repeated in Meiosis II.

Interphase : DNA replicates so that each chromosome consists of two identical chromatids joined at a centromere.

Prophase I : Nuclear membrane disappears and the chromosomes shorten and thicken and can now be seen under a light michroscope.Homologous chromosomes (one paternal and one maternal) line up side by side. Adjacent

chromatids can cross over at points called chiasmata and exchange genetic material (Increased variation).

Metaphase I : The centrioles move to opposite poles and produce spindle fibres between the poles to separate chromosomes. Homologous pairs line up together across the equator of the spindle and are attached to the spindle fibres by the centromeres. Random assortment of chromosomes further increases variation.

Anaphase I : The centromeres split and homologous partners are pulled to opposite poles along the spindle fibres.

Telophase I :A new nuclear membrane forms around each collection of chromosomes at the opposite poles of the cell. The cytoplasm splits to form 2 haploid cells.

Both of these haploid cells undergoes Meiosis II. Meiosis II is exactly the same as Mitosis to double the number of cells.

Prophase II : Nuclear membrane disappears and the chromosomes shorten and thicken.

Metaphase II : Centrioles move to opposite poles and produce spindle fibres as before. Chromosomes align along the equator of the cell attached by their centromeres.

Anaphase II : The centromeres split and chromatids are separated to opposite poles.

Telophase II : A new nuclear membrane forms around each group of chromatids (now called chromosomes). The cytoplasm splits to form 4, genetically different, haploid gametes.

Sorry if this is too long winded, hope it helps!