Question

Mention two main causes of variation during reproduction.

Answer 1

Hint: Variations are the changes in the genome that make the offspring different from the parent. It is necessary for evolution as it results in the survival of a species and leads to the formation of new species.

Complete answer:
The production of offspring through the formation and fusion of gametes is known as sexual reproduction.
Sexual reproduction results in offspring that have genetic material which is different for their siblings or their parents.

Meiosis Promotes Genetic Variation-
There is a formation of different sets of chromosomes after meiosis. Because genes are located on chromosomes, and often come in different forms (alleles), each cell produced by meiosis receives a different complement of alleles for its genes. The offspring produced are genetically different from each other and from their parents.
When meiosis and outcrossing occur, the chromosome complements of offspring differ from one another and from their parents for three reasons:
-Gametes receive a random assortment of maternal and paternal chromosomes when homologs separate in meiosis I. This is an independent assortment.
-Because of crossing over, each chromosome contains a random assortment of paternal and maternal alleles.
-Outcrossing results in a combination of chromosome sets from different individuals.

Fertilization is another reason for genetic variation-
As long as some alleles vary in a diploid individual, crossing over and the independent assortment of maternal and paternal chromosomes ensure that each gamete is genetically unique. These differences between gametes lead to another important source of genetic variation—the random union of gametes at fertilization. Even if two gametes produced by the same individual fuse to form a diploid offspring—in which case self-fertilization, or “selfing,” is taking place—the offspring still will be genetically different from the parent. Selfing is common in many plant species, and it also occurs in animal species in which single individuals— hermaphrodites— contain both male and female sex organs.

Note: - When both sister chromatids in meiosis II or homologous in meiosis one goes in one daughter cell, the meiosis will cause abnormalities.
This error is known as nondisjunction because the homologs or sister chromatids fail to separate or disjoin.
 -If the n - 1 gamete is fertilized by a normal n gamete, the resulting zygote will be 2n - 1. This situation is called monosomy because there is only one copy of one of the chromosomes. Cells that have too many or too few chromosomes of a certain type are known as aneuploid.