Question

 Describe at least 3 different ways that meiosis and sexual reproduction increases genetic variability in offspring. What advantage does that give sexually reproducing organisms over asexually reproducing organisms? When is asexual reproduction an advantage over sexual reproduction?

Answer 1

The three main sources of genetic variation arising from sexual reproduction are: Crossing over (in prophase I) Random assortment of chromosomes (in metaphase I) Random fusion of gametes from different parents

Crossing Over. The main cause of variation during sexual reproduction comes during development of gametes during meiosis. During Pachytene( Prophase I of meiosis I) interchange of chromosomal segments happens between non sister chromatids. This interchange of chromosomal segment is basis for most of the variability during sexual reproduction. It is also key driver of new recombinant formation and evolution

Independent assortment of chromosome :

each cell that carries out meiosis has 23 pairs of homologous chromosomes. Each chromosome in a pair can have slightly different versions of the same gene. Independent assortment is the process in which each homologous chromosome in a pair goes into a separate gamete. Thus, each gamete has only one copy of each gene and that copy may be a different version of the same gene that is in another gamete.

Random Fertilisation

The fusion of two haploid gametes results in the formation of a diploid zygote

• This zygote can then divide by mitosis and differentiate to form a developing embryo

As meiosis results in genetically distinct gametes, random fertilisation by egg and sperm will always generate different zygotes.

Advantage of asexual reproduction over sexual reproduction- In asexual reproduction, there is no sexual defferentiation in both the parents like male and female. So, both parents are individually capable of increasing progeny. The male or female parent does not need to wait for chance meeting of other type of gamets. Hence, number of progeny becomes almost double in case of asexual reproduction.