Question

Describe three (3) specific ways human sexual reproduction produces genetic diversity in offspring.

Consider this hypothetical situation: you are heterozygous for an autosomal recessive genetic disorder and your potential reproductive partner is also heterozygous for that same recessive genetic disorder.

a. Do you and your potential partner exhibit the recessive phenotype?

b. What is the probability the offspring of this breeding pair will have the recessive phenotype?

c. Would you have children with this person? Why or why not?

d. Should people known to be carriers of a recessive genetic disorder be legally prohibited from having children? Why or why not?

Answer 1

Genetic variability forms the basis of reproductive supremacy of sexual reproduction over asexual mode of reproduction.It is important because over the course of time it plays a characteristic role in evolution and in providing that adaptability towards changing environment. In a population ,there can be a different alleles for a single gene loci. While some of the alleles can be beneficial in better survival others can prove to be fatal. This provides a basis for natural selection for the superior alleles .This variation in the alleles of genes present in a population can be introduced in two ways:

1. Mutation

2. Sexual Reproduction

Here we will discuss how sexual reproduction introduces genetic variability. This is done in three :

• Crossing over of homologous chromosomes during Prophase1 of Meiosis 1 in the parents during gametogenesis.

In a human being there are 46 chromosomes in the form of 23 pairs. Each pair consists of two chromosomes having the same genes in the same gene loci, one from the maternal origin and other from paternal origin. During prophase one they line up beside each other and exchange bits of them which produces genetic variability as shown below.This happens to every chromosome pair.Chromatids that contain pits of both parents are known as recombinants and thus are unique.

• Random distribution of chromosomes into the gamete. During metaphase 1 of meiosis 1 the homologous chromosomes lineup in the equator facing opposite poles in a random orientation. After this half a set of chromosomes travelled to opposite poles and form a cell with haploid set. In the next step i.e meiosis 2 equational division occur. In metaphase 2 of meiosis 2 the sister chromatids separate and travel into opposite poles forming two more haploid cells. As we know that from the previous metaphase the chromosomes already have sister chromatids out of which one is of either maternal or paternal origin and the other is recombinant, these chromatids gets independently assorted into the gametes thus the alleles of genes also get independently assorted along with it. Theere can be number of combinations based on the formula 2n where n is number of haploid chromosomes. One such probability where n is 3 is shown below.In humans n is 23 hence number of unique combinations possible is quite huge . This random orientation or independent assortment is the major source of genetic variation in sexual reproduction.
• Random fertilisation : fertilisation restores the diploid chromosomal number.When the gametes fuse, the zygote developed carries chromosomes from both parents in a unique combination, with some similarities to the parents. This event is completely random and results in variation.

a: For a autosomal recessive disorder, the heterozygous individuals are usually clinically normal carriers of the trait. They donot show the phenotype. There for me and my partners will not exhibit the recessive phenotype.

b: c: theoretically analysing from the above Punnet  square analysis I would not prefer having kids with his partner because there is half the probability of having carrier offsprings that will further increase the fatal mutated allele frequency in the population. Also a quarter of the kids might be sufferers. So it will be wiser to not have kids.

d: Legally speaking every individual has the liberty to choose his or her own partners and the right to bear kids. We cannot prohibit people from having kids hence one way in which a fatal allele can be eliminated from the population is by advising carriers and sufferers not to have kids with other carriers or sufferers. Rather opt to have kids with normal n fit people with no mutated allele.