Sources of variation
All humans belong to the same species, Homo sapiens. All humans share similar characteristics such as a nose, a similar body shape, two arms etc. Despite these similar characteristics, no two people are the same, including identical twins. Humans differ in ways like weight, skin colour, eye colour etc.
The differences between members of a species is referred to as variation. Variation in humans is the changes in the physical and mental state of a person that renders them unique.
The differences between members of a species is referred to as variation. Variation in humans is the changes in the physical and mental state of a person that renders them unique.
Genetic Variation
Genetic variation refers to the diversity in gene sequences. As mentioned in the previous chapter, mutations are the ultimate source of genetic variation along with sexual reproduction
Crossing overCrossing over is a big factor in promoting genetic diversity of organisms.
Crossing over is the exchange of genes between two chromosomes, resulting in different chromatids that make up the genetic material of gametes. This happens during meiosis and is able to occur because the chromatids of one chromosome, attached to the centromeres, become tangled with the chromatids of another chromosome. This causes the chromatids to break off their original chromosome and reattach to the chromosome that they were tangled with. The result is a new combination of genetic information that is different to the original chromosome. |
Non disjunction
Non-disjunction is the failure of the homologous chromosomes to separate during the period known as anaphase during a cellular division. During the first meiotic division, the homologous chromosomes pair and then separate. Occasionally, the pairs of chromosomes fail to separate when the cell divides. These situations are called non-dis junctions. The result of non-disjunction is one daughter cell receiving an extra chromosome and the other daughter cell, missing a chromosome. If this occurs in humans, the resulting gametes will posses either 24 chromosomes or 22 chromosomes instead of the usual 23. This will produce unexpected characteristics when during fertilization as the combined number of chromosomes will wither be two more or two less than the usual number.
Random fertilization
Another way of promoting genetic diversity is Random fertilization. Random fertilization is a random event that involves the gametes (sperm and egg cell). Whilst females can only release one egg at a time, males can produce hundreds of thousands of sperm all of which are slightly genetically different. Therefore, during fertilization, there is a huge variety of genetic variation as anyone of the genetically unique sperm can fertilize the egg. The resulting offspring is unique to that specific sperm that fertilized the egg. In other words, if another sperm had fertilized the egg, the genetic make up of the off-spring would have been different to that of the original offspring.