Sources of Variation
Variation is the differences between members of a species. In humans, this can refer to eye colour, height, weight, skin colour, body proportions etc. Variation is partially a result of environmental factors for example your parents will give you your base colour for your skin e.g. white skin, this can be altered in time with consistent exposure to the sun.
For a further detailed explanation: http://www.britannica.com/EBchecked/topic/623389/variation
For a further detailed explanation: http://www.britannica.com/EBchecked/topic/623389/variation
Random assortment of chromosomes during meiosis
When two gametes unite at fertilisation, the resulting cell is a combination of genes from each parent. So when 23 chromosomes from one parent meet with the 23 from the other, the chromosomes match up and control each other thus existing in homologous pairs. During the first meiotic division, the pair of chromosomes split, moving to either pole and do so at random.
Refer to this website for more detail: http://highered.mheducation.com/sites/9834092339/student_view0/chapter11/random_orientation_of_chromosomes_during_meiosis.html
Watch this video for a visual representation: http://www.youtube.com/watch?v=-Zzp3mLIycM
When two gametes unite at fertilisation, the resulting cell is a combination of genes from each parent. So when 23 chromosomes from one parent meet with the 23 from the other, the chromosomes match up and control each other thus existing in homologous pairs. During the first meiotic division, the pair of chromosomes split, moving to either pole and do so at random.
Refer to this website for more detail: http://highered.mheducation.com/sites/9834092339/student_view0/chapter11/random_orientation_of_chromosomes_during_meiosis.html
Watch this video for a visual representation: http://www.youtube.com/watch?v=-Zzp3mLIycM
Crossing Over
When the homologous chromosome pair during the first meiotic division the chromatids get tangled with each other and this is known as crossing over. The point where two chromosomes cross is known as a chiasma. The chromatid may also break in this occurrence and would then join up with a chromatid of a different chromosome. This results in a different line up of chromosomes known as recombination.
Look at these websites for more information:
video: http://www.youtube.com/watch?v=rqPMp0U0HOA
website: http://www.accessexcellence.org/RC/AB/BC/Genetic_Recombination.php
When the homologous chromosome pair during the first meiotic division the chromatids get tangled with each other and this is known as crossing over. The point where two chromosomes cross is known as a chiasma. The chromatid may also break in this occurrence and would then join up with a chromatid of a different chromosome. This results in a different line up of chromosomes known as recombination.
Look at these websites for more information:
video: http://www.youtube.com/watch?v=rqPMp0U0HOA
website: http://www.accessexcellence.org/RC/AB/BC/Genetic_Recombination.php
Non-disjunction
Non-disjunction occurs when one or more chromosome pairs fail to separate when the cell divides during the first meiotic division. In the second meiotic division, one or more chromatids may also then fail to separate. This results in one or more daughter cells receiving an extra chromosome than the other. The resulting zygote will therefore have 47 or 45 chromosomes. This would produce unexpected characteristics in the offspring and usually, in humans, birth defects and miscarriage can often occur as a result.
Trisomy: is where an individual inherits an extra copy of a chromosome instead of normally two. One being trisomy 21, or Down's syndrome.
Monosomy: is where an individual is missing a chromosome. This usually results in severe malformations and often miscarriage
Partial monosomy and trisomy: Partial Monosomy is where part of a chromosome is missing and partial trisomy is where an extra chromosome is attached to one of the other chromosomes.
Website: http://en.wikipedia.org/wiki/Nondisjunction
Non-disjunction occurs when one or more chromosome pairs fail to separate when the cell divides during the first meiotic division. In the second meiotic division, one or more chromatids may also then fail to separate. This results in one or more daughter cells receiving an extra chromosome than the other. The resulting zygote will therefore have 47 or 45 chromosomes. This would produce unexpected characteristics in the offspring and usually, in humans, birth defects and miscarriage can often occur as a result.
Trisomy: is where an individual inherits an extra copy of a chromosome instead of normally two. One being trisomy 21, or Down's syndrome.
Monosomy: is where an individual is missing a chromosome. This usually results in severe malformations and often miscarriage
Partial monosomy and trisomy: Partial Monosomy is where part of a chromosome is missing and partial trisomy is where an extra chromosome is attached to one of the other chromosomes.
Website: http://en.wikipedia.org/wiki/Nondisjunction
Random fertilisation
Random fertilisation is the term used when stating that during fertilisation, any male sperm can fuse with any female egg creating a zygote. There is no way of determining which exact sperm or egg is going to be used and therefore a source of variation occurs as a result of sexual reproduction. A female may only release one egg at a time, but a male can release hundreds of millions of sperm, all being slightly different to one another. The uniting of sperm and egg therefore is relied completely on chance. The resulting offspring also ultimately has a different set of alleles to either of its parents.
Video: http://www.youtube.com/watch?v=h33ZnlLM49g
Random fertilisation is the term used when stating that during fertilisation, any male sperm can fuse with any female egg creating a zygote. There is no way of determining which exact sperm or egg is going to be used and therefore a source of variation occurs as a result of sexual reproduction. A female may only release one egg at a time, but a male can release hundreds of millions of sperm, all being slightly different to one another. The uniting of sperm and egg therefore is relied completely on chance. The resulting offspring also ultimately has a different set of alleles to either of its parents.
Video: http://www.youtube.com/watch?v=h33ZnlLM49g
Accepting human variations
Human have a variety of different characteristics but are still classed under the same species- Homo sapiens. As a species, humans are organisms that have many characteristics and can breed under natural conditions but cannot interbreed with another species. because there is such variation in human species, scientists have attempted to classify humans into groups or races based on their physical attributes and from where they originated from. But as there are so many different variations, the attempting to group people became unworkable. The diversity that occurs between each human is just so great that biologists simply cannot group people because it serves no useful purpose.
website: http://en.wikipedia.org/wiki/Human_variability
Human have a variety of different characteristics but are still classed under the same species- Homo sapiens. As a species, humans are organisms that have many characteristics and can breed under natural conditions but cannot interbreed with another species. because there is such variation in human species, scientists have attempted to classify humans into groups or races based on their physical attributes and from where they originated from. But as there are so many different variations, the attempting to group people became unworkable. The diversity that occurs between each human is just so great that biologists simply cannot group people because it serves no useful purpose.
website: http://en.wikipedia.org/wiki/Human_variability
Britannica. (n.d.). Variation. Retrieved October 9, 2014, from Britannica: http://www.britannica.com/EBchecked/topic/623389/variation
click4biology. (n.d.). 3.26 Random fertilisation . Retrieved October 9, 2014, from YouTube: http://www.youtube.com/watch?v=h33ZnlLM49g
Crossing-over: Genetic Recombination. (n.d.). Retrieved October 9, 2014, from Access Excellence: http://www.accessexcellence.org/RC/AB/BC/Genetic_Recombination.php
S-Cool. (n.d.). Variation. Retrieved October 9, 2014, from S-Cool: http://www.s-cool.co.uk/gcse/biology/genes-and-genetics/revise-it/variation
unknown. (n.d.). Genetics Physician Salary. Retrieved October 6, 2014, from MD Salaries: http://mdsalaries.com/2011/11/10/genetics-physician-salary/
Wikipedia. (n.d.). Human Variability. Retrieved October 9, 2014, from Wikipedia: http://en.wikipedia.org/wiki/Human_variability
Wikipedia. (n.d.). Huntington's Disease. Retrieved october 6, 2014, from Wikipedia: http://en.wikipedia.org/wiki/Huntington's_disease
Wikipedia. (n.d.). Nondisjunction. Retrieved October 9, 2014, from Wikipedia: http://en.wikipedia.org/wiki/Nondisjunction
DocBerends. (n.d.). Meoisis: Independent Assortment of Homologous Chromosomes . Retrieved October 9, 2014, from YouTube: http://www.youtube.com/watch?v=-Zzp3mLIycM
HD, B. /. (n.d.). Meiosis: Crossing Over and Variability [3D Animation] . Retrieved October 9, 2014, from YouTube: http://www.youtube.com/watch?v=rqPMp0U0HOA
click4biology. (n.d.). 3.26 Random fertilisation . Retrieved October 9, 2014, from YouTube: http://www.youtube.com/watch?v=h33ZnlLM49g
Crossing-over: Genetic Recombination. (n.d.). Retrieved October 9, 2014, from Access Excellence: http://www.accessexcellence.org/RC/AB/BC/Genetic_Recombination.php
S-Cool. (n.d.). Variation. Retrieved October 9, 2014, from S-Cool: http://www.s-cool.co.uk/gcse/biology/genes-and-genetics/revise-it/variation
unknown. (n.d.). Genetics Physician Salary. Retrieved October 6, 2014, from MD Salaries: http://mdsalaries.com/2011/11/10/genetics-physician-salary/
Wikipedia. (n.d.). Human Variability. Retrieved October 9, 2014, from Wikipedia: http://en.wikipedia.org/wiki/Human_variability
Wikipedia. (n.d.). Huntington's Disease. Retrieved october 6, 2014, from Wikipedia: http://en.wikipedia.org/wiki/Huntington's_disease
Wikipedia. (n.d.). Nondisjunction. Retrieved October 9, 2014, from Wikipedia: http://en.wikipedia.org/wiki/Nondisjunction
DocBerends. (n.d.). Meoisis: Independent Assortment of Homologous Chromosomes . Retrieved October 9, 2014, from YouTube: http://www.youtube.com/watch?v=-Zzp3mLIycM
HD, B. /. (n.d.). Meiosis: Crossing Over and Variability [3D Animation] . Retrieved October 9, 2014, from YouTube: http://www.youtube.com/watch?v=rqPMp0U0HOA