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There are differences that people are not born with and are due to the environmental factors. These factors can be caused by having scars, tattoos, unnatual dyed coloured hair and piercings. This is casued by not just the by the physical surroundings  but by the social situation thye live in.

However some can be due to a combination as where a parent may be obese and this can be casued by genetics but also the evironment and lifestyle they live in. The environmental factor is that you can eat too much food and do very little excercise. 

Human eye colours are not determined by one gene only as it doesn't follow a simple pattern of inheritance. As a result there is a wide range of eye colours in humans which is an example of continous variation. This is a wide range of possibile outcomes.

The genetic makeup of an induvidual organism is called the genotype.  The gentype is the combination of alleles that the organism has.

The characterstics that an induvidual displays are called the phenotype. The phenotype is that its obvservable physical characterists. 

The genotype can be a main influence on the phenotype although sometimes it can also be casued by the environment, whichc can determinate the physical characteristcs of an organism.

Identical twins are produced when one zygote splits into two and each of these cells produce into a baby, Idenical twins have identical genotypes. Non identical or fraternal twins are grown from two sperate egg each fertilised by a different sperm, so they are able to have diffent genotypes just like other siblings. 

Chromosomes are twisted and folded structures which can be used for storage. Human cells have 23 pairs and so 46 chromosomes in total in most human cells. Chrormosomes are found in the centre of a nuclues, where the sperm andf egg cells have 23 chromsomes. When the sperm and egg join together fertilisation has been formed and a new cell is called a zygote that also has 46 chromosomes, 23 each form each parent. 

Pairs of chromosomes usually contain the genes for the same trait in the same position. The alternative forms of the genes are called alleles. Offsprings get one of each pair of chromosomes from mother and father.

(http://www.eschooltoday.com/science/genetics/images/inheritance-chart.jpg)

Alleles can be dominant or reccssive. When the alleles in a pair are dfferent from each other, the trait shown in the offspring would  be dominant alleles. 

Dominant alleles controls the development of a characteristic even if it is present on only one chromosome in a pair. This is written with capital letters

Recessive alleles contols the debvelopment of a characteristic only if a dominant allele is not present and it can be when both recessive in a pair of chromosomes.

Mutations can sometimes occur as a  mistake of creating cells or duing fertilisation. This can lead to some people have a more or less chromosomes than the original 46. 

During a pregnancy and when the woman knows that she has a baby with…

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