Differences in appearance between offspring from the same parents may be due to environmental factors which can then be divided into subunits including Ageing e. g. Loss of elastin and moisture in your skin as you age causes wrinkles, your back may start to arch or loss of teeth etc. lifestyle choices for example it may be that you dye your hair or use makeup or the way you style you hair etc. or diseases such as Elephantitus causes limbs to swell, Jaundice gives skin a yellowish pigment etc.
These factors are just some of the ways in distinguishing you from your siblings from the same parents. Genetic Factors Alternatively your genetic make-up also plays a part in your appearance as it affects your height, natural eye and hair colour, Skin colour, gender etc. and this is due to the variety of genes that you end up with from your parents during meiosis. First you need to know that genes are sections of DNA (DNA holds the genetic information) and are found on the surface of chromosomes and they contain instructions to make proteins.
The base sequence of the gene determines the Amino acid sequence and so in turn will determine the proteins/enzymes made that will eventually determine what we look like (our Phenotype). Mutations in the DNA base sequence can produce new alleles of genes. Alleles are different forms of the same gene e. g. they both code for hair colour but one codes for brown hair and the other codes for blonde hair. Which is part of the reason there is variation in appearance.
Meiosis is the process that is used during sexual reproduction and it explains how cells divide to form two daughter cells with half the number of chromosomes (haploid cells) and these are all genetically different due to having a combination of maternal and paternal chromosomes. As well as this to further increase genetic diversity, during one of the stages of meiosis known as prophase, genetic information is crossed over between chromatids so each cell has a different set of alleles.
Genetic diversity between the children is also caused because all of the daughter cells during meiosis have a different combination of maternal and paternal chromosomes (half from your mum and half from your dad). When the gametes are produced different combinations of these chromosomes go into each cell. This is known as Independent segregation of chromosomes. This explains why we look genetically different in appearance from our siblings from the same parents.