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How does the OCA2 Gene Affect Eye Colour in Humans?

By: Abeer Ahmed [999009530]

Alexx Riemenschneider [998872787]

Jessica Lyjak [998852987]

Gajan Santhiraswaran [998961903]

T.A: Alvin

PRA: 0305

BIO152H5F

1) Ewelina Pośpiech, et al. Gene-gene interactions contribute to eye colour variation in humans. Journal of Human Genetics 56, 447-455 (June 2011). Nature Publishing Group. 15 Nov 2011.

2) Gu Zhu et al., A Genome Scan for Eye Color in 502 Twin Families: Most Variation is due to a QTL on Chromosome 15q, Twin Research April 2004, Volume 7, Issue 2, 15 Nov 2011.

3) Matheny, A. P., and A. B. Dolan. "Changes in Eye Colour during Early Childhood: Sex and Genetic Differences." Annals of human biology

4) Mengel-From, J. Human eye colour and HERC2, OCA2 and MATP. Forensic science international: genetics 4.5 2010: 323-328. Elsevier. 15 Nov 2011.

5) Sturm, R. et al. Genetics of Human Iris Colour and Patterns. Pigment Cell and Melanoma Research. 544- 562. [2009].

References

Outline

Definitions

Background

Central Concept

-OCA2, effective and common gene

-found on chromosome 15q

-determines brown eye color and brown hair

Central Concept (OCA2)

-two types of OCA2 coding regions:

  • Arg305Trp allele
  • Arg419Gln allele

(responsible for brown, green, or hazel eye colours)

Impact of Melanin Production

Impact Melanin Production

(cc) photo by Franco Folini on Flickr

-melanin pigment in the iris causes complex patterns

-the OCA2 gene encode for what is known as the P-protein

-the P-protein is found in melanocytes, and encodes for the pigment, melanin

-brown iris, there's an abundance of melanin

-blue iris, lack of melanin

Light & the Eye

Mendelian Traits

(cc) photo by Metro Centric on Flickr

Mendelian Traits

(cc) photo by jimmyharris on Flickr

-can be explained by the Mendelian dominant-recessive gene model

Definitions

-two critical reports support Mendelian traits.

http://kentsimmons.uwinnipeg.ca/cm1504/mendel.htm

-some studies contradict Mendelian traits

  • melanin: a dark brown to black pigment found in the skin, hair, eyes, and iris of people and animals

Conclusion

  • melaninocytes: a mature melanin-forming cell, typically found in the skin

(cc) photo by Metro Centric on Flickr

Light & the Eye

  • Oculocutaneous albinism- A genetic disorder occurring in 10 types, ocular albinism occurs in the eyes

Questions

-iris color is dependant on how various shades of light reflect on it

-lengths and fibres of light effect the shade of light

  • OCA1(oculocutaneous albinism I): is a gene mutation, it metabolizes the amino acid tyrosine (which is essential for the conversion of melanin)

References

-iris dilates and contracts based on the amount

of light entering the eye

  • OCA2 (oculocutaneous albinism II): is a gene that provides information for making a protein that produces the melanin pigment.
  • biomarkers- a measurable substance in an organism which indicates a phenomenon such as disease, infection, and environmental exposure

Background

Questions??????

?????????????????

-the iris is the coloured part of the eye, around the pupil

http://upload.wikimedia.org/wikipedia/commons/6/65/Eye_iris.jpg

http://pjparlapiano.blogspot.com/2011/07/myriad-owns-your-genes.html

-melanin pigment in the iris is responsible for the resulting eye colour

-genes HERC2, OCA2, and MATP/SLC25A2 influence eye colour

-gene being focused on will be OCA2

-Heterochromia Iridis/Iridum: rare genetic disease that results in two different iris colours

-The iris is made up of 5 layers:

  • anterior border layer
  • stroma
  • sphincter
  • dilator muscle fibers
  • posterior pigment epithelium

-74% of eye color variance is due to an interval on

chromosome 15 that codes for variance

http://upload.wikimedia.org/wikipedia/commons/thumb/8/82/Cat_Eyes.jpg/800px-Cat_Eyes.jpg

Hetero = two

Chrom= colour

http://en.wikipedia.org/wiki/List_of_Greek_and_Latin_roots_in_English

-production of melanin will determine what eye colour an individual will have

-the more melanin produced, the darker the individual’s eye colour

-melanin helps protect the eye from UV rays (and other high frequency light)

-individuals with lighter coloured eyes (blue, green or grey) are at a higher risk of sun-related eye problems

Conclusion

http://4.bp.blogspot.com/_JjQLfjiMX7k/S9owKTSCVpI/AAAAAAAAAA4/eMM8OpEbqSs/S640/sunglasses_gaga_justdance.jpg

FUN FACTS!!!!!

  • The iris is vital in acting as biomarkers for purposes such as personal identification based on iris patterns, instead of using fingerprinting

  • Markers have also been associated with eye diseases such as glaucoma, Down syndrome, and other neurological disorders, proving that there is an association between the iris and brain development

- eye colour

is mostly

dependent

on genetics

-OCA2 is a great contributer

to melanin production,

making it the most

valuable in producing

eye colour

-it is undetermined whether eye colour is

predictable, but as far as we know

it is very much influenced by genetics

-the amount of melanin determines

what kind of colour the iris will be:

  • a lot will make darker colours such as brown
  • a little will make lighter colours like blue
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