ALBINISM

Greer Manton, Sydney Gilbert & Monica Starbinski

2/1/10 – Period 2

Please be respectful during this PowerPoint. The photos you may see today are unlike many others. Keep in mind that they are of real people, and you never know if someone has a person close them that has this.

Thank You,Sydney, Monica and Greer

What Chromosome?

•Albinism is a genetic order, which is caused by a gene on the ninth X (female) chromosome.

Alleles

• Alleles – an alternative form of a gene, which is located on a specific part of a certain chromosome.

• 2 alleles per human gene.

Recessive (aa):-trait will only

appear if a dominant allele is not present.-homozygous

Dominant (AA, Aa):

-overpowers the recessive

allele.-heterozygous

Summary Of Albinism• Albinism – a rare, inherited, disease that you are born with, causing a lack in pigment or melanin. Usually, the person’s hair, eyes, and skin are affected.• Symptoms –

Extremely light colored skin light/white colored hair pale blue/grey eye color, sometimes even pink very high risk of sunburn and skin cancer vision problems*Interesting Facts*There is no cure for Albinism, but precautions can be taken to alleviate the symptoms.

- Staying out of the sun- contacts or seeing an optician

Mode Of Inheritance

•Albinism is recessive.• A male would have to inherit one affected X chromosome and females would have to inherit two affected X chromosomes to have the disorder.• It is not dominant because you do not get it every time, if one parent is a carrier. Both parents must contain the gene, whether they have the disease or not.• It is autosomal because you need two copies of the affected gene in order for albinism to occur.

Punnett SquaresA – dominant (normal gene)

a – recessive (affected albinism gene)

A

a

a a

a A

a

A

a A

A

A

Aa Aa

aa aa

Aa Aa

Aa Aa

aa Aa

Aa Aa

Probabilty

• Ratios1 : 2 : 11aa : 2Aa : 1AA

A

a

A

a

• Percentages25% : 50% : 25%25% aa : 50% Aa : 25%AA

Aa AA

aa Aa

Genotype and Phenotype Probability

A

A

a

a

• Phenotype -Ratios – 3 no albinism : 1 albinism

-Percentages - 75% no albinism : 25% albinism• Genotype

- Ratios – 1AA : 2Aa : 1aa- Percentages – 25%AA :

2Aa :aa

Aa AA

aa Aa

Hypothetical Pedigree

KeyWhite – Healthy unaffected person. May carry one albinism gene.Orange – Affected with albinism, has two of the damaged genesStar – femaleRectangle - Male

Laura Jonathon

Andrew Leah Nick Claire

GeorgeMary Max KimAshley

Emma

Meaning of the Albinism Punnett Square

• AA – means that both genes are normal and they dominate. Aa – means that one gene is normal and one is affected with albinism. But since there is a normal gene that is dominant, it overpowers and the person is unaffected. aa – means that both genes are affected and the person has albinism• Phenotype (what is SEEN)

if AA then normal brown hair is presentif Aa then normal brown hair is present but

the person is a carrier of the white hair geneif aa then the person has white hair.

• Genotype (what is in the GENES)AA – Homozygous DominantAa – Heterozygous Dominantaa – Homozygous Recessive

Student Practice

Aa

a

a

Genotype:

Ratio –Percentages –

Phenotype:Ratio – Percentages –

aa

aa

Aa

Aa

2 albinism : 2 no albinism

50% albinism : 50% no albinism

50% aa : 50% Aa

2 aa : 2 Aa

Hypothetical Pedigree (Student Practice)•Choose a Female and

a Male•Who is married to who•The children they have•And probability of them being affected.

The Rest is up to you!

Key:

•Pick 2 colors.•One for non effected•One for affected

Pedigree Question and Answer:

1.How many affected parents are needed to produce a child with albinism? –

2.What are the chances that the next generation of children will get albinism if only one parent has the bad gene? -

3.If both parents carry the gene what’s the chance that the child will not get albinism? -

Two parents both with the affected gene.

no chance.

50% chance