1-28-10Period 2

Polydactyly is a condition in which a person has more than five fingers per hand or five toes per foot.

Polydactyly occurs in the womb; instead of developing only one thumb and four fingers an extra finger is added

Usually the hand is formed in the womb and when it is being split it is made into 4 fingers, 1 thumb. However sometimes an extra split occurs and abnormal number of fingers is produced

It is a autosomal dominate characteristic

The cause of the disorder is usually found on chromosome 13.

However for some cases it is not known

There is another gene or chromosome that the mutation could happen in that could cause polydactyly

Mode of Inheritance

Polydactyly is autosomal dominant. Autosomal dominant means that an

offspring can get this disease by having it passed down from just one parent.

Polydactyly occurs because of genetic disorders or errors in fetal development.

Polydactyly can also be a symptom for another disease.

Ex. – Bardet-Biedl syndrome Ex. – Bloom’s syndrome Ex. – Jeune’s thoracic dystrophy syndrome

What are Alleles? A person has two alleles per geneYou get one of the two alleles in a gene from your

father and the other from your motherRecessive alleles are represented by the letter of

the characteristic in lower-case formDominant alleles are represented by the letter of

the characteristic in capital R – Dominant r – Recessive

The dominant alleles and the recessive alleles both represent two different possible characteristics.

The “characteristic” will be dominant if the gene has one dominant allele or two dominant alleles

The “characteristic” will be recessive if the gene has two recessive genes only

GG Gr

Gr gg

Gg

G

g

Ww Ww

Ww Ww

w w

W

W

Heterozygous

Homozygous

hh hh

hh hh

hh

h

h

GG Gg

Gg gg

G g

G

g

• Ratio1GG 2Gg 1gg

• Percentage 25% -GG 50% - Gg 25% - gg

• 75% chance of getting Polydactyly

• 25% chance of not getting Polydactyly

GG Gg

Gg gg

G g

G

g

GG – two dominant allelesGg – one dominant allele and one recessive allelegg – two recessive alleles

• PhenotypeGG = Recieve polydactylyGg = Receive polydactylygg = Normal amount of fingers

• GenotypeGG = Homozygous dominantGg = Heterozygous dominantgg = Homozygous recessive

•Top – Father•Left – Mother

GG Gg

Gg gg

G g

G

g

• Phenotype- Ratios- 3 for polydactyly : 1 for

normal- Percentage – 75% chance of

polydactyly 25% chance of

normal # of f fingers

• Genotype - Ratios- 1 GG : 2 Gg : 1 gg - Percentages- 25% GG : 50%

Gg : 25%gg

G g

G

g

•GenotypeRatio – 1 GG;

2 Gg; 1ggPercentage – 75% chance

receive disease25% chance of not getting disease

• Phenotype

Ratio – 3 with Polydactyly; 1 without Polydactyly

Percentage – 75% of getting Polydactyly

GG Gg

Gg gg

Female – circleMale – Square

All green – homozygous recessive gene, person doesn’t have the disease, person has 2 healthy alleles

Half green, half black (or star) – heterozygous gene, person has the disease because you only one dominant gene with the disease to get it

All black homozygous dominant. Has the disease.

Student PracticeKey –• circle – female• square – male• shaded in (black) – two dominant alleles• not shaded (red) – two recessive alleles• half shaded – one dominant and one recessive allele

• If two parents are homozygous dominant, how likely If two parents are homozygous dominant, how likely would it be for a child not have the disease?would it be for a child not have the disease?

• If one parent is homozygous dominant but another is If one parent is homozygous dominant but another is homozygous recessive, is it possible for one of the homozygous recessive, is it possible for one of the children not to obtain the disease?children not to obtain the disease?

• If one parent were heterozygous dominant and If one parent were heterozygous dominant and homozygous recessive, how likely is it for a child to homozygous recessive, how likely is it for a child to get the disease?get the disease?

Questions????????

•0% child would wind up homozygous dominant0% child would wind up homozygous dominant

•Each of the children will wind up Each of the children will wind up heterozygous dominantheterozygous dominant

50%