Download Polydactyly+Final

1-28-10
Period 2
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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
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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 gene
 You get one of the two alleles in a gene from your father and
the other from your mother
 Recessive alleles are represented by the letter of the
characteristic in lower-case form
 Dominant alleles are represented by the letter of the
characteristic in capital
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
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
G
g
G
GG
Gg
g
Gg
gg
Heterozygous
Homozygous
w
w
W
Ww
Ww
W
Ww
Ww
h
h
h
hh
hh
h
hh
hh
G
G
g
g
• Ratio
1GG
GG
Gg
2Gg
1gg
Gg
gg
• Percentage
25% -GG
50% - Gg
• 75% chance of getting Polydactyly
• 25% chance of not getting Polydactyly
25% - gg
G
g
G
GG
Gg
g
Gg
gg
•Top – Father
•Left – Mother
GG – two dominant alleles
Gg – one dominant allele and one
recessive allele
gg – two recessive alleles
• Phenotype
GG = Recieve polydactyly
Gg = Receive polydactyly
gg = Normal amount of fingers
• Genotype
GG = Homozygous dominant
Gg = Heterozygous dominant
gg = Homozygous recessive
G
G
g
g
GG
Gg
Gg
gg
• 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
•Genotype
Ratio – 1 GG; 2 Gg;
G
g
GG
Gg
Gg
gg
1gg
Percentage –
75% chance receive disease
25% chance of not getting
disease
• Phenotype
Ratio – 3 with
Polydactyly; 1 without
Polydactyly
Percentage – 75% of
getting Polydactyly
Female – circle
Male – 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; one dominant
gene one recessive allele
All black homozygous
dominant. Has the
disease.
Student Practice
Key –
• circle – female
• square – male
• shaded in (blue) –
two dominant
alleles
• not shaded – two
recessive alleles
• half shaded – one
dominant and one
recessive allele
Questions????????
• If two parents are homozygous dominant, how likely
would it be for a child not have the disease?
•0% child would wind up homozygous dominant
• If one parent is homozygous dominant but another is
homozygous recessive, is it possible for one of the
children not to obtain the disease?
•Each of the children will wind up
heterozygous dominant
• If one parent were heterozygous dominant and
homozygous recessive, how likely is it for a child to get
the disease?
50%