Download recessive

Pedigrees
•
A Pedigree allows you to trace an inherited
(genetic) disease through a family.
• Pedigrees are NOT family histories.
• The pattern of a pedigree helps determine:
1. If the disease is inherited
2. If the disease is dominant or recessive
• Pedigrees use standardized symbols
Sickle Cell Disease Pedigree
Translating family information into
pedigrees
A girl with a genetic disease has 2 sisters
and one brother. Her brother has the
same disease, but her sisters do not. Her
mother has the disease but her father
does not.
Draw pedigree here:
Dominant or recessive?
Copy these pedigrees into your notes
1. For each case, determine whether the disease
is dominant or recessive
2. Assign genotypes for each individual
Case #1
Case #2
Case #3
“Guess and check”- Case #1
aa
aa
aa
aa
If the disease is DOMINANT:
A?
• All individuals without the disease must
be homozygous recessive.
• All individuals with the disease must
have at least one dominant allele (they
are either homozygous dominant, or
they are heterozygous)
Is this possible?
• NO, the person with the disease could not inherit a
dominant “A” if both parents have only “aa”
genotypes.
“Guess and check”- Case #1
A a?
A?
A a?
A?
aa
If the disease is RECESSIVE:
• All individuals with the disease must be
homozygous recessive.
• All individuals without the disease must
have at least one dominant allele (they
are either homozygous dominant, or
they are heterozygous)
Is this possible?
• YES, the person with the disease could inherit a
recessive “a” if both parents are heterozygous “Aa”
• Therefore, this pedigree shows a recessive disease.
Case #2- Dominant or recessive?
Try dominant disease alleles:
Try recessive disease alleles:
Is dominant possible?
Is recessive possible?
Case #3- Dominant or recessive?
Try dominant disease alleles:
Try recessive disease alleles:
Is dominant possible?
Is recessive possible?