Download Genetic Diseases

Title: Genetic Diseases
1- Autosomal recessive genetic diseases (disorders)
a- Autosomal means the defective gene is carried on one of the first 22
chromosomes (the autosomal chromosomes) and not on the sex
chromosomes (#23)
b- If you have one copy of the gene you are a carrier for the disease, but do
not have the disease
c- If you have two copies of the defective gene you have the disease
d-
e- Some common autosomal recessive disorders are
1- Cystic fibrosis – the most commonly inherited genetic disorder among
Caucasian people
2- Sickle cell anemia – the most common genetic disorder among black
people
3- Albinism is an autosomal recessive disorder that in seen in all races of
people and all species of animal
4- Phenylketonuria is an autosomal recessive disorder hat every
newborn in the United States is tested for
5- The “Jewish Genetic Disorders” These diseases are most common
among people of Ashkenazi origin. These diseases include: Tay-Sachs.
Niemann-Pick, Canavan’s Disorder, Bloom’s Disease, Familial
Dysautonomia and Fanconi Anemia
f- Problems
a- A Man with sickle cell anemia has woman with a children who is
homozygous normal. What are the chances they will produce a child
who is a carrier for this condition?
b- If one of the children in the above question has children with a
partner who is heterozygous for this condition what will the
genotypes and phenotypes of these children be?
2- Autosomal Dominant Genetic Disorders
a- There are no carriers for these diseases. If you have one copy of this gene
then you HAVE the disease.
b- These diseases are often fatal and people do not live long enough to pass
the gene on by having children. However, this is not always true
c- Huntington’s Chorea (disease) and polydactyl (extra fingers and toes),
Marfan’s syndrome and are examples of this type of inheritance.
d- Problems
1- A man who is heterozygous for Huntington’s has children with a
woman with the homozygous recessive genotype. What percentage of
their children will have Huntington’s disorder. What percentage of
their children will be healthy?
2- Two people both heterozygous for polydactyl have children. What
percentage of their children will have the normal number of fingers
and toes? One of their children who is homozygous dominant for the
trait has children with a woman who has the recessive phenotype.
How many of their children will have the dominant genotype. How
many will have the dominant phenotype?
3- Sex-Linked (or X-linked) genetic disorders
a- X-linked genetic disorders are carried on the X chromosome
b- The X chromosome is one of the two sex chromosomes
c- Sex – linked genetic disorders are passed from mother to son.
d- Women are carriers of the disease – They DO NOT have it, but with each
pregnancy they have a 50-50 chance of passing it on to their sons
e- Boys are not carriers – If they have the gene they have the disease
f- Examples of x-linked disorders are hemophilia (The Royal Disease of
Europe), color blindness, Duchenne’s Muscular Dystrophy and
Adrenoleukodystrophy (ALD)
g- It is possible for a woman to get one of these diseases, but only if the
woman is a carrier for the disease and the man has the disease. Most of
these diseases are fatal for young boys so they do not live long enough to
have children. Therefore it is rare for woman to have these diseases.
h- EXAMPLE
i- Problems
a- A woman who is a carrier for the colorblind gene has children with a
man who is colorblind. What percentage of their sons will be color
blind? Will any of their daughters be colorblind?
b- A woman who inherited the gene for hemophilia from her mother has
children with a man who does not have hemophilia. Using a Punnet
square show all the possible genotypes of their children. How would
we describe their phenotypes?
c- Use the information in question b. Assume modern medicine enables
one of her sons with hemophilia to have children with a healthy, noncarrier female. Will any of their children have hemophilia? Will any of
the children be carriers?