Download Human Genetic Disorders

Human Genetic
Disorders
A genetic disorder is an abnormal
condition that a person inherits
through genes or chromosomes.
Genetic disorders are caused by
mutations, or changes in a
person’s DNA.
Human Genes and Mutations
• Mutations happen when an error occurs
while copying the DNA sequence
• Not all mutations are harmful, some are
beneficial and others have no effect at all
• Certain chemicals, x-rays and radioactive
substances can cause mutations
Chromosome Disorders
• Individual, or point, mutations can occur, but an
error can occur with the number of
chromosomes that should be inherited
• These mistakes usually occur in meiosis
– Chromosome number is too many or too few
– Results from Non-disjucntion
• An incorrect number of chomosomes is often
fatal to an unborn embryo or fetus, or the baby
dies shortly after birth
– Down Syndrome-3 copies of Chromosome #21
Common Genetic Disorders
• Cystic Fibrosis
– Body produces abnormally thick mucus in the lungs and
intestines that can lead to bacterial infections
– Causes difficulty breathing and digesting
– It is a recessive allele (both parents must carry it) and has no
known cure
• Sickle-cell disease (Sickle-cell Anemia)
– Caused by abnormal hemoglobin (protein that carries oxygen)
causing pain and weakness
– The allele for it is co-dominant.
– People with two sickle cell alleles have it
– People with one sickle-cell allele produce
both normal and abnormal hemoglobin but
don’t usually have symptoms. There are
treatments but no cure.
Common Genetic Disorders cont.
• Hemophilia
– Disorder that causes the blood to clot slowly or not at all. One of
the proteins needed for normal clotting is not produced.
– It is caused by a recessive allele on the X chromosome and thus
is sex-linked.
– Occurs more often in males than females.
– Can develop after birth but usually genetic.
– http://www.sciencecases.org/hemo/hemo.asp
• Down Syndrome
– Due to an extra copy of chromosome 21
– Occurs when chromosomes fail to
separate during meiosis
– Down Syndrome patients have a distinct
appearance and some degree of mental
retardation but many lead full active lives
Modern Approach to Genetic
Disorders
• Doctors can detect genetic disorders using
amniocentesis and karyotypes
• Amniocentesis: chromosomes from fluid
surrounding the baby are examined
• Karyotype: a picture of the chromosomes
revealing whether the baby has the right number
or whether it is a boy or girl
• Couples with family histories of disorders must
weigh the chances of children having a disorder.
Karyotypes, pedigrees and Punnett squares can
help with determining the potential risks