CHROMOSOMES AND HUMAN INERITANCE
I. HUMAN CHROMOSOMES
A. Human cells contain 23 pairs of chromosomes. That is a total of 46 chromosomes per cell.
B. Human Chromosomes are classified as follows:
1. 22 pairs of Autosomesa. Structurally, autosomes are similar; however, they do contain different genes.
b. These are responsible for providing us with traits such as
2. 1 pair of Sex ChromosomesII. ANEUPLOIDY-an abnormal number of chromosomes.
A. This often results in genetic abnormalities.
B. Structural changes in chromosomes may lead to aneuploidy. Types of Structural Changes
include:
1. Deletions2. Duplications3. InversionsC. Nondisjunction-the failure of chromosomes to separate during meiosis. This is a major cause
of aneuploidy. This can occur in any set of chromosomes.
1. Example of Nondisjunction in Human Female Sex Chromosomes
2. Possible Outcomes of Female Nondisjunction.
a. Turner Syndrome-these individuals have the genotype XO.
1) How many chromosomes do these individuals contain?
2) These individuals are always short, sterile, ______________.
3) They do not go through puberty or menstruate.
4) They are usually of normal intelligence and lead normal lives.
5) Is often treated with hormone therapy.
b. Klinefelter Syndrome-the individual has the genotype XXY.
1) These individuals are always tall, sterile ___________.
2) They may exhibit some female secondary sex characteristics.
3) Mental retardation is a common characteristic of this syndrome.
4) They do lack facial hair and the testes are usually under developed.
c. Poly X Female-the individual has the genotype XXX.
1) In general, these individuals do not show any adverse signs or
symptoms. They are always _____________.
d. YO Zygotes-
3. Male nondisjunction can and does occur; however, it is usually much more severe than
nondisjunction in females. Usually, the offspring do not survive.
a. Sometimes in males, the Y chromosome can double itself leading to an XYY
individual. These are fertile males of normal appearance.
Some may experience severe acne. This is known as Jacob’s
syndrome.
4. Down Syndrome-occurs when there is an extra copy of chromosome #21. This is
caused by nondisjunction of an autosome.
a. Characteristics of Down Syndrome:
5. Unfortunately, none of the above illnesses can be cured.
III. CARRIERS-heterozygous individuals (Aa).
A. These individuals contain a detrimental, recessive allele. However, the carrier does
exhibit any symptoms of the recessive allele.
B. The carrier can pass the recessive allele on to their offspring. The offspring can
develop the illness if they are homozygous recessive.
IV. HUMAN GENETIC DISORDERS
A. Recessive Disorders-only occur in individuals with the genotype ______________.
1. Albinism-occurs when an individual lacks the gene that leads to the production
of melanin. What is melanin?
a. Characteristics of albinism
2. Cystic fibrosis (CF)-occurs when an individual produces extra supplies of
mucus in their lungs. The extra mucus can choke and kill the individual.
a. Males with CF can be sterile because the mucus can block the vas
defrens. Also, those with CF may not release sufficient supplies of
digestive enzymes since the pancreatic ducts can be blocked.
b. Currently, there is no cure for CF.
c. This is the most common genetic disorder among caucasians.
3. Sickle-cell anemia-occurs when an individual produces “sickle” shaped
red blood cells. Currently, there is no real cure for this illness.
a. What are red blood cells involved in?
b. Sickle shaped red blood cells do not carry oxygen efficiently.
c. Hemoglobin can also be damaged in this illness. What is hemoglobin?
d. Other signs and symptoms of this illness:
4. Tay-Sachs Disease-is a disease of the central nervous system.
a. In this disease, the individual lacks an enzyme needed to breakdown
lipids.
b. This disease is not treatable.
c. Signs and symptoms include:
5. Phenylketonuria (PKU)-occurs when the individual lacks the enzyme needed to
breakdown the amino acid phenylalanine.
a. This is most dangerous in young children.
b. This is treatable with diet and medication.
c. Many diet soft drinks contain warnings about the presence of
phenylalanine.
B. Dominant Genetic Disorders-occur in individuals that have a dangerous dominant
allele. What genotypes would individuals with these disorders have for a trait?
1. Polydactyly2. Huntington’s Disease
a. Symptoms of Huntington’s usually do not develop until the person
reaches their early 40’s. This disease is deadly.
3. Achondroplasia-rare form of dwarfism. Growth hormone production is shut
down by a defective gene in this disorder.
4. Hutchinson-Gilford Progeria-accelerated aging. Again this is very rare.
5. Osteogenesis imperfect-condition of weakened and brittle bones.
C. Sex-Linked Genetic Disorders-these are linked to a specific sex chromosome.
1. Hemophilia-is a recessive disorder that only appears in _____________.
a. What is hemophilia?
b. Where does the child get the allele for this illness?
2. Red-green color blindness
3. Male Pattern baldness
4. Muscular dystrophy
V. PEDIGREES
VI. HOW ARE GENETIC DISORDERS TREATED/CURED?
A. Most genetic disorders are untreatable and cannot be cured.
B. Some can be treated with medication or diet.
C. Currently, researchers are looking into the possibility of genetic engineering
as an answer.