Karyotype and Genetic Disorders
Human Genome Project
- 13 year project to identify all 20,000
genes for a human
- know the sequence of 3 billion base pairs
- store the information in a database
- address the ethical questions of gene
identification and gene therapy
- completed in 2003
Karyotype- Picture of arranged chromosomes
- Humans have 23 pairs of homologous
chromosomes (22 autosomal pairs)
- Homologous= each similar in size and shape
- Process= Scientists take a picture of cells during mitosis, cut out
chromosomes, and group in pairs according to size and centromere
location
- Uses= See the number of chromosomes and identify genetic disorders
Chromosome Map
- the picture of a chromosome with genes labeled
- Loci= the location of a gene on a particular chromosome
Huntington Disease
Genetic Disorders
Disorders caused by Recessive Allele:
1. PKU= Phenylketonuria
- People with PKU lack the enzyme needed to break down
phenylalanine (amino acid found in milk), so it builds up in tissues
- May cause mental retardation
- Babies are tested to prevent effects
2. Tay Sachs
- Buildup of lipids in brain cells
- Causes a break down of the nervous system and blindness
- Leads to death in early childhood
3. CF= Cystic Fibrosis
- Caused by deletion of 3 bases in DNA
- Results in digestive problems and mucus buildup in lungs
Disorders caused by Dominant Allele:
1. Huntington disease
- Loss of muscle control and mental function
- Symptoms appear middle age (30+)
Disorders caused by Codominant Alleles:
1. Sickle Cell
- Common in African Americans
- Results in bent and twisted red blood cells, causing
them to get stuck in the capillaries (tiny blood vessels)
- Physical weakness; damage to brain, heart, and other organs
- Heterozygous are healthy and resistant to malaria
- One DNA base is substituted resulting in the hemoglobin having a
different sequence of amino acids
Chromosomal Disorders
Nondisjunction- homologous chromosomes fail to separate during meiosis
- Can occur with autosomal and sex chromosomes
- Causing abnormal number of chromosomes
- Causing disorders, such as:
1. Down Syndrome
- 3 copies of chromosome 21 (trisomy)
- People with Down Syndrome share common physical traits, such as
flat facial profile, small ears, and an upward slant in the eyes
- Causes mild to moderate mental retardation and developmental delays
- Effects 1 out of every 800 babies
- Risk of conceiving child with Down Syndrome increases with the
mother’s age.
2. Turner’s Syndrome
- Only one X chromosome= X or XO
- Sterile female
3. Klinefelter’s Syndrome
- XXY= male
- No documented cases of person born without an X chromosome
because it is needed for normal development.