1. CHAPTER 14 THE HUMAN GENOME

2. Human Heredity INTRODUCTION
Humans have 46 chromosomes made of DNA & protein
autosomes – 44 of the 46
sex chromosomes – either XX (female) or XY (male).
eggs carry only X chromosome.
½ of sperm carry X
½ of sperm carry Y

3. Human Heredity Karyotype
Photograph of chromosomes of cells during mitosis.
Amniocentisis – how cells are gotten for a karyotype.
Long needle is inserted right into where the baby is developing (amniotic sac).
Done between weeks of pregnancy
SEE FIG. 14-1, pg karyotype of a male.
Used to see if there is a chromosomal disorder in a baby.
Can detect disorders like Down’s Syndrome, Kleinfelter’s Syndrome, Turner’s Syndrome.

4. Human Traits
Scientists try to identify inherited traits controlled by one gene.
Must make sure the trait is controlled by the gene and not influenced by the environment.
Pedigree – a chart used to study how a trait is passed from one generation to another in a family.
Fig. 14-3
Carrier – an individual who carries one allele for a trait and is not affected by that gene.

5. Human Traits Cont’d
Impossible (almost) to associate one gene with one trait for two reasons:
Polygenic – controlled by many genes.
Shape of eyes, ears, hair color, etc.
Environmental influence.
Nutrition, exercise.
Height – determined by genetic factors, but strongly influenced by environment (nutrition, etc.)
Today, humans are approx. 10cm taller than in the 1800’s.
Even though environment influences genes, that does not mean that those genes can’t reach their full expression in future generations.

6. Human Genes DNA sequence determines characteristics
Sequence of nucleotides
Studying is difficult because:
Length between generations
Very few offspring are produced.

7. Human Genes Cont’d ABO blood group
3 alleles for this gene – IA, IB and I
IA & IB are codominant
i is recessive.
alleles produce antigens
immune system recognizes giving the “blood type”.
IAi - Blood type “A”
IBi – Blood type “B”
IAIB – Blood type “AB”
ii – Blood type “O”
SEE FIG 14-5, pg. 344

8. Rh FACTOR + or – part of a person’s blood type.
found through the rhesus monkey
single gene with two alleles (+ or -)
Rh+ is dominant
Rh- is recessive.
RHESUS MONKEY

9. RECESSIVE GENETIC DISORDERS PKU – PHENYLKENTONURIA
lack enzyme to breakdown amino acid phenylalanine.
found in foods like, milk, sugar substitutes, etc.
builds up and causes mental retardation.
A diet low in phenylalanine will prevent the effects
All newborns are tested for this.
allele is found on chromosome 12.

10. TAY-SACH’S DISEASE
Found mostly in people of Jewish descent from central and eastern Europe.
Enzyme lacking that breaksdown lipids in the brain.
Children die within 5 – 7 years of life.
No treatment
Can learn the probability of having a child with the disorder by genetic testing.
Recessive disorder.

11. DOMINANT DISORDERS Expressed no matter what
only need one copy of the gene.
Achondroplasia
form of dwarfism
Huntington’s Disease
progressive loss of muscle control and mental function.
No symptoms until middle age.

12. DISORDERS CAUSED BYCHANGES IN THE DNA SEQUENCE.
Sickle – Cell Disease
Causes the red blood cells to turn into a “sickle” shape.
Blood cells can’t fit through the small vessels.
Causes pain.
Affects 1 in 500 African Americans .

13. CYSTIC FIBROSIS (CF) Most common in Northern Europe descendents.
Patients now live past their 20’s.
Caused by the deletion of 3 bases
1 amino acid
Causes the protein to fold incorrectly and it is destroyed.
The malfunction of the protein does not allow chloride ions to move across membranes.
Over production of mucous
Serious problems in the digestive system and lungs.
It is a recessive disorder.

14. SEX-LINKED DISORDERS
More than 100 sex-linked disorders mapped to the X chromosome.
Males only receive one X, so they are more susceptible to sex-linked disorders.
Males pass defective X chromosome to their daughters who are then “carriers” and can pass it to their sons.
Seems to “skip a generation”

15. COLOR-BLINDNESS
3 genes on the X chromosome responsible for seeing in color.
Defect in any of the 3, results in some form of colorblindness.
Most common
red-green – can’t see red and green.
Found in 1 of 10 males in the US
Females need 2 defective X chromosomes to be colorblind
only 1 in 100 in US.

16. Hemophilia
x-linked disorder where the protein that makes blood clot is missing.
Patients can bleed to death from a simple cut or bruise.
2 genes control blood clotting on the X chromosome.
Defect in either gene results in hemophilia.
Affects 1 in 10,000 males
Coagulation Factor VIII

17. Duchenne Muscular Dystrophy
x-linked disorder where there is a weakening of muscles.
Patients rarely live into adulthood.
Defect in the gene on the X-chromosome that codes for muscle protein.
1 in 3,000 males is affected in the US

18. Chromosomal Disorders (whole chromosome)
Down Syndrome – autosomal genetic disorder caused by nondisjunction of chromosome # 21.
Trisomy – three copies of one chromosome
Most common form of trisomy – 3 copies of chromosome #21.
Causes mild to severe mental retardation
Patients are usually sterile
characterized by an asian-looking face.
Usually die of heart problems in their 40’s.
See. Fig , pg. 353.

19. Turner’s syndrome Nondisjunction of the X chromosome.
Females only have one X chromosome XO
Females are sterile and very short, but otherwise are normal females.

20. Kleinfelter’s syndrome
Nondisjunction of the X chromosome
Males are XXY.
Males are sterile and suffer from mental retardation.

21. Human Molecular Genetics
Human DNA Analysis
6 billion base pairs in the DNA sequence.
Biologist search the genome using base pair sequence in the DNA .

22. Testing for Alleles Can label DNA to see specific sequences.
This can test parents to see if they are a carrier for a genetic disorder like cystic fibrosis or Tay-Sach’s.
Done using small fragments of DNA & checking the length of the fragments.
Use restriction enzymes to cut the DNA into fragments.

23. Testing for Alleles
Used to identify an individual because no two organims share the exact same DNA (except identical twins)
DNA is cut with restriction enzymes into fragments.
Fragments are separated by their size using gel electrophoresis.

24. DNA Fingerprinting
Some fragments show great differences (variability) and are detected using a DNA probe.
Called “restriction length polymorphisms” or RFLP
fragments separate and create bands that can be read by scientists and identify an individual.
Samples of DNA can be gotten from blood, hair, sperm, skin, etc.
See Fig , pg. 356

25. The Human Genome Project
Dr. James Watson & Dr. Francis Collins – begun in 1990
Wanted to map the entire human genome.
1996- E. coli was mapped.
2000 – Sequencing of the human genome was completed.
Contains between 31,000 – 37,000 genes.

26. The Human Genome Project
This information could one day be used:
commercially;
biotechnology could provide:
new drugs
treatments for disease based on a person’s genetic code.

27. Gene Therapy Absent or abnromal gene is replaced by a normal gene.
Correct the protein or enzyme
1999 – French girl was “cured” of a genetic immune disease
“Changed” her bone marrow cells and then placing them back into her body.

28. Gene Therapy Viruses are used to modify genes.
Incorporate their DNA into a host’s DNA.
Cannot cause disease.
The correct gene is spliced into the virus’s DNA
The “corrected” gene is put into the patient
Incorporated into the DNA, correcting the protein/enzyme.
Still very experimental and has not had much success yet.

29. Ethical Issues in Human Genetics
Questions as to how genetic information should be used:
Who should have access to your genetic information?
Should humans be “designed”?
Should information on the probability of a person getting a disease (ex. Heart disease) be shared with insurance companies or employers?
Should any person arrested for any reason have to submitted a sample of their DNA for use in a criminal library?
This is already being done.