1. The Human Genome

2. Gene Expression
Some of the most obvious human traits are not controlled by a single gene.
Some traits are polygenic
Environmental or nongenetic factors, including nutrition and exercise, strongly influence gene expression.

3. The Human Genome The human genome includes tens of thousands of genes.
By 2000, the DNA sequence of the human genome was almost complete.
Studying the human genome is difficult because we have:
long generation times
complex life cycles
few offspring

4. Blood Group Genes Best known are the ABO and Rh groups
Rh is controlled by a single gene.
The ABO blood group is controlled by multiple alleles. IA and IB are codominant.
Both determine blood type.
                                                     
              

5. Recessive Alleles
Many human genes became known through the study of genetic disorders.
Phenylketonuria (PKU) and Tay-Sachs disease are two examples of disorders caused by recessive alleles.

6. Recessive Alleles and Carriers
Someone who has only one recessive gene for a genetic disorder is called a carrier.
Because of recessive alleles, it is possible for two unaffected parents to have an affected child

7. Dominant and Codominant Alleles
Not all genetic disorders are caused by recessive alleles.
Huntington’s disease and achondroplasia, for example, are caused by dominant alleles.
Sickle cell disease is caused by a codominant allele.

8. From Gene to Molecule
Scientists are still working to understand many genetic disorders.
Cystic fibrosis and sickle cell disease are both caused by a change in the DNA of a single gene. This affects the structure of a protein which causes the disorder.

9. Cystic Fibrosis (CF)
Most common in people with Northern European ancestors.
Recessive disorder
Serious digestive problems
Thick, heavy mucus clogs lungs and breathing passages
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10. More on Cystic Fibrosis
Most cases of CF are caused by the deletion of 3 nucleotide bases.
One amino acid is deleted, and the protein is misfolded and destroyed.
Without the protein to allow chloride ions to pass through membranes, tissues in the body malfunction.

11. Sickle Cell Disease Most common in African Americans
Just one DNA base is changed
One amino acid is substituted
Abnormal hemoglobin is produced and the characteristic “sickle” shape results.

12. Why African Americans?
Malaria, a serious parasitic disease, is common in Africa.
Malaria infects red blood cells.
People who are heterozygous for the sickle cell allele are generally healthy and resistant to malaria.

13. Inheritance of Sickle Cell Disease

14. What makes us human? 46 chromosomes 44 autosomes
2 sex chromosomes (XX or XY)
A picture of chromosomes arranged in order is know as a karyotype.

15. Karyotype
A karytype can show extra or missing chromosomes, enlarged or shortened chromosomes.
It cannot show individual genes.

16. Nondisjunction
Every now and then the mechanisms that separate chromosomes during meiosis do not work properly.
This is called nondisjunction.
Abnormal numbers of chromosomes result.

17. Down’s Syndrome
                                                                                    
Down’s syndrome results from nondisjunction of the 21st chromosome.
1 baby in 800 in the U.S. has Down’s Syndrome
Mild to severe mental retardation as well as a susceptibility to disease and a higher incidence of birth defects results.

18. Sex Chromosome Disorders
Turner’s Syndrome
Nondisjunction results in only one X chromosome
Sterility results and sex organs do not develop at puberty
Klinefelter’s Syndrome
Nondisjunction results in an XXY genotype
Individuals are usually not able to reproduce
XXXY and XXXXY genotypes are also possible

19. Ya Gotta Have a Y to be a Guy!
No babies have ever been reported as born without an X chromosome.
The X chromosome contains gene necessary for survival.
The Y chromosome is responsible for male sex determination.
It can do this even if several X chromosomes are present.
                                                 

20. Human Moleculer Genetics
Biologists can now read, analyze, and even change the molecular code of genes.
They are able to search through the information in the humane genome using sequences of DNA bases.
A variety of genetic tests have been developed to spot these differences.

21. DNA Fingerprinting
Except for identical twins, no individual is exactly like another in terms of genetics.
DNA fingerprinting analyzes sections of DNA using restriction enzymes and gel electrophoresis.

22. More on DNA Fingerprinting
By comparing the bands of DNA, an individual can be identified.
DNA samples can be obtained from blood, sperm, and even hair strands if there is tissue at the base.

23. The Human Genome Project
In 1990, scientists in the United States and other countries began the Human Genome Project.
It is an ongoing effort to analyze the human DNA sequence.
In July 2000, scientists announced that a working copy of the human genome was essentially complete.

24. How Did They Do It? Some base sequences were used as markers.
“Shotgun sequencing” determined the sequence of fragments.
Fragments were put together like the pieces of a jigsaw puzzle.

25. Searching for Genes
Only a small part of a human DNA molecule is made up of genes.
One way scientists find genes is to search for DNA sequences known to be promoters.
A gene should be found behind each promoter.

26. Why Search For Genes?
The search for genes has both scientific and commercial value.
Genetic information may be useful in developing new drugs and treatment for diseases.

27.                               
Gene Therapy
Gene therapy is the process of changing a gene that causes a genetic disorder.
In gene therapy, an absent or faulty gene is replaced by a normal, working gene.

28. Putting Viruses To Work
Viruses are often used in gene therapy because of their ability to enter a cell’s DNA.
The DNA fragment containing the replacement gene is spliced to the viral DNA.
The virus injects the new gene into cells to correct genetic defects.

29. Ethical Issues In Human Genetics
As our knowledge increases, so does our ability to manipulate the genetics of living things, including ourselves.
Should science try to engineer taller people or change other characteristics?
Should we be able to design our babies?
What are the consequences of cloning?