2. Karyotype - Set of photographs of chromosomes grouped in order in pairs. Cell biologists photograph cells in mitosis when the chromosomes are fully condensed and easy to see. Then the chromosomes are cut from the photographs and grouped together in pairs.

3. Remember: Different species have different chromosome numbers. Humans have 46 chromosomes. Human gametes (sex cells) contain 23 chromosomes. Human somatic (body) cells contain 46 chromosomes.

4. Autosomal Chromosome- Chromosome that is not a sex chromosome Sex Chromosome – Two of the 46 chromosomes that determine an organisms sex. Sex Chromosomes

5. Females: Have two X chromosomes (XX) Males: Have one X chromosome and one Y chromosome (XY) Males and females are born in a 50:50 ratio because of the way in which sex chromosomes segregate in meiosis. 50% chance of being a male or female!

6. Pedigree Chart - Chart that shows the relationships within a family Tool for tracing a trait through generations of a family. Used to predict whether a person is a carrier of a heredity disease.

7. Some of the most obvious human traits are almost impossible to associate with single genes. Two reasons why: 1. Things you might think of as single traits (such as the shape of your eyes or ears) are actually controlled by many genes. 2. Many of your personal traits are only partly governed by genetics. Many traits are strongly influenced by environmental factors, including nutrition and exercise. Example: Nutritional improvements in the US and Europe have increased the average height of these populations about 10 cm. over their average height in the 1800s.

8. Write down how you would analyze the pattern in the inheritance of the albinism trait. Describe how you will use your analysis to infer the genotype of as many individuals as possible.

9. Human Genome - Our complete set of genetic information. Includes tens of thousands of genes. By 2000, the DNA sequence of the human genome was almost complete. Biologists were able to identify genes that directly control a single human trait.

10. Many disorders are caused by recessive alleles. Examples include: 1. Albinism 2. Cystic fibrosis 3. Tay-Sachs disease

11. Some genetic disorders are caused by dominant alleles. If you have a dominant allele for a genetic disorder, it will be expressed (even if the recessive allele is present). Examples include: 1. Achondroplasia (Dwarfism) 2. Huntington’s Disease (nervous system disorder) 3. Hypercholesterolemia (excess cholesterol in blood)

12. Disease is caused by a recessive allele on chromosome 7. Symptoms: Serious digestive problems Production of a thick, heavy mucus that clogs lungs and breathing passageways. Involves a very small genetic change Caused by the deletion of 3 bases in the middle of a sequence for a protein. 1. Removes just one amino acid from this large protein, causing it to fold improperly. 2. The cells are unable to transport the protein to the cell membrane and the protein is destroyed. 3. Unable to transport chloride ions, tissues throughout the body malfunction

13. Sickle cell disease is characterized by the bent and twisted shape of the red blood cells. Are more rigid than normal cells and tend to get stuck in the capillaries. Blood stops moving through these vessels, damaging cells, tissues, and organs. Produces physical weakness and damage to the brain, heart, and spleen. May be fatal. Caused by: Just one DNA base is changed. This change substitutes the amino acid valine for glutamic acid.

14. Genes located close together on the same chromosome are linked, meaning that they tend to be inherited together. Genes located on the sex chromosomes are said to be sex-linked genes. More than 100 sex-linked genetic disorders have now been mapped to the X chromosome. The human Y chromosome is much smaller than the X chromosome and appears to contain only a few genes.

15. Males have just one X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive. In order for a recessive allele to be expressed in females, there must be two copies of the allele (one on each of the two X chromosomes). Example – Colorblindness Genes associated with color vision are located on the X chromosome. Males: Found in about 1 in 10 males in the US. A defective version of any one of these genes produces colorblindness Females: Found in about 1 in 100 females (rare).

16. 1. Colorblindness 2. Hemophilia About 1 in 10,000 males is born with a form of hemophilia. 3. Duchenne Muscular Dystrophy 1 out of every 3000 males is born with this condition.

17. The most common error in meiosis occurs when homologous chromosomes fail to separate. This is known as nondisjunction, which means “not coming apart.” If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result.

18. May be born with three copies of a chromosome (known as a trisomy) Most common form involves 3 copies of chromosome 21. About 1 baby in 800 is born with Down syndrome. Symptoms: 1. Mild to severe mental retardation 2. Increased susceptibility to many diseases 3. Higher frequency of some birth defects.

19. The roughly 6 billion base pairs you carry in your DNA are a bit like an encyclopedia with thousands of volumes. You find a way to look up only what you need. In an encyclopedia, you can use an index or an alphabetical list of articles. Biologists search the volumes of the human genome using sequences of DNA bases.

20. Because genetic disorders have slightly different DNA sequences from their normal counterparts, a variety of genetic tests have been developed that can spot those differences. 1. Use labeled DNA probes which are specific DNA base sequences that detect the complementary base sequences found in disease-causing alleles. 2. Other tests search for changes in restriction enzyme cutting sites. 3. Tests also detect differences between the lengths of normal and abnormal alleles.

21. Genetic tests are now available for hundreds of disorders. Making it possible to determine whether prospective parents risk passing such alleles to their children. DNA testing can pinpoint the exact genetic basis of a disorder, making it possible to develop more effective treatment for individuals affected by genetic disease.

22. DNA fingerprinting - Analysis of sections of DNA that have little or no known function, but vary widely from one individual to another, in order to identify individuals. Does not analyze the cell's most important genes, which are largely identical among most people. DNA samples can be obtained from blood, sperm, and even hair strands with tissue at the base. Has helped convict criminals as well as overturn many convictions

23. 1. Small sample of human DNA is cut with a restriction enzyme. 2. The resulting fragments are separated by size using gel electrophoresis. 3. Fragments containing these highly variable regions are then detected with a DNA probe, revealing a series of DNA bands of various sizes. 4. A pattern of bands is produced that can be distinguished statistically from the pattern of any other individual in the world.

24. In gene therapy, an absent or faulty gene is replaced by a normal, working gene. First authorized attempt to cure a human genetic disorder by gene transfer occurred in 1990. In 1999, a young French girl was cured of an inherited immune disorder when cells from her bone marrow were removed, modified in the laboratory, and then placed back in her body.

25. Viruses are often used because of their ability to enter a cell's DNA. 1. The virus particles are modified so that they cannot cause disease. 2. Then, a DNA fragment containing a replacement gene is spliced to viral DNA. 3. The patient is then infected with the modified virus particles, which should carry the gene into cells to correct genetic defects.

26. Unfortunately, gene therapy experiments have not always been successful. Attempts to treat cystic fibrosis by spraying genetically engineered viruses into the breathing passages have not produced a lasting cure. For all the promise it holds, in most cases gene therapy remains a high-risk, experimental procedure.

27. Recombinant DNA - DNA produced by combining DNA from different sources “Synthetic” DNA sequences can be joined to “natural” ones using enzymes. Is possible to take a gene from one organism and attach it to the DNA of another organism by using enzymes.

28. During transformation, a cell takes in DNA from outside the cell. This external DNA becomes a component of the cell's DNA. Griffith mixed heat-killed bacteria with live bacteria and a few of them actually took up the DNA molecules. Bacteria can be transformed simply by placing them in a solution containing DNA molecules.