Human Heredity

1. Human Heredity

2. Karyotypes • Genome= the full set of genetic information that an organism carries in its DNA • To see human chromosome, biologists photograph cells in mitosis (when chromosomes are fully condensed). They then cut them out and arrange them in a karyotype • a karyotype shows the complete diploid set of chromosomes grouped in pairs and arranged in order of decreasing size

3. Sex Chromosomes • First 44 chromosomes = autosomes • 2 of 46 chromosomes- sex chromosomes • Females: XX • Males: XY • X chromosome contains more than 1200 genes • Y chromosome contains about 140 • Most are associated with male sex determination and sperm development

4. Dominant and Recessive Alleles • MC1Rhelps determine skin and hair color • some of MC1R’s recessive alleles produce red hair • An individual with red hair usually has two of these recessive alleles (one from each parent) • Dominant alleles produce darker hair colors • Rh blood group- Rh+ and Rh- • Rh+ is dominant

5. Codominant and Multiple Alleles • ABO blood group determined by a gene with three alleles: IA, IB, and i • IA and IB are codominant—individuals with both alleles produce both antigens and therefore have the blood type AB • Homozygous recessive individuals (ii) produce no antigens and have blood type O

6. Sex Linked Inheritance • Hemophilia • Colorblindness

7. X- Chromosome Inactivation • In female cells, most of the genes in one of the X chromosomes are randomly switched off forming a dense region in the nucleus called a Barr body • Cats: the color of spots on their fur is controlled by a gene on the X chromosome. Spots are either orange or black depending on which X chromosome is inactivated in different patches of their skin. • Male cats can have spots of only one color • Tricolor  must be female

8. Human Pedigrees • A chart used to trace traits over several generations • Can be used for any species • Shows the presence or absence of a trait according to the relationships between parents, siblings, and offspring = FEMALE WITH TRAIT = FEMALE = MALE WITH TRAIT = MALE OR = DECEASED

9. More pedigree symbols… = MARRIAGE LINE = CHILD LINE

10. I 1 2 II 1 2 3 4 III 1 Generation# Individual #

11. I 1 2 II 1 2 3 4 III 1 • When describing a person you write the generation # a dash (-) then the individual number • Example: II-2 shows the trait • Example: II-1 is the oldest child of the original parents

12. I 1 2 II 1 2 3 4 III 1 This pedigree shows the occurrence of attached earlobes (shaded in). • What is the genotype of I-2? • What is the genotype of I-1? • Can II-1 be homozygous dominant? Earlobes E = Free earlobes e = attached earlobes

13. Human Genetic Disorders to know: • Sickle Cell Disease • Huntington’s Disease- caused by a dominant allele for a protein found in brain cells • symptoms: mental deterioration, uncontrollable movements • Appear in middle age • Cystic fibrosis (CF) • Most common in people of European ancestry • Deletion of 3 bases in the gene for a protein called CFTR removes phenylalanine from CFTR protein, causing protein to fold improperly • Cell membranes are unable to transport Cl- ions • CF allele is recessive • Children with CF have serious digestive problems and produce thick, heavy mucus that clogs their lungs and breathing passages

14. Genetic Disorders to know… • Tay-Sachs disease • Deadly disease of the nervous system • Autosomal recessive disorder • Common among Ashkenazi Jewish population • Symptoms appear between 3-6 months; child usually dies by age 4 or 5 • Symptoms: • Deafness, blindness • Loss of muscle strength, loss of motor skills • Increased startle reaction • seizures

15. Studying the Human Genome • For a long time, reading the DNA sequences in the human genome seemed impossible (the smallest chromosome contains nearly 50 million base pairs!) • 1960’s- scientists found that they could use natural enzymes in DNA analysis • By using tools that cut,separate, and then replicate DNA base by base, scientists can now read the base sequences in DNA from any cell

16. Cutting DNA • DNA is much too large to analyzed, so it must first be cut into pieces • Restriction enzymes= high specific substances produced by bacteria that can cut even the largest DNA molecule into precise pieces that are several hundred bases long • called restriction fragments • Hundreds of known restriction enzymes • A restriction enzyme is like a key that fits only one lock

17. Cutting DNA • The EcoRI restriction enzyme only recognizes the base sequence GAATTC. • Cuts each strand between G and A, leaving single-stranded overhangs with the sequence AATT • Overhangs called “sticky ends” because they can bond, or “stick” to a DNA fragment with the complementary base sequence

19. Separating DNA • Gel electrophoresis= a technique used to separate and analyze DNA fragments • DNA fragments are put into wells on a gel that is similar to a slice of gelatin • Electric voltage moves them across the gel (gel is positively charged on the end; fragments are negatively charged) • Shorter fragments move faster than longer fragments • Within an hour or two, the fragments separate, each appearing as a band on the gel

21. Reading DNA • After the DNA fragments have been separated, they are placed in a test tube containing DNA polymerase, along with all four nucleotide bases • DNA polymerase makes new strands of DNA using the templates • The researchers also add a small number of bases that have a chemical dye attached • Each time a dye-labeled nucleotide is added, DNA replication stops • The result is a series of color-coded DNA fragments of different lengths

22. Researchers can then separate these fragments, often by gel electrophoresis • The order of the colored bands on the gel tells the exact sequences of bases in the DNA • The entire process can be automated and controlled by computers so that thousands of bases can be read in a matter of seconds.

23. Genetic Engineering

24. Selective Breeding • Humans use selective breeding, which takes advantage of naturally occurring genetic variation, to pass wanted traits on to the next generation of organisms. • New varieties of plants (teosinte corn!!!) • Over 150 dog breeds • Horses, cats, and cows

25. Hybridization • Two common methods of selective breeding: • Hybridization • Inbreeding • Hybridization- crossing dissimilar individuals to bring together the best of both organisms • Hybrids- individuals produced by such crosses; tend to be hardier • Luther Burbank- developed over 800 varieties of plants • Combined disease resistance with food-producing capacity

26. Inbreeding • Inbreeding= the continued breeding of individuals with similar characteristics • Maintains desirable characteristics • Dogs • Can be risky—most of the members of the breed are genetically similar • Increases the chance that a cross between two individuals will bring together two recessive alleles for a genetic defect • Human example: Amish (Pennsylvania Dutch)—high incidence of genetic disorders since almost all descend from about 200 18th century founders

27. Increasing Variation • Breeders can increase genetic variation in a population by introducing mutations, which are the ultimate source of biological diversity. • Biotechnology= the application of a technological process, invention or method to living organisms • Manipulating the genetic makeup of an organism • Can increase mutations by exposure to radiation or chemicals • Can produce a few mutants w/ useful characteristics

28. Bacterial mutations • Millions of bacteria can be treated at one time increases chances of being successful • Allowed scientists to produce hundreds of useful bacterial strains • Oil-digesting bacteria for cleaning oil spills • Working on bacteria that can clean up radioactive substances and metal pollution • Polyploid plants • Use drugs that prevent that separation of chromosomes

29. Copying DNA • Extracting DNA- easy. • Finding a specific gene among millions of fragments- not so easy. • Southern blot analysis= a technique for finding specific DNA sequences, among dozens • Polymerase chain reaction (PCR)= a technique that allows biologists to make copies of a specific gene once it is found

30. PCR • A short piece of DNA that complements a portion of the sequence is added (called a primer) • DNA is heated to separate strands • As the DNA cools, primers bind to the single strands • DNA polymerase starts copying the region between the primers • These copies can sere as templates to make more copies

31. PCR

32. Recombinant DNA • A DNA sequence can be synthesized and incorporated into the DNA of an organism using DNA ligase or other enzymes • A gene from one organism can also be attached to the DNA of another organism…called recombinant DNA

34. Transgenic Organisms • Contain genes from other species • Produced by the insertion of recombinant DNA into the genome of a host organism • Can be done in plants and animals • Cloning

35. Genetically Modified (GM) organisms • GM crops- resistance to insects, herbicides, viral infections • Rot and spoilage??? • GM animals- 30% of milk in US comes from cows that have been injected with hormones that increase milk production • Pigs—more lean meat, high levels of omega-3 acids • Salmon– growth hormones • Spider genes in lactating goats—silk • Antibacterial goat milk

36. Recombinant DNA technology in health and medicine • Preventing disease • Medical research- simulate human disease in studies • Treating disease • HGH • Insulin • Blood clotting factors • Cancer fighting molecules (interleukin-2 and interferon)

37. Gene therapy • The process of changing a gene to treat a medical disease or disorder • An absent or faulty gene is replaced by a normal, working gene • Engineer a virus that cannot reproduce or cause harmful effects (just delivers the gene to the target cells) • Very high risk (Jessie Gelsinger)