3. What is a genome??? All the genetic information (genes) that make up an organism
4. What makes us human? Analyze human chromosome… Karotype Picture of all the chromosomes in an organism Autosomes CHROMOSOMES 1-44 (pairs 1-22) Autosomal chromsomes Sex chromosomes Determine a person’s sex (male XY or female XX) Chromosome 45 and 46 (set 23)
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6. Pedigree Charts Shows relationships within a family Genetic counselors use these to infer the genotypes of family members Look at each generation different symbols used
10. Recessive disorders Disorder phenylketonuria (PKU) Caused by an autosomal recessive allele on chromosome 12 People with this disorder lack the enzyme to break down phenylalanine (amino acid found in milk and many other foods) In newborns, this causes a build up of phenylalanine in tissues during the first few years of life and lead to mental retardation Newborns are commonly tested for PKU and then put on a low phenylalanine diet if they have the disorder
11. Autosomal Recessive Allele Tay-Sachs Disease Recessive allele in Jewish families of central and eastern Europe ancestry Lack the enzyme to break down lipids in neural cells Lipid accumulation in brain cells Leads to nervous system break-down and death in the first few years of life
12. Autosomal Recessive Disorders Cystic Fibrosis Do not have the gene that regulates mucus production Excess mucus in lungs, digestive tract, and liver Increased susceptibility to disorders Lung transplants usually needed after childhood
13. Autosomal Dominant Disorders You will express disorder if you are homozygous or heterozygous dominant for that trait You also have higher chances of passing onto your children Dwarfism (achondroplasia) Huntington’s Disease Nervous system disorder
14. Co-Dominant Alleles Disorders Sickle cell anemia 1/500 African Americans have the disorder Co-dominant allele Causes blockages in blood vessels, preventing oxygen from getting to other cells and tissues Beneficial in central and east Africa because it helped destroy malaria If you had SCA, your body would destroy the sickle cells to protect itself and in the process, destroy the malaria parasite as well
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16. Sex-Linked Disorders Many sex-linked genes are found on x-chromosome Many genetic disorders are sex-linked Males have just ONE x chromosome, so whatever the X chromosome is carrying (dominant or recessive) will be expressed Fathers can pass it to their daughters and the disorder can show up in the daughters sons
17. Sex-linked Disorders Red-green Color-blindness 1/10 men 1/100 women Hemophilia Two important genes on x-chr control blood clotting Person with disorder can die from minor cuts Recessive allele in either gene can cause it Duchenne Muscular Dystrophy Caused by defective version of a gene for a muscle protein Progressive weakening and loss of skeletal muscle1/3000 males
18. X-chromosome Inactivation Females have XX and males have XY…is the second X chr in females needed?? British Geneticist Mary Lyon In female cells, one x-chromosome is randomly shut off…this “shut off” chromosome is called a Barr Body Different X-chrm are switched off in different cells Generally not found in males b/c X-chrm needs to be ACTIVE Occurs in other mammals as well
19. Barr bodies in cats Gene that controls color of coat spots is located on the X-chrm In a female, one X-chrm may have the allele for orange spots and the other X-chrm may have the allele for black spots Different cells in different parts of the cat’s body are switched off= different colored spots on different parts of the cat…mix or orange and black spots Males only have ONE active X-chrm…therefore, will they have different colored spots? No…only psots of ONE color (b/c on ONE active X) This is one way to determine the sex of a cat…cat with black AND orange spots is almost always certainly female
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21. Chromosomal Disorders Mechanics of meiosis (where we separate chromosomes) is usually pretty good But nobody’s perfect…mistakes happen…. Most common problem… Nondisjunction: when homologous chromosomes fail to separate properly Literally means “not coming apart” If this occurs, ABNORMAL #s of chromosomes may find their way into gametes and a disorder of chromosome number may result
22. Nondisjunction If one of the gametes with an ABNORMAL # ends up getting fertilized, MAJOR problems!!! Trisomy: “three bodies” Occurs when an autosomal chromosome fails to separate during meiosis When do chrm separate? Anaphase I and Anaphase 2 One gamete ends up with an extra copy of a chromosome and then the fertilized zygote ends up with 3 copies of a chrm instead of 2 Example: Downs Syndrome
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25. Down Syndrome Extra copy of chromosome 21 1/800 baby’s are born with this disorder Produces mild to severe retardation Increased susceptibility to diseases, slower development, and higher frequency of birth defects How can one little extra copy cause so many problems? Scientists are still trying to figure that out…now that they have used gene mapping and identified all the genes on chromosome 21, they can begin experimenting on this problem
26. Sex Chromosome Disorders What happens if nondisjunction happens to the sex chromosomes??? We know we need at least one X chromosome…. No embryos have been found with just a Y chromosome so we now X chrm contains vital genes! Turners Syndrome Females receive only one X chromosome Karotype 45, X Unable to reproduce, sex organs do not develop at puberty Klinefelters Syndrome Males receive an extra X chromosome Karotype 47, XXY Prevents individuals from reproducing Cases of individuals with XXXY and XXXXY Y chromosome contains “sex determining region” SDR, which gives male characteristics and development If region is absent, embryo develops into female
29. What about an extra Y? Males with 47, XYY produce more male hormones and express a more expressive behavior More testosterone=more aggressive behavior Higher number of men in prison for violent crimes have XYY however there is a large population of men with XYY that do not exhibit (or at least act upon) this aggression Cannot use this as an excuse for aggressive behavior or else criminals would be pleading an extra Y instead of insanity :-o
