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Unit 8 – Human Genetics Human Chromosomes ●Karyotype = picture of chromosomes arranged in pairs & organized by size ●Humans have 46 chromosomes ●2 of these are sex chromosomes XX = female XY = male ●The other 44 chromosomes are known as autosomes NONDISJUNCTION Failure of chromosomes to separate in meiosis – results in an egg (sperm) with too many or too few ●Down Syndrome (extra #21) ●Klinefelter Syndrome (XXY) ●Turner Syndrome (XO) ●Supermale (XYY) Down Syndrome - caused by an extra chromosome 21 (trisomy 21) Edward Syndrome - caused by an extra chromosome 18 (trisomy 18) Median life expectancy is 4 days. However, about 5-10% survive beyond one year Trisomy – 3 chromosomes Monosomy – 1 chromosome Checking in 1: 1. A picture of a person's chromosomes is called a _____. 2. In this pictures, chromosomes are arranged in pairs according to their ___________. 3. Humans have ______ pairs of chromosomes. 4. The last set of chromosomes is the _____ chromosomes. 5. Males have what sex chromosomes? ______ 6. A person who has an extra chromosome #21 has what disorder? __________ 7. If a person has XXY for sex chromosomes, he has what disorder? _________________ 8. As a woman gets _______, her risk for having a child with down syndrome increases. 9. A human has 2 sex chromosomes, the other 44 chromosomes are called ______________. 10. When chromosomes fail to separate during meiosis, ___________ has occurred. Human Traits ●To study inheritance, biologists use pedigree charts oShows relationships within a family Not all Human Traits can be traced back to a single gene Many traits are strongly influenced by environmental factors (ex: height, weight, personality) Human Genome ●Our complete set of genetic info ●Includes thousands of genes ●Base sequences of many genes identified BLOOD TYPES Genes controlling blood types were 1st genes to be identified ABO & Rh blood groups ( + and - ) ABO Blood Group Multiple Allele Trait ●Controlled by 3 alleles: A, B, O ●A and B are codominant ●O is recessive to both A and B ●The blood type is the phenotype Genotype Blood Type AA, AO Type A BB, BO Type B AB codominant Type AB (universal recipient) OO recessive Type O (universal donor) Blood Types Practice Mom has type A blood (genotype AO), dad has type AB blood. What blood types are possible among their children? Mom has type B blood (genotype BO), dad has type O blood. What blood types are possible among their children? Human Genetic Disorders Phenylketonuria (PKU) Tay – Sachs disease Albinism * all recessive Other animals can be albino too.. Sickle-Cell Disease codominant (AA, Aa, aa ) heterozygous is resistant to malaria Achondroplasia (dwarfism) Huntington’s disease * Both dominant Checking in 2: 1. Achondroplasia is another name for ____________ 2. What are the four possible blood types? _______ 3. Is albinism dominant or recessive? _________ 4. If two people are both heterozygous for sickle cell trait, what is the chance they they will have a child with sickle cell disease? 5. If a person with type A blood is married to person with type O blood, what blood types are possible in their children? 6. The human _______ describes all the genes found in humans. 7. What type of chart is used to study a trait in a family? __ Genes located on sex chromosomes follow different patterns of heredity. Males are more likely to be affected by these genes. ALL GENES ARE LOCATED ON CHROMOSOMES Some genes are located on the SEX CHROMOSOMES ( X and Y) Genes on the X chromosome may affect boys different from girls These are called SEX-LINKED GENES EXAMPLES: SEX LINKED GENES Coat color in cats: Black, Orange, Calico X B X B = black, female X O X O = orange, female X B X O = calico, female X B Y = black, male X O Y = orange, male REMEMBER: THE Y IS WIMPY! No letters (genes) are attached to it. CROSSES X B X B (black female) x This explains why all calico cats are female! ALSO: in any given cell, one of the X's becomes inactive, which randomizes the pattern or orange and black X OY (orange male) COLORBLINDNESS IS ALSO SEX LINKED Look what happens when a woman who is a CARRIER (b) marries a normal man (B) X BX b x XBY What happens when a colorblind man marries a normal woman? X BX B x XbY COLORBLIND TEST Young children are given pictures instead of numbers HEMOPHILIA - "bleeder's disease" Blood will not clot normally, small injuries can be life threatening Females can be carriers: What happens if Mom is a carrier? DUCHENNE MUSCULAR DYSTROPHY - causes progressive weakening and loss of muscle tissue Females can be carriers: X DX d Checking in 3: 1. Sex-linked genetic traits are on the _______ chromosome. 2. Are females or males more likely to be affected by a sexlinked traits? _______ 3. _________ can be carriers of sex-linked traits. 4. What are two examples of sex-linked traits?