Transcript PPT File
HUMAN GENETICS Pedigree • A graphic representation of genetic inheritance. • Looks like a family tree. Analyzing a pedigree Is the trait you are analyzing a recessive or dominate trait? What are the genotypes of parents I1, I2? What is the probability of II-4, II-5 being a carrier? What is the genotype of individual II-2? What is individual III-1 chance of being a carrier? Simple recessive heredity • Most genetic disorders are caused by recessive alleles. • It require both recessive alleles to manifest the trait. • Do problem solving lab 12.1 page 317. Cystic fibrosis • Most common genetic disorder among white Americans. • 1in 20 is a carrier • 1in 2000 are born with the disease. • Defective protein in the plasma membrane. • Results in accumulation of thick mucus in the lungs and digestive tract. • Usually Fatal before 35. Tay-Sachs Disease • Affects the central nervous system(CNS). • Results in the absence of an enzyme that normally breaks down a lipid produced and stored in tissues of the CNS. • . • The lipid accumulates in the cells, causing a lack of coordination and eventually chokes off the nerves. This results in the death of the individual over a period of 1-2 years • Common in the U.S. among the Amish and Ashkenazic Jews. Phenylketonuria (PKU) • Absence of one amino acid that converts phenylalanine to tyrosine. • The phenylalanine accumulates in the body and results in severe damage to the CNS. • PKU newborns appear normal. • Once the infant begins to drink milk (high in phenylalanine) the amino acid accumulates causing mental retardation. • PKU is normally tested for right after birth, and given a diet low in phenylalanine, until their brains are fully developed. Dominant heredity • Most dominant traits are non lethal. • Since only one allele is needed to express the trait, they are very common. • Tongue rolling • Freely hanging earlobes • Protruding bottom lip • Hitchhikers thumb Huntington’s Disease • Lethal disease that is very rare. • Results in a breakdown of the brain. • No effective treatment. • Normally dominant lethal diseases result in the death of the zygote. • Huntington’s strikes between the ages of 30 to 50. Complex Patterns of Inheritance • Not all patterns of inheritance follow Mendel’s simple patterns. Incomplete dominance • When the phenotype of a heterozygote is intermediate between those of the two homozygotes. • Chinese Snap Dragon • RR = red, RR’ = Pink, R’R’= White Codominance • Where more than one allele is dominant for a single trait. • B = black, W = white • BW = Black & white WW = White BB = Black BW = Black & White Codominance in Humans • Sickle-cell anemia • Major health problem in the U.S. and Africa. • Common among Blacks, and whites who originated around the Mediterranean Sea. • 1 in 12 African Americans is heterozygous for the disorder. • 1 Amino acid is different in hemoglobin. • Causes the red blood cells to turn sickle shaped. • Individuals who are Homozygous dominant suffer greatly • Heterozygous individuals produce normal and sickle shaped hemoglobin. They can live a somewhat normal life. • HbA = Normal hemoglobin • HbS = Sickled hemoglobin • HbA HbA = Normal • HbA HbS = Heterozygous (both normal and sickled) • HbS HbS = Sickled (sickled only) Multiple Alleles • Traits controlled by more than two alleles. • Sometimes there are more than two alleles that code for a single trait, however, any one individual can only have two alleles. • In pigeons a single gene controls feather color. There are 3 alleles for feather color. • BA = ash red feathers • b = chocolate feathers • B = Blue feathers • b is recessive • B is dominant to b but recessive to BA • BA is dominant over both B and b. A A B B , A B B, A B b BB,Bb bb • You have been given some baby pigeons. One Blue, one chocolate, and one ash red. You were told that the babies were all from the same parents. Is this possible? If so prove it using a Punnett square Multiple Alleles in Humans • Human blood has three alleles. • A, B, and O. • You can only have 2 of the alleles. • Possible Human Blood types • AA, AO = phenotype A • BB, BO = phenotype B • AB = phenotype AB • OO = Phenotype O • Do the blood type handout. Sex determination • Humans have 23 pair of chromosomes, the 1st 22 pair of chromosomes are called autosomes. • The last pair of chromosomes are the sex chromosomes. • The sex chromosomes determine the sex of the individual. • Females have XX as their 23rd pair of chromosomes. • Males have XY as their 23rd pair of chromosomes. • See Punnett square on board. Sex linked inheritance • Traits found on the sex chromosomes are said to be sex linked. • Traits found only on the Y chromosome of the male have no corresponding alleles on the X chromosome. Thomas Hunt Morgan • In 1910 was working with fruit flies. • He noticed that a male fly had white eyes instead of normal red. • After breeding many flies, he noticed that only males would have white eyes. • See Punnett squares on board. RED GREEN Color Blindness • Located on the X chromosome. • Recessive trait. • XCY = normal male • XcY = color blind male • XcXc = Color blind female C c X X = normal female carrier C C X X = normal female Hemophilia • X linked disorder. • Blood clotting factors missing • 1 male in 10,000 • 1 female in 100,000,000 • WHY???????????!!!!?!?!?!? • Single recessive allele on the X chromosome is response able. • XhXh = Hemophilia in females • XHXh - female carrier H H • X X = female normal • XHY = normal male • XhY = hemophilic male Polygenic inheritance • Traits governed by many different genes. • Skin color, height, corn cob length. • Results in a wide range of variability. • Genes may be on the same or different chromosomes. 25 20 15 10 5 0 4cm 6cm 8cm 10cm 12cm 14cm 16cm Environmental influences • The genetic make up of an organism at fertilization determines only the organism’s potential to develop. • Many things influence the development of an organism. External environment. • Temperature • Light • Chemicals • Infectious agents • ETC. Internal environment. • Hormones cause: • Male pattern baldness (Humans) • Feather color (Peacocks) • AGE: causes genes to not function properly. Changes in Chromosome # • During Metaphase I or II nondisjunction causes abnormal amounts of chromosomes. • Individuals who suspect they might have a abnormal fetus can have a karyotype done. Karyotype • A procedure where the chromosomes are obtained, photographed and arranged in homologous pairs. • Used to look for any abnormalities. Extra autosomes • Down syndrome - extra chromosome 21 Unusual numbers of sex chromosomes • XO - Missing X chromosome (turners syndrome. 1 in 2500 females. Live normal, but are sterile. • XXX - triple X syndrome. 1 in 1200 females. Live a normal life. • XXY - Klinefelter’s syndrome. 1 in 400 males. Results in sterility. Otherwise normal. • XYY - XYY syndrome. 1 in 500 males. Usually normal. Might be taller. • Do Section Assessment 12.3 page 335.