* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Inheritance Patterns & Human Genetics
Gene expression programming wikipedia , lookup
Genetic code wikipedia , lookup
Cell-free fetal DNA wikipedia , lookup
Saethre–Chotzen syndrome wikipedia , lookup
Behavioural genetics wikipedia , lookup
Frameshift mutation wikipedia , lookup
Genetic drift wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Genomic imprinting wikipedia , lookup
Population genetics wikipedia , lookup
DiGeorge syndrome wikipedia , lookup
Medical genetics wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Designer baby wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Point mutation wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Microevolution wikipedia , lookup
Down syndrome wikipedia , lookup
Genome (book) wikipedia , lookup
Y chromosome wikipedia , lookup
Inheritance Patterns & Human Genetics Chapter 12 Topics: 12-1 Chromosomes & Inheritance 12-2 Human Genetics Honors/CPI 1 Sex Determination Thomas Morgan, Columbia University, first identified the “X” & “Y” chromosome He studied the fruit fly, Drosophila, which has 4 homologous pairs of chromosomes He found that one set of chromosomes in females looked the same, while in males one was smaller He surmised (correctly) that these controlled the sex of the individual He labeled the female XX & the male XY During meiosis, the gametes formed contain either an X or a Y chromosome Thus the resulting zygote will be XX or XY 2 Sex Linkage Genes are located on sex chromosomes are sexlinked genes Some are X-linked genes Some are Y-linked genes In Drosophila, eye color is sex-linked Morgan found females had red eyes, but some males had white eyes. Why are there no white-eyed females? Morgan crossed a red-eyed female with a white-eyed male Result: F1 100% Red-eyed Crossed F1 Result: F2 75% Red-eyed, 25% White-eyed (males) 3 Assume: eye color linked to X chromosome R – dominant allele (red eye) r – recessive allele (white eye) XrY Male Parent XRXR Female Parent F1 Xr XR XRXr XRY XR XRXr XRY Y XRY Male Parent XRXr Female Parent F2 XR Y XR XRXR XRY Xr XRXr XrY So, why are there no white-eyed females? 4 Linkage Groups Chromosomes contain thousands of genes Genes located on one chromosome form a linkage group and tend to be inherited together In Drosophila, grey body color dominant to black body color & long wings are dominant to short wings; these form a linkage group and so they are passed together to gametes Crossing-over can occur during meiosis I Exchange of genes between homologous pairs So, this disrupts linkage groups and introduces a rearrangement of the genes in gametes 5 Mutation – change in the nucleotide sequence of DNA Germ cell mutations – affect the gametes Somatic cell mutations – affect organism’s cells, can disrupt/affect cellular activities, often resulting in cancers Cannot affect cellular activities of organism Cannot be passed to offspring Lethal mutations – result in death, often prior to birth Some mutations are beneficial enabling organism’s phenotype to be enhanced in some way 6 Mutation Types Deletion – a change in chromosome structure or a loss of part of a chromosome Inversion – a segment breaks off & reattaches in reverse orientation Translocation – a segment breaks off & reattaches to another chromosome Nondisjunction – failure of homologues to separate during meiosis, one gamete gets an extra while other gamete gets none or some portion of a homologue Point Mutation – substitution, addition, or removal of a nucleotide Substitutions – one nucleotide in a codon is replaced by a different nucleotide resulting in a new codon; this changes amino acid for which it codes 7 Sickle-Cell Anemia Substitution Point Mutation Adenine is substituted for thymine of 1 codon DNA mRNA Amino Acid Normal CTT GAA Glutamic Acid Point Mutation CAT GUA Valine This amino acid important to formation of hemoglobin molecule Heterozygous individuals have one allele with the point mutation; sickle cell trait Homozygous recessive individuals have 2 alleles with the point mutation; sickle cell anemia Sickle cell trait results in normal & abnormal RBCs In US, 1 in 10 Americans of African descent are carriers Sickle cell anemia results in abnormal RBCs; causes intense pain, tissue damage, death In US, 1 in 500 Americans of African descent are afflicted 8 Pedigrees “A Family Tree” Punnett squares are helpful, but provide only information on one generation at a time Pedigree analysis provides a pattern of inheritance within a family grouping Phenotypes of family members are studied Rules for making a pedigree Circles are females; squares are males If circle/box is cut in ½ individual is heterozygous Horizontal lines represent marriage unions or linkage between brothers & sisters Vertical lines represent offspring; offspring in order LR oldestyoungest; birth/death dates often included 9 Hemophilia “The Royal Disease” 10 Hemophelia: X-linked Inheritance Pattern The incidence of hemophilia is about 1:7,500 live male births and 1:25,000,000 live female births. There are about 17,000 people living with hemophilia in the United States. As many as 1/3 of the people with hemophilia may have gotten it from a spontaneous mutation of the factor VIII clotting gene on their X-chromosome. The full blown version of factor VIII deficiency is very rare in women; resulting from having an affected father and carrier mother 11 Genetic Traits & Disorders Single Allele Traits: traits determined by a single allele Multiple Allele Traits: traits determined by many alleles Polygenic Traits: traits determined by more than one gene X-Linked Traits: traits coded for on the X chromosome that have no allele counterpart on the Y chromosome Sex-Influenced Traits: traits whose expression is influenced by sex hormones 12 Human conditions/diseases Single allele traits (dominant) Single allele traits (recessive) Hair/skin/eye color, foot size, nose length, height X-linked traits Albinism, cystic fibrosis, phenylketounria, hereditary deafness Polygenic traits Huntington’s disease, dwarfism, cataracts, polydactyly Colorblindness, hemophilia, muscular dystrophy, icthyosis simplex Multiple allele traits ABO blood groups 13 ABO Blood Groups Three alleles control blood type: IA, IB, i Blood types are: A, B, or O Genotype Blood Type IAIA A IAi A IBIB B IBi IAIB ii B AB O 14 Human Genetic Disorders Genetic screening Genetic counseling Test amnionic fluid for genetic defects, protein defects, karyotype Chorionic Villus Sampling (wk 8-10) Counseling on test results, options Amniocentesis Examine pedigrees, genetic tests Test chorion villus for genetic defects, karyotype Post-birth tests PKU http://en.wikipedia.org/wiki/Phenylketonuria 15 Disorders Due to Nondisjunction Nondisjunction occurs during meiosis I resulting in gametes getting no chromosome, an extra chromosome or a partial piece of a chromosome Resultant conditions termed: Monosomy – condition in which the human zygote has only 45 chromosomes Trisomy – conditions in which the human zygote has an extra chromosome, ie., 47. Sometimes an entire or just a portion of a chromosome is extra in the genotype These disorders may happen to either the autosomes or sex chromosomes Autosomal monosomies: all lethal, fetuses spontaneously abort prior to birth http://anthro.palomar.edu/abnormal/abnormal_4.htm Autosomal trisomies: most lethal; only trisomy of chromosomes # 13, 18, 21 can result in a live birth. 16 Autosomal Trisomies: Trisomy 13 – Patau Syndrome (1 in 8-12,000 births US); survival after birth ~3 days to 6 months Trisomy 18 – Edward’s Syndrome (1 in 3,000 births US); survival rate after birth ~1-3 days Trisomy 21 – Down’s Syndrome (1 in 800 births & 6,000 born yearly US); Approximately 75% of concepti with trisomy 21 die in embryonic or fetal life. Approximately 85% of infants survive to age 1 year, and 50% can be expected to live longer than age 50 years. http://emedicine.medscape.com/article/943216-overview 17 Sex Chromosome Anomalies: Sex-chromosome monosomies: Turner’s Syndrome, XO (only 1 “X” chromosome) http://en.wikipedia.org/wiki/Turner_syndrome Sex-chromosome trisomies: Klinfelter’s Syndrome, XXY http://en.wikipedia.org/wiki/Klinefelter's_syndrome Supermale Syndrome, XYY http://en.wikipedia.org/wiki/XYY_syndrome Superfemale Syndrome, XXX http://en.wikipedia.org/wiki/Triple_X_syndrome 18 Turner’s Syndrome, XO Individual is a female 1 out of every 2,500 female live births worldwide. Individuals may have major heart defects, unusually short stature, loss of ovarian function, webbed neck, coarctation of the aorta, blocked lymphatic system, kidney malformation, diabetes, osteoporosis Individuals have normal intelligence, but may have difficulty with visual-spatial coordination 19 Turner’s Syndrome 20 Klinefelter’s Syndrome, XXY Individual is a male, having an extra X chromosome The principal effects are development of small testicles and reduced fertility Individuals are susceptible to breast tumors, germ cell tumors, diabetes, osteoporosis, pulmonary disease, rheumatoid arthritis It is the second most common extra chromosome condition, named after Dr. Harry Klinefelter, an endocrinologist at Mass General, Boston, MA The condition exists in roughly 1 out of every 500 to 1,000 males. It is not inheritable, caused by a single error (nondisjunction) during gamete formation 21 Klinefelter’s Syndrome Some examples of affected individuals 22 Supermale Syndrome, XYY XYY syndrome is characterized by an extra copy of the Y chromosome in each of a male's cells. Males with XYY syndrome are sometimes taller than average, increased risk of learning disabilities, delayed speech and language skills. Developmental delays and behavioral problems are possible, but vary widely among those affected Most have normal sexual development and are able to conceive children. About 1 in 1,000 males are born with an extra copy of the Y chromosome in each cell. Five to 10 boys with XYY syndrome are born in the United States each day Not inheritable, single error (nondisjunction) occurs in gamete formation 23