* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download You Light Up My Life
Human genetic variation wikipedia , lookup
Heritability of IQ wikipedia , lookup
Genetic engineering wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Genetically modified crops wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Saethre–Chotzen syndrome wikipedia , lookup
Genetic drift wikipedia , lookup
Transgenerational epigenetic inheritance wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Gene expression profiling wikipedia , lookup
Population genetics wikipedia , lookup
Genome evolution wikipedia , lookup
Hardy–Weinberg principle wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Hybrid (biology) wikipedia , lookup
History of genetic engineering wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Gene expression programming wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Genomic imprinting wikipedia , lookup
Neocentromere wikipedia , lookup
Y chromosome wikipedia , lookup
Genome (book) wikipedia , lookup
Designer baby wikipedia , lookup
X-inactivation wikipedia , lookup
Microevolution wikipedia , lookup
Observing Patterns in Inherited Traits Chapter 8 Cystic Fibrosis • Recessive genetic disorder; thick mucus in lungs, digestive tract shortens life span • Carriers of CF may not know they have mutant gene • Potential parents can be tested for gene Impacts, Issues Video One Bad Transporter and Cystic Fibrosis Gregor Mendel • Strong background in plant breeding and mathematics • Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring Genes • Units of information about specific traits • Passed from parents to offspring • Each has a specific location (locus) on a chromosome Alleles • Different molecular forms of a gene found on homologous chromosomes • Arise by mutation • Dominant allele masks a recessive allele that is paired with it Allele Combinations • Homozygous – having two identical alleles – Homozygous dominant, AA – Homozygous recessive, aa • Heterozygous – having two different alleles – Aa Chromosomes A pair of homologous chromosomes, each in the unduplicated state (most often, one from a male parent and its partner from a female parent) A gene locus (plural, loci), the location for a specific gene on a specific type of chromosome A pair of alleles (each being a certain molecular form of a gene) at correspinding loci on a pair of homologous chromosomes Three pairs of genes (at three loci on this pair of homologous chromosomes); same thing as three pairs of alleles Fig. 8-1, p.113 Genetic terms a Garden pea flower, cut in half. Sperm form in pollen grains, which originate in male floral parts (stamens). Eggs develop, fertilization takes place, and seeds mature in female floral parts (carpels). b Pollen from a plant that breeds true for purple flowers is brushed onto a floral bud of a plant that breeds true for white flowers. The white flower had its stamens snipped off. This is one way to guarantee a plant will not self-fertilize. c Later, seeds develop inside pods of the cross-fertilized plant. An embryo within each seed develops into a mature pea plant. d Each new plant’s flower color is indirect but observable evidence that hereditary material has been transmitted from the parent plants. Fig. 8-3, p.114 Gregor Mendel Crossing garden pea plants homozygous dominant parent homozygous recessive parent (chromosomes duplicated before meiosis) meiosis I meiosis II (gametes) (gametes) fertilization produces heterozygous offspring Fig. 8-4, p.114 Mendel’s Monohybrid Cross Results Monohybrid cross Dominant Form Recessive Form FLOWER COLOR 705 purple 224 white 3.15:1 FLOWER POSITION 651 along stem 207 at tip 3.14:1 STEM LENGTH 787 tall 227 dwarf Average F2 dominant-to-recessive ratio for all of the traits studied: 2.84:1 3:1 Fig. 8-5, p.115 Mendel’s Monohybrid Cross Results F2 ratios interaction Probability and the Punnett Square male gametes female gametes A a A a A A A aa a A a Aa aa a Aa a A a Aa A AA Aa aa a Aa aa Fig. 8-6a, p.115 POSSIBLE EVENT sperm A sperm A sperm a sperm a meets egg A meets egg a meets egg A meets egg a PROBABLE OUTCOME 1/4 AA offspring 1/4 Aa 1/4 Aa 1/4 aa p.115 Monohybrid Cross Experimental intercross between two F1 heterozygotes AA X aa Aa (F1 monohybrids) Aa X Aa ? A Monohybrid Cross True-breeding homozygous recessive parent plant F1 PHENOTYPES aa True-breeding homozygous dominant a parent plant Aa Aa Aa Aa a A Aa Aa A Aa Aa AA An F1 plant self-fertilizes and produces gametes: F2 PHENOTYPES Aa A AA Aa Aa aa a A AA Aa a Aa aa Monohybrid Cross Illustrated Testcross Mendel’s Theory of Segregation • Individual inherits a unit of information (allele) for a trait from each parent • During gamete formation, the alleles segregate from each other Dihybrid Cross AB X ab Experimental cross between individuals that are heterozygous for different versions of two traits Dihybrid Cross: F1 Results purple flowers, tall TRUEBREEDING PARENTS: AABB GAMETES: AB x white flowers, dwarf aabb AB ab ab AaBb F1 HYBRID OFFSPRING: all purple-flowered, tall 1 AABB purpleflowered, tall parent (homozygous dominant) AB X ab 2 aabb whiteflowered, dwarf parent (homozygous recessive) 3 F1 OUTCOME: All of the F1 plants are purple-flowered, tall (AaBb heterozygotes) Fig. 8-7, p.116 AaBb meiosis, gamete formation AaBb meiosis, gamete formation Fig. 8-7, p.116 Dihybrid Cross: F2 Results AaBb X AaBb 1/4 AB 1/4 Ab 1/4 aB 1/4 AB 1/4 Ab 1/4 aB 1/4 ab 1/4 ab 1/16 AABB 1/16 AABb 1/16 AaBB 1/16 AaBb 1/16 AABb 1/16 AAbb 1/16 AaBb 1/16 Aabb 1/16 AaBB 1/16 AaBb 1/16 aaBB 1/16 aaBb 1/16 AaBb 1/16 Aabb 1/16 aaBb 1/16 aabb 9/16 purple-flowered, tall 3/16 purple-flowered, dwarf 3/16 white-flowered, tall 1/16 white-flowered, dwarf Dihybrid Cross: F2 Results Dihybrid cross Independent Assortment • “Units” for one trait were assorted into gametes independently of the “units” for the other trait • Members of each pair of homologous chromosomes are randomly sorted into gametes during meiosis Independent Assortment Metaphase I: A A a a B B b b OR A A a a b b B B Metaphase II: Gametes: A A a a A A a a B B b b b b B B B A B A 1/4 AB b a b a 1/4 ab b A b A 1/4 Ab B a B a 1/4 aB Tremendous Variation Number of genotypes possible in offspring as a result of independent assortment and hybrid crossing is 3n (n is the number of gene loci at which the parents differ) Dominance Relations Complete dominance Codominance Incomplete dominance Codominance: ABO Blood Types • Gene that controls ABO type codes for enzyme that determines structure of a glycolipid on blood cells • Two alleles (IA and IB) are codominant when paired • Third allele (i) is recessive to others Fig. 8-9, p.118 ABO Blood Type: A Multiple Allele System Range of genotypes: Blood types: IA IA IB IB or or IA i IA I B IB i ii A AB B O ABO Blood Type Codominance: ABO blood types Incomplete Dominance X Incomplete homozygous homozygous parent parent Dominance All F1 are heterozygous F2 shows three phenotypes in 1:2:1 ratio X homozygous parent X homozygous parent All F1 offspring heterozygous for flower color: Cross two of the F1 plants and the F2 offspring will show three phenotypes in a 1:2:1 ratio: Fig. 8-10, p.118 Incomplete dominance Interactions among Gene Pairs • Common among genes for hair color in mammals BLACK LABRADOR YELLOW LABRADOR CHOCOLATE LABRADOR Pleiotropy • Alleles at a single locus may affect two or more traits – Marfan syndrome – Cystic fibrosis Fig. 8-12, p.119 Pleiotropy Pleiotropic effects of Marfan syndrome Continuous Variation • A continuous range of small differences in a given trait among individuals • The greater the number of genes and environmental factors that affect a trait, the more continuous the variation in that trait Number of individuals with some value of the trait Plotting Variation The line of a bell-shaped curve reveals continuous variation in the population Range of values for the trait Fig. 8-14a, p.120 Environmental Effects on Phenotype • Genotype and environment can interact to affect phenotype – Himalayan rabbit ice pack experiment – Transplantation of plant cuttings to different elevations – Human depression Coat Color Coat color in the Himalayan rabbit Environmental Effects on Phenotype Homologous Chromosomes • Homologous autosomes: – identical in length, size, shape, and gene sequence • Sex chromosomes: – nonidentical but still homologous • Homologous chromosomes interact, then segregate from one another during meiosis Karyotype Diagram 1 2 3 4 13 14 15 16 5 17 6 7 8 9 18 19 20 21 10 22 11 12 XX (or XY) Karyotype preparation Alleles • Different molecular forms of a gene • Arise through mutation • Diploid cell has a pair of alleles at each locus • Alleles on homologous chromosomes may be same or different Sex Determination female (XX) male (XY) eggs sperm X x Y X x X X X X XX XX Y XY XY Sex Determination Human sex determination The Y Chromosome • Small, with few genes • Master gene for male sex determination – SRY gene (sex-determining region of Y) • SRY present, testes form • SRY absent, ovaries form The X Chromosome • Carries more than 2,000 genes • Most genes deal with nonsexual traits • Genes on X chromosome can be expressed in both males and females Crossover Frequency Proportional to the distance between genes A B C D Crossing over will disrupt linkage between A and B more often than C and D Crossing Over Crossover review Pedigree Symbols male female marriage/mating offspring in order of birth, from left to right Individual showing trait being studied sex not specified I, II, III, IV... generation Fig. 8-22a, p.126 Genetic Abnormality • A rare, uncommon version of a trait • Polydactyly – Unusual number of toes or fingers – Does not cause health problems – View of trait as disfiguring is subjective Pedigree for Polydactyly Pedigree for Polydactyly Pedigree diagrams Genetic Disorder • Inherited conditions that cause mild to severe medical problems • Why don’t they disappear? – Mutation introduces new rare alleles – In heterozygotes, harmful allele is masked, so it can still be passed on to offspring Autosomal Dominant Inheritance Trait typically appears in every generation Achondroplasia • Autosomal dominant inheritance • Homozygous form usually leads to stillbirth • Heterozygotes display a type of dwarfism Autosomal dominant inheritance Autosomal Recessive Inheritance Patterns • If parents are both heterozygous, child will have a 25% chance of being affected Autosomal Recessive Inheritance Patterns Autosomal recessive inheritance X-Linked Recessive Inheritance • Males show disorder more than females • Son cannot inherit disorder from his father X-Linked Recessive Inheritance X-linked inheritance Examples of X-Linked Traits • Color blindness – Inability to distinguish among some or all colors • Hemophilia – Blood-clotting disorder – 1/7,000 males has allele for hemophilia A – Was common in European royal families Color Blindness Fig. 8-27, p.128 Hemophilia Structural Changes in Chromosomes • Duplication • Deletion • Inversion • Translocation Cri-du-chat Duplication normal chromosome one segment repeated three repeats Deletion • Loss of some segment of a chromosome • Most are lethal or cause serious disorder Inversion A linear stretch of DNA is reversed within the chromosome segments G, H, I become inverted Translocation one chromosome a nonhomologous chromosome nonreciprocal translocation In-text figure Page 206 Changes in Chromosome Number • Aneuploidy • Polyploidy • Most changes in chromosome number are due to nondisjuction Aneuploidy • Individuals have one extra or one less chromosome (2n + 1 or 2n - 1) • Major cause of human reproductive failure • Most human miscarriages are aneuploids Polyploidy • Individuals have three or more of each type of chromosome (3n, 4n) • Common in flowering plants • Lethal for humans – 99% die before birth – Newborns die soon after birth Nondisjunction n+1 n+1 n-1 chromosome alignments at metaphase I n-1 nondisjunction alignments at at anaphase I metaphase II anaphase II Down Syndrome • Trisomy of chromosome 21 • Mental impairment and a variety of additional defects • Can be detected before birth • Risk of Down syndrome increases dramatically when mothers are over age 35 Down Syndrome Turner Syndrome • Inheritance of only one X (XO) • 98% spontaneously aborted • Survivors are short, infertile females – No functional ovaries – Secondary sexual traits reduced – May be treated with hormones, surgery Klinefelter Syndrome • XXY condition • Results mainly from nondisjunction in mother (67%) • Phenotype is tall males – Sterile or nearly so – Feminized traits (sparse facial hair, somewhat enlarged breasts) – Treated with testosterone injections XYY Condition • Taller than average males • Most otherwise phenotypically normal • Some mentally impaired • Once mistakenly associated with criminal behavior Testing for Genetic Disorders • Carrier screening • Prenatal diagnosis – Amniocentesis – Chorionic villi sampling – Fetoscopy • Preimplantation diagnosis Amniocentesis Amniocentesis Fetoscopy • For prenatal diagnosis