* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download gene - Mrs. GM Biology 300
Human genetic variation wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Genome evolution wikipedia , lookup
Heritability of IQ wikipedia , lookup
Nutriepigenomics wikipedia , lookup
History of genetic engineering wikipedia , lookup
Public health genomics wikipedia , lookup
Transgenerational epigenetic inheritance wikipedia , lookup
Gene expression profiling wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Pharmacogenomics wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Behavioural genetics wikipedia , lookup
Population genetics wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Genetic drift wikipedia , lookup
Gene expression programming wikipedia , lookup
Neocentromere wikipedia , lookup
Y chromosome wikipedia , lookup
Medical genetics wikipedia , lookup
Genomic imprinting wikipedia , lookup
Genome (book) wikipedia , lookup
Designer baby wikipedia , lookup
Hardy–Weinberg principle wikipedia , lookup
X-inactivation wikipedia , lookup
Microevolution wikipedia , lookup
Unit 8: Genetics & Heredity Unit 9: Human Genetic Disorders Ch. 8: Heredity & Ch. 11: Human Genetics heredity Unit 8: Genetics & Heredity • What is genetics? – the study of heredity • passing of traits from parents to offspring Chromosomes in Cells • Remember… – body cells are diploid • 2 of each chromosome – 1 from mom & 1 from dad – gametes (sperm & eggs) are haploid • 1 of each chromosome – Why? » So zygote gets right # of chromosomes… Genes • Why is your combination of genes unique? – Chance. Which sperm will fertilize which egg? • get ½ your chromosomes from mom & ½ from dad • meiosis (formation of gametes) – crossing-over during prophase 1 – alignment of chromosomes during metaphase 1 Genes & Alleles • What is a “gene”? – section of chromosome that codes for a specific protein • & determines a specific trait (ex. hair color, eye color, ear shape, etc.) – genes are paired on homologous chromosomes (chromosomes that carry info for same type of trait) • different forms of genes for the same trait are called “alleles” – ex. brown eyes & blue eyes Dominant & Recessive Alleles • Each parent contributes 1 allele (form of gene) for trait & can be dominant or recessive – What is a dominant allele? • allele that prevents expression of (“masks”/“hides”) recessive trait – What is a recessive allele? • allele whose trait can be seen only when the organism is pure (homozygous) for that trait Dominant & Recessive Alleles • How are alleles represented? – with letters • usually the first letter of the dominant trait – If the same letter is used for dominant & recessive, how do we know which allele is which? » CAPITAL = DOMINANT » lowercase = recessive Allele Combinations • What does “homozygous” mean? – both alleles are the same • homozygous (pure) dominant (ex. AA) • homozygous (pure) recessive (ex. aa) • What does “heterozygous” mean? – both alleles are different • heterozygous (hybrid) (ex. Aa) Genotype vs. Phenotype • What is “genotype”? – organism’s actual genetic “code”/make-up (alleles) • What does the genotype do? – codes for protein that causes trait (phenotype) • How do we represent an organism’s genotype? – 2 letters (one for each allele) • one from mom & one from dad – ex. PP, Pp, pp Genotype vs. Phenotype • What is “phenotype”? – the outward (physical) expression of the genotype (trait we “see”) • What actually causes the “phenotype” (trait) we see? – the protein that is produced (due to the organism’s genotype “code”/alleles) • How do we represent an organism’s phenotype? – usually an adjective • ex. purple, white, tall, short, etc. Genotype is Expressed as a Phenotype • Ex. Let P = purple & p = white – homozygous (pure) dominant • genotype PP • phenotype = purple – homozygous (pure) recessive • genotype pp • phenotype = white – heterozygous (hybrid) • genotype Pp • phenotype = purple – dominant trait “masks/hides” recessive trait PP Pp pp Gregor Mendel • Father of Genetics – 1822-1884 • Wondered why certain traits disappear in one generation, yet reappear in the next & tried to determine how traits were passed from parent to offspring. Gregor Mendel • studied garden pea plants with 7 different traits with clearly different forms – bred hybrids – applied statistics • Deduced that consistent ratios of traits in offspring indicated that the plants transmitted distinct “units” Mendel’s Experiments • What happened when Mendel mated a pure purple parent (PP) & a pure white parent (pp)? – all F1 offspring: • purple phenotype • heterozygous (hybrid) genotype – Pp Mendel’s Experiments • What happened when Mendel let the heterozygous (hybrid) F1 offspring from his first experiment self-pollinate? – So… Pp x Pp (monohybrid cross) • F2 offspring weren’t all purple… 3 purple : 1 white – Always 3 :1 when both parents are hybrids Parent First filial Second Filial Crossed two F1 plants to get F2 Mendel’s Principle of Dominance • What did Mendel notice from his experiments? – white x white always produced white, but purple x purple produced ~3/4 purple & ~1/4 white • So, purple seemed to mask white sometimes. – …”dominant” trait prevented expression of “recessive” trait » PUPRLE = dominant » white = recessive Mendel’s Law of Segregation • during gamete formation, each gene for a trait separates so that each gamete receives only 1 of each gene – happens during meiosis I when homologous chromosomes line up & separate Test Cross • Mendel determined two genotypes resulting in purple flowers with test crosses – Bred dominant phenotype (unknown genotype) with recessive phenotype (“pure” homozygous since shows recessive trait) • If get all purple offspring parent = “pure” homozygous PP • If get ½ purple & ½ white offspring parent = “hybrid” heterozygous Pp Predicting Traits in Offspring • What are Punnett Squares? – a way to predict the results of crosses (mating) • letters outside represent possible alleles in gametes of each parent – top = one parent & side = other • letters inside boxes represent possible allele combinations (genotypes) in offspring (& phenotypes) Predicting Traits in Offspring • Punnett Squares can also be used to determine probability & ratios in possible offspring BB Bb Making a Punnett Square • Ex. Parents are Tt & tt genotypes… – So… Tt x tt is our cross (mating) Passing Traits to Offspring & Probability • What is probability? – chance an event will occur • What is the chance of getting heads? tails? –½ • If you flip two coins, of getting 2 heads? 2 tails? – ½ x ½ = 1/4 • What is the chance of a couple having a boy? a girl? – 1/2 • of having five girls? – ½ x ½ x ½ x ½ x ½ = 1/32 » or ( ½ )5 = 1/32 Passing Traits to Offspring & Ratios • What is a “genotypic ratio”? – probable ratio of genotypes (alleles) in offspring of a given cross • Ex. If cross Pp & Pp – 1PP : 2Pp : 1 pp Passing Traits to Offspring & Ratios • What is a “phenotypic ratio”? – probable ratio of phenotypes (traits) in offspring of a given cross – resulting from the genotypes of the offspring • Ex. If cross Pp & Pp • 3 purple : 1 white Passing Traits to Offspring & Ratios • What is an “expected ratio”? – ratio we expect to get based on probability (P. Square) • What is an “observed ratio”? – ratio we actually get • Why would these be different? – fertilization is random – some embryos die during early stages Mendel’s Principle of Independent Assortment • Genes for different traits segregate independently during gamete formation when they are located on different chromosomes… B A b B a b What if genes are on the same chromosome? • called “linked” • DO NOT sort independently Genes on same chromosome meiosis Genes on same chromosome Dihybrid Cross Animation Dihybrid Cross • involves study of inheritance patterns for organisms differing in 2 traits (each w/ 2 forms). – Mendel used dihybrid cross to determine if different traits of pea plants, such as flower color & seed shape, were inherited independently. Dihybrid Cross 2 traits with 2 forms Dihybrid Cross • To figure out combination of genes in gametes for two traits that are independently assorted use: – “foil” – (probability) tree diagram • Ex. Parent w/ AaBb genotype will make the following gametes: – AB – Ab – aB – ab B A b B a b When both parents are hybrid for both traits, Always get 9:3:3:1 ratio Dominant/Recessive is Not Always the Method of Inheritance • Traits are not always as clearly defined as the 7 pea plant traits Mendel studied. – examples of non-dominant/recessive inheritance • incomplete dominance • codominance • multiple alleles • sex determination • sex-linked traits • polygenic inheritance – Continuous variation Incomplete Dominance • No allele is dominant over another – results in 3 phenotypes – “dominant” 1, intermediate (mixed), “dominant” 2. • Genotypic & phenotypic ratios same – 1 CRCR : 2 CRCW : 1 CWCW – 1 red : 2 pink : 1 white – Ex. Pink four o’clock flowers Codominance • What is meant by codominance? – both alleles “expressed” equally • Ex. Roan cow = mixture of both red & white hairs Codominance –Ex. human blood types exhibit codominance (as well as multiple alleles) • A & B are codominant & “expressed” equally –IA = IB (codominant) –i (recessive) » So… (IA = IB ) > i •How many possible genotypes are there? •How many phenotypes? •Can you spot the blood type that is the result of codominance? Multiple Alleles • What is meant by multiple alleles? – more than 2 different forms of an allele exist • but individual has just 2 – 1 from mom & 1 from dad – Ex. human blood types • 3 alleles – IA (A) – IB (B) – i (o) •How many possible genotypes are there? •How many phenotypes? •Can you spot the blood type that is the result of codominance? antigen antigen antigens No antigens Multiple Alleles • Agouti rabbits – 4 alleles w/ dominance relationships • Agouti is dominant to chinchilla; both are dominant to Himalayan; all three are dominant to albino… C > cch > ch > c – agouti rabbit (wild type) » Phenotype: brown, Genotype: CC, Ccch, Cch, Cc – “Chinchilla” (mutant) » Phenotype: silvery gray, Genotype: cchcch, cchch, cchc – “Himalayan” (mutant) » Phenotype: white w/ black, Genotype: chch or chc – “Albino” (mutant) » Phenotype: white, Genotype: cc Sex Determination • How many chromosomes do humans have (in somatic cells)? – 46… 23 pairs • pairs 1 – 22 = autosomes (“body” chromosomes) • 23rd pair determines gender = sex chromosomes – XX = female – XY = male What is the probability of having a son? A daughter? Sex Determination • Which parent’s chromosomes determines if offspring will be a boy or girl???? Why? – Dad’s • if he gives X girl • If he gives Y boy – …mom always gives X • so it can’t be her What is the probability of having a son? A daughter? Sex-linked Inheritance • X & Y chromosomes not fully homologous. Why? – X is bigger & carries more genes Sex-linked Inheritance • How many alleles will a male have for traits carried only on the X chromosome? –ONE because only have one “X” chromosome (Y doesn’t have allele) • What is this called? –X-linked or sex-linked » Ex. eye color in fruit flies, hemophilia in humans, colorblindness in humans Sex-linked Inheritance • X-linked (recessive) traits & disorders are more common in males. Why??? – b/c female has XX, more likely she will have a copy of dominant allele… males = XY… can only get dominant allele on X (& only have 1 X) • female can be XGXG, XGXg, XgXg – normal, (normal) carrier, affected • male can only be XGY or XgY – normal or affected Sex-linked Inheritance • How do we make predictions made using Punnett squares for sex-linked traits? – Consider sex chromosome (X/Y) & allele for the trait it carries (“exponent”) TOGETHER as a unit… • ex. XG (= X w/ dominant allele), Xg (= X w/ recessive allele), Y (= Y w/ NO allele) Sex-linked Inheritance • What if a female is heterozygous (XGXg)? – she does not show the trait/have the disorder, but is a carrier • & can pass gene to offspring • Can a male be a carrier? – No, b/c only has one X chromosome w/ allele… so… either has it or doesn’t XG Y XG Xg XG XG XG Xg XG Y Xg Y Sex-linked Inheritance • Drosophila (fruit fly) eye color is sexlinked –Let XR = red eye allele, Xr = white eye allele, Y = no allele • What are sex, phenotype, & genotype of each offspring? Any carriers for white eye gene? –female w/ red eyes = XRXR –female w/ red eyes = XRXr » carrier for white eye gene –male w/ red eyes = XRY –male w/ white eyes = XrY XR Xr XR Y XR XR XR Y XR Xr Xr Y Polygenic Inheritance • What is polygenic inheritance? –When many genes affect a single trait • shows range of phenotypes from one extreme to other (continuous variation) –Ex. in humans: hair color, height, skin color Expression of Genes • Genes can interact with one another to control various other patterns of inheritance – Most characteristics that make up individual’s phenotype not inherited in Mendelian patterns • Ex. Modifier genes affect eye color – influence amount, intensity, & distribution of melanin (color pigment) in eye cells epistasis = phenomenon in which the expression of one gene depends on the presence of one or more 'modifier genes' Expression of Genes • Environment in which organism develops is another factor that affects expression – Probably due to how enzymes (proteins) operate at different temperature • Higher temps may “deactivate” enzyme & prevent a reaction form occurring (therefore, changing phenotype) Expression of Genes • Examples: – Himalayan hare: temperature & fur color… warm = white, cold = black Expression of Genes • Examples: – tobacco: green dominant & albino recessive • however color is also affected by environment – If no sunlight, green color cannot be expressed due to lack of chlorophyll production » put in light green will appear b/c chlorophyll being produced Unit 9: Human Genetic Disorders • What causes genetic disorders? – DNA mutation (usually recessive) or chromosome abnormalities (in # or structure) that cause the production of abnormal proteins Human Genetic Disorders • How can we group genetic disorders? 1. autosomal recessive disorders (*most genetic disorders) • allele is recessive & found on a chromosome from pairs 1 – 22 (autosomes or body chromosomes) – cystic fibrosis (CF), sickle-cell anemia, Tay-Sachs disease 2. autosomal dominant disorders • allele is dominant & found on a chromosome from pairs 1 – 22 (autosomes or body chromosomes) – Huntington’s Disease Human Genetic Disorders 3. sex-linked disorders • allele (which is usually recessive) is found on the 23rd pair of chromosomes (sex chromosomes)… Usually on the X chromosome – hemophilia, color blindness 4. chromosomal abnormality disorders • result from errors in chromosome # or structure – Down Syndrome (trisomy 21), Klinefelter’s Syndrome (XXY) Autosomal Recessive Disorders • What genotype(s) must a person have to be affected? – homozygous recessive (gg) • cystic fibrosis • sickle-cell anemia • Tay-Sachs Disease • Can someone be a carrier? Why/why not? – yes • if heterozygous (Gg), person carries gene, but isn’t affected – due to having the “normal” dominant gene Autosomal Dominant Disorders • What genotype(s) must a person have to be affected? – homozygous (GG) or heterozygous (Gg) b/c allele is dominant • Huntington’s Disease • Can someone be a carrier? Why/why not? – No • even if person is heterozygous (Gg), will have disorder – due to dominant “disease” gene blocking “normal” recessive gene Sex-linked Disorders • Recall… hemophilia is X-linked & recessive – What are the possible genotypes & phenotypes? Can someone be a carrier? • XHXH = normal female • XHXh = carrier female (but not affected) • XhXh = female w/ hemophilia • XHY = normal male • XhY = male w/ hemophilia Sex-linked Disorders –Why can’t a male be a carrier? • b/c only has one X chromosome w/ allele… so either has it or doesn’t –Ex. mom = carrier & dad = normal: • Make a Punnett square. –genotypic ratio? » 1 XHXH: 1 XHXh: 0 XhXh: 1 XHY: 1 XhY –phenotypic ratio? » 1 normal female: 1 carrier female (not affected) : 0 female w/ hemophilia: 1 normal male: 1 (affected) hemophiliac male Sex-linked Disorders • Recall… colorblindness is X-linked recessive – What are the possible genotypes & phenotypes? Can someone be a carrier? • XCXC = normal female • XCXc = carrier female (but not affected) • XcXc = colorblind female Ishihara test for • XCY = normal male redgreen c color• X Y = colorblind male blindness Sex-linked Disorders –In this Punnett square, what are genotypes & phenotypes of parents? • father: –genotype = XCY –phenotype = normal • mother: –genotype = XCXc –phenotype = carrier (but she is not affected) Chromosomal Abnormalities in Number • What causes an abnormal number of chromosomes? – non-disjunction • failure of paired chromosomes to separate during meiosis 1 or meiosis 2 Disorders Due to Abnormal Chromosome # • What is Down Syndrome (trisomy 21)? – when person has 3 copies of chromosome # 21 • What causes Down Syndrome (trisomy 21)? – non-disjunction • failure of paired chromosomes to separate during meiosis 1 or meiosis 2 Disorders Due to Abnormal Chromosome # • What is Klinefelter’s Syndrome? – a sex-chromosome disorder in which males have extra copy of X chromosome • XXY (or 47, XXY b/c 47 total chromosomes) • What causes Klinefelter’s Syndrome? – non-disjunction • failure of paired chromosomes to separate during meiosis 1 or meiosis 2 Chromosomal Abnormalities in Structure • What is causes structural abnormalities in chromosomes? − pieces are added, deleted, inverted, or translocated Detecting Abnormalities • Karyotyping –“picture of human chromosomes” • From blood sample –Can detect extra chromosomes or chromosomal abnormalities (additions, deletions, inversions, translocations) Detecting Abnormalities • Amniocentesis – sample of fluid surrounding fetus (karyotype then made) • Can detect Down Syndrome – 14th + week of pregnancy • Chorionic villus biopsy – sample of cells from chorion (part of structure by which fetus linked to mother) – 9th + week of pregnancy Pedigree Charts • A family tree (chart) of genetic history of family over several generations Square = male Circle = female Shaded = studied trait Marriage = horizontal line Offspring = vertical line Review & Animations • Vocab interactive – http://nortonbooks.com/college/biology/animations/ch10a02.htm • Crosses – http://www.sonefe.org/online-biyoloji-dersleri/grade-12/monohybrid-cross/ • Drag & drop genetics – http://www.zerobio.com/drag_gr11/mono.htm • Various – http://www.abpischools.org.uk/page/modules/genome/dna4.cfm?coSiteNavig ation_allTopic=1 • Genetic disorders – http://www.humanillnesses.com/original/Gas-Hep/Genetic-Diseases.html