* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 10
Non-coding RNA wikipedia , lookup
Long non-coding RNA wikipedia , lookup
Saethre–Chotzen syndrome wikipedia , lookup
Genetic engineering wikipedia , lookup
Essential gene wikipedia , lookup
Gene nomenclature wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Gene desert wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Frameshift mutation wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Epigenetics of neurodegenerative diseases wikipedia , lookup
Oncogenomics wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Therapeutic gene modulation wikipedia , lookup
History of genetic engineering wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Ridge (biology) wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Neocentromere wikipedia , lookup
Y chromosome wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Minimal genome wikipedia , lookup
Gene expression programming wikipedia , lookup
Genome evolution wikipedia , lookup
Genomic imprinting wikipedia , lookup
Gene expression profiling wikipedia , lookup
Point mutation wikipedia , lookup
Designer baby wikipedia , lookup
Genome (book) wikipedia , lookup
X-inactivation wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Chapter 10 10.1 The Chromosome Theory of Heredity Chromosomes are located in the nucleus Factors (genes) are found on chromosomes Sutton discovered that genes are on chromosomes in 1902 Chromosome Theory of Heredity States that genes are located on chromosomes and each gene occupies a specific place on a chromosome Only one allele is on a chromosome Independent Assortment Gene Linkage Genes on a chromosome are linked together Inherited together – THEREFORE they do not undergo independent assortment Linked Genes- genes on the same chromosome – inherited as a package A Height Gene B Flower color gene C Flower position gene Thomas Hunt Morgan Studied fruit flies – Drosophilia melanogaster Fruit Flies are excellent for genetic studies because: Reproduce quickly Easy to raise Many mutations Have 8 chromosomes (n=4) Fruit Fly Mutations Thomas Hunt Morgan began to carry out experiments with Morgan looked at TWO traits Gray bodies – G Normal Wings - W Black bodies – g Small wings – w The flies mated…. The female laid eggs P1 F1 GGWW x GgWw 100% ggww Morgan then mated the F1 back to the recessive parent GgWw x ggww Expected ratio – 1:1:1:1 25% GgWw 25% ggWw 25% Ggww 25% ggww Morgan’s Actual Results 41.5% 41.5% 8.5 % 8.5% gray normal black small black normal gray small Conclusion Gene for body size and wing color were somehow connected or linked Can’t undergo independent assortment Linkage Groups Package of genes that are always inherited together Chromosome One linkage group for each homologous pair Fruit flies – 4 linkage groups Humans – 23 linkage groups Corn – 10 linkage groups So linkage groups explain the high percentages (41.5%) but What about the 8.5%?????? 17% had new combinations The combinations that were expected would be: Gray normal – GW or Black small - gw P1 G G g g W W w w Mom Dad F1 G g W w G g g g W w w w F1 F1 F1 Heterozygous X Recessive Fruit Fly The Offspring of the Cross g G g g w w and W w F1 F1 41.5 % 41.5 % Genes of the Heterozygous Parent G G g g W W w w The homologous pair copied The homolgous pairs pair up in Prophase and form a tetrad G G g g W W w w When they are lined up they can become twisted and switch genes Crossing Over So you could then have ….. G G g g W w W w switch The other offspring of the cross g G g g W w and w w F1 F1 8.5 % 8.5 % The 17% that had new combinations are known as Recombinants – individuals with new combinations of genes Crossing Over – gives rise to new combinations – Prophase I Gene Mapping Sturtevant – associate of Morgan Crossing over occurs at random The distance between two genes determines how often they cross over Genes that are close do not crossover often Genes that are far apart – cross over often So…… If you know the frequency with which crossing over occurs then you can use that to map the position of the genes on the chromosome Frequency of crossover exchange... is GREATER the FARTHER apart 2 genes are is proportional to relative distance between 2 linked genes Relative distance is established as... 1% crossover frequency = 1 map unit of map distance 1% CrossOver Freq = 1 centiMorgan Sex Linkage Stevens – made observations of meal worm chromosomes Sex Chromosomes One pair Female – XX Male – XY Autosomes All the chromosomes except the sex chromosomes Sex Determination Genes on Sex Chromosomes Sex chromosomes determine a person’s sex Sex chromosomes also contain genes Sex Linked A gene located on a sex chromosome Usually X Example – Fruit Fly Eye Color So the gene for eye color is on the X chromosome and not the Y Fruit Fly Sex Chromosomes X X X Y Males Females XRXR XRY Red Eyed XRXr XrXr White Eyed XrY Mutations A change in the DNA of an organism Can involve an entire chromosome or a single DNA nucleotide and they may take place in any cell Germ Cell Mutation Occur in an organism’s germ cells (gametes)- can only affect offpsring Somatic Mutations Take place in an organisms body cells and can affect the organism Lethal Mutation Cause death, often before birth Good Mutations Some mutations can be beneficial – these organisms have a better chance to reproduce and therefore have an evolutionary advantage Provide the variation on which natural selection acts Chromosome Mutations Are either changes in the structure of a chromosome or the loss of an entire chromosome or an addition Four Types (duplication, deletion, inversion and translocation) Duplication – segment of a chromosome is repeated Deletion – the loss of a chromosome or part due to chromosomal breakage – that information is lost Inversion – a chromosomal segment breaks off and then reattached in reverse orientation to the same chromosome Translocation – a chromosome breaks off and reattaches to another nonhomologous chromosome Nondisjunction Some chromosome mutations alter the number of chromosomes found in a cell Nondisjunction – the failure of a chromosome to separate from its homologue during meiosis Gene Mutations May involve large segments of DNA or a single nucleotide within a codon Involve individual genes Point Mutations – 3 types The substitution, addition or removal of a single nucleotide 1. Substitution – a point mutation where one nucleotide in a codon is replaced with a different nucleotide, resulting in a new codon Ex. Sickle Cell Anemia – sub. Of A for T in a single codon 2 & 3. Insertion and Deletions – one or more nucleotides is lost or added – have more serious effects Frameshift Mutation When a nucleotide is lost or added so that the remaining codons are grouped incorrectly Insertions and deletions are frameshift mutations THE FAT CAT ATE THE RAT Polyploidy Condition in which an organism has an extra set of chromosomes 3N, 4N Usually fatal in animals Plants – usually more robust Caused by - Nondisjunction 10-3 Regulation of Gene Expression As biologists have intensified their studies of gene activity, it has become clear that interactions between different genes and between genes and their environment are critically important Gene Interactions Gene – piece of DNA – DNA codes for proteins In many cases the dominant allele codes for a protein that works and the recessive allele codes for a protein that does not work Incomplete Dominance When offspring have a phenotype that is in-between the two parents Occurs when two or more alleles influence the phenotype Example – flowers – four o’ clocks, snapdragons Alleles – R/R’, R/r, R/W, FR F r Red Flower White Flower Pink Flower Red mixed with white makes pink Incomplete Dominance Example #2 Incomplete dominance is a half way between point. Halfway to dark blue is light blue. Incomplete Dominance is not a blending. RR rr Rr Phenotypic Ratio: 1:2:1 Genotypic Ratio: 1:2:1 Codominace Occurs when both alleles for a gene are expressed in a heterozygous offspring Neither allele is dominant or recessive Example – horse coat color Horse Coat Color Red – HR HR White – HWHW Roan – HR HW Roan – red and white hairs Blue roan - The coat has white hairs and blue hairs Polygenic Inheritance Traits controlled by two or more genes Examples – height, skin color, coat patterns Phenotypes are seen in a range Polygenic Inheritance AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb Gene Expression in Prokaryotes Genes serve as a pattern for the production of mRNA mRNA serves as the instructions to make a protein All the genes of an organism can’t be active all the time When a cell needs a product it must be able to make it fast When the product of a gene is being made we say the gene is being expressed Genes are: Rarely expressed Constantly expressed Turn on and off The Operon Genes that work together are clustered together Some genes in the cluster do not code for proteins instead they are involved in regulation and expression Operon Genes that work together Operator Promotor There is slight overlap between the operator and the promotor Inducer Molecule that causes the production of a protein To Make a Protein RNA polymerase must attach to the promoter (“Start here”) Moves along to the genes mRNA The Repressor Special protein Attaches itself to the RNA between the promotor and the genes Does not let RNA polymerase make a protein Turns off genes Each repressor has a special shape that allows it to attach to a specific piece of RNA Gene Activation When an inducer enters a cell it binds to the repressor The repressor changes shape and can no longer bond RNA polymerase can then attach Proteins eats up the inducer repressor attaches again Ex. Lactose – sugar – food for bacteria Gene Expression in Eukaryotes More complex than Eukaryotes More DNA in a nucleus 1976 – Sharp and Berget Discovered mRNA produced during transcription may be altered before it is used to make a protein DNA mRNA not an exact copy as was thought – not complementary Exons Sequences that code for a protein Expressed sequences Introns Segments that do not code for a protein Intervening sequences IN the way