biology summery

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1 - Human cells have 46 chromosomes, dogs have 78 chromosomes, a drosophila have 8 chromosomes Ploidy- (N) refers to number of sets of chromosomes in a cell i.e. humans have 23 pair of chromosomes. Therefore 2N=46 (Diploid) Haploid- (1N) is always half the diploid number (1N=23) Chromosomes- make up each pair and are homologues to one another (identical). Only exception is x and y which differ in size and content Eukaryotic chromosome- single DNA molecule packaged in a DNA-protein matrix called a chromatin Chromatin- Highly compact in mitosis and meiosis Sister chromatids- replicated chromosomes consist of two identical molecules of DNA called sister chromatids joined together at the centromere Centromere- chromosomal region where the spindle fibers attach during mitosis and meiosis. Position can vary (metacentric- middle, sub-metacentric- off center, acrocentric- nearly terminal, telocentric- terminal) Mitosis S phase (synthesis) - DNA replication occurs but this phase is considered pre-mitosis (46 chromosomes, 46 chromatids, 2C, 2N) M phase (mitosis)- most somatic cells have two mitotic division except nerve cells which only have one mitosis and stop at G1 G1 phase (growth)- S phase (DNA synthesis)- G2 phase- M phase- (46 chromosomes, 92 chromatids, 4C, 2N) prophase, metaphase, anaphase, telophase, cytokinesis only when the cell is splitting into daughter cells) (if parent cells are diploid, than daughter cells are diploid as well) Inter phase- periods between succeeding mitosis (G1, S, G2) Meiosis - Separates homologous pairs and reduces chromosome number by half - Occurs in germ line cells for animals, and produces gametes - Occurs In specialized cells found in anthers and pistils of flowers and produces spores - Involves two divisions Homolog- 2 non identical sister chromatids Meiosos 1- (pro, meta, Ana, telo, cyto) reduction division, Homologous pair exchange data and homologous chromosomes separate with one homolog moving to one end and other moving to other end. Cytokinesis produces two cells. Prophase 1- homologous chromosomes pair and exchange genetic info called crossing over. They lay side by side (synapsis) in a 4 chromatid complex and undergo crossing over (complex call bivalent/ tetrad) Crossing over- non-sister chromatid breaks and exchange genetic material Chiasmata- genetic exchange points between chromatids Metaphase 1- bivalent orient themselves and separate producing nuclei with half the number of chromosome Meiosis 2- non identical sister chromatids separate and form genetically unique haploid. Diploid is restored once fertilized. 2 Phenocopy effect- cosmetic surgery to give thin lipped people plump lips -In a structural gene the regulatory region determines when and how often transcription occurs -The protein encoding region specifies the amino acid sequence of the protein - RNA polymerase binds to promoter site (transcription factors bind to DNA Recessive Null/Amorphic alleles- a nonfunctional protein is produced or no protein is produced (no transcription/protein has no activity) - If mutation is in the protein-encoding region, there is a non-functional polypeptide leads to severe mutant phenotype - If mutation is in regulatory region there is no protein leads to severe mutant phenotype - Example of people with classic Albinism who are homozygous for a null allele of the tyrosinase gene (needed to synthesize melanin) Recessive Hypomorphic alleles- A poorly functioning protein is produced or reduced amounts of a normally functioning protein is produced (reduced transcription or a protein with reduced activity) - If mutation is in protein encoding region, there is a partially functional polypeptide leads to mild mutant phenotype - If mutation is in regulatory region, there is reduced amounts of a functional polypeptide leads to mild mutant phenotype - Himalayan and Siamese breeds are homozygous for a Hypomorphic allele of the tyrosine gene Autosomal recessive pedigrees- phenotypically normal parents have produced affected offspring (autosome means non sex chromosome) Dominant Hypermorphic alleles- negative phenotypic consequences due to the over production of a normal protein (mutations is in regulatory region-increased transcription) or negative phenotypic consequences due to the production of a protein with increased activity levels (mutation is in protein encoding region) Neomorphic alleles- negative phenotypic consequences due to the presence of an altered protein that has a new function or negative phenotypic consequences when altered protein interfered with wild type protein (dominant negative allele) (both occur in protein encoding region) - Ex Ehlers Danlos syndrome is a collagen disorder where individuals are heterozygous for a dominant neomorphic allele of one of the collagen genes Polygenic traits- trait is not controlled by single gene Complex/ multifactorial traits- environmental factors play an important role (for a single gene or polygenic) 3 Chromatin- eukaryotic chromosomes are made up of chromatin which is a complex of DNA and proteins Chromosomes- dynamic pieces of chromatins that can alternate between tight and loose compaction (highly compact during mitosis/meiosis-can only be visualized when compact) - They occupy specific regions of a nucleus called chromosome territories Karyotype- the number and appearance of chromosomes from a eukaryotic somatic cell - Chromosomes must be compacted and cell used for karyotyping must be mitotic - Chromosomes must be arranged in pairs, identical sister chromatids and be arrested in mitosis Karyotyping- In staining techniques (Giesma) the darks bands are often constitutive heterochromatic regions Constitutive Heterochromatin- Highly condensed, Gene poor, centromeres/ telomeres, no meiotic recombination Euchromatin- less condensed, gene rich, at chromosome arms, recombination at meiosis Sex chromosome- 300 genes in Y, while more than a 1000 in x Y chromosome- consists of heterochromatic regions, highly repetitive non coding DNA (the middle of a y chromosome is a non-recombining region, while end regions are called terminal regions) Heterogametic- X and y sperm Homogametic- X egg Female- no y chromosome therefore no TDF (Testes determining factor) is produced, lack of TDF allows cortex of embryonic gonads to develop ovaries, lack of testosterone produces embryo with female characteristics Male- Y chromosome produces TDF, TDF forces medulla of embryonic gonads to makes testes, and testes produce testosterone that makes embryo with male characteristics Birds- Females are ZW, Males are ZZ, and birds produce Z or W eggs (unfertilized turkey eggs can develop into offspring when chromosome sin eggs are doubled) Reptiles/Amphibians- XX/XY or ZZ/ZW or no sex chromosomes Turtles- sex of some turtles is determined by temperature , eggs incubation at temp above those indicated will result in female offspring in Celsius (Loggerhead- 30,, green-28, olive ridley-32, Japanese pond- 30) Ant/Bee/Wasps- use halplo-diplo system of sex determination (females workers and queens are diploid (can lay fertilized or unfertilized eggs) while male drones are haploid) Humans- XO (45 chromosome) female with turner syndrome - XXY (47 chromosomes)- male with klinefelter syndrome Drosophila- male determining genes are on the autosome while female determining genes are on X chromosome (xx- fertile female, xy- fertile male, x- sterile male, xxy- fertile female, note all these also include 6 autosomes) - Thomas Hunt Morgan’s experiments indicated that gene controlling eye color in fly’s maps to x chromosome - Red eyed males and females are common but white eyed males were rare Sex linked trait- controlled by X chromosome - Affected females always have affected fathers (sex linked recessive only) (helps determine if something is X linked or autosomal, in these type of questions always look at parents and daughters) Hemophilia- blood clotting disorders are controlled by X linked genes (clot formation requires platelets and protein fibrin) Classic Hemophilia (Hemophilia A, affects 85% of hemophiliacs) - Factor 8 is absent Christmas disease (B, 15%) - factor 9 is absent Factor 8- severe hemophilia have less than 1%, moderates have 1-5%, can be made using donor plasma or genetically modifying hamster cells (Queen Victoria, her granddaughter Alexandra and Alexandra’s only son had classic H) Colorblindness- red and green are encoded by two genes on the X chromosome while blue is encoded in an autosomal gene - Dichromatic people (missing red (1%), missing green (1.1%), missing blue (.001%) - Anomalously trichromatic people (have all pigments but may be abnormal (red sensitivity 10%, green sensitivity 49%) Duchene Muscular Dystrophy (DMD) - x linked trait that links cytoskeleton to portion in the membrane and leads to rapid progression of muscle degeneration - Leads to motor impairment and death Barr Bodies- darkly staining structure inside nucleus - Inactivated x chromosome not being transcribed (heterochromatin) - XY has no Barr while XX has one Barr, increase by one Barr for every extra X chromosome Dosage compensation (only in females) - inactivation of one X chromosome inn XX females equalizes X linked gene expression between males and females - Occurs during early embryonic development, 16 days post fertilization, random - Maternal X is active, paternal x is Barr therefore all the descendants of this cells will inactivate paternal x chromosome - Paternal X is active Maternal X is Barr therefore all the descendants of this cells will inactivate paternal x chromosome - Mammal females are mosaics: a mixture of previous two Anhidrotic Ectodermal Dysplasia (AED)-x linked disease with teeth/nail abnormalities and absence of sweat glands Turner syndrome (XO) - females are sterile and ovaries fail to develop, mosaic because two X chromosome are required 3 Independent assortment- two genes are on different chromosomes equals 4 classes of offs springs with equal frequencies - or the two genes are a x number of map units apart - pg. 48 is important Tightly Linked- genes are located near each other on the same chromosome and to classes of offspring with equal frequencies Cis configuration (alleles in coupling)-AB//ab Trans configuration (alleles in repulsion) - aB//Ab Linked with crossing over- crossing over occurs in pro 1 of meiosis 1 Parental- are the chromatid not involved in the crossing over (i.e. on the far left and right) Recombinant- produced by cross over - Parental will be two large classes and recombinants will two small classes The frequency of crossing-over between genes A and B is a measure of the distance between genes A and B Map units- (Number of recombinants/Total number of offspring) x 100- indicates the distance between gene A and Gene B 5 Incomplete/semi/partial dominance- the phenotype of the heterozygote can be distinguished from the phenotype of both homozygotes (i.e. AA is red and aa is white but Aa is pink) Hybrids do not breed true- If you cross a hybrid with a hybrid (Aa x Aa) you don’t get just hybrids Multiple alleles- some genes have many alleles and are governed by dominance hierarchy - For dogs S>Si>Sp (pie bald pigmentation on the head, saddle and rump)>Sw (so SS will I b solid) - Rabbits C>Cch>Ch>c - Cats C>Cb>Cs>Ca>c Blood types- Gene I encodes a tranferase enzyme - IA and IB encodes for either A or B antigen - IA encodes a transferase which adds acetlygalactosamine - IB is galactose - I is a non-functional transferase with no sugars added - IA IB both transferase and both proteins are made, this is called co dominant Lethal genotypes- not compatible with life - Mm cats are normal tail, Mm cats are bob tails , MM cats are dead - Huntington disease is a dominant lethal allele - Tay sach (often die before age 3) is a recessive lethal allele Variable expressivity- a range of phenotypes can be expressed by a genotype - Polydactyl is a rare autosomal dominant disorder with more than one thumb - Split hand-foot syndrome and pie baldism and neurofibromatosis is a rare autosomal dominant disorder that shows variable expressivity - Huntington disease is rare autosomal dominant disorder that shows variable expressivity in time onset of disease (neuro-degenerative disease starts around 45) Founder effect- certain alleles in a population can be traced to a few individuals (HD in Lake Maracaibo or Mauritius) Allelic heterogeneity- explains why variable expressivity is seen in certain diseases - I.e. cystic Fibrosis has alleles that show more severe of mild phenotypes - CF encodes a chloride channel protein that can lead to lung infections or digestion problems - Creates null alleles where the protein is absent and is severe or Hypomorphic alleles where there is reduced amounts of protein and is mild Incomplete penetrance- allele is not expressed even though it is present in an individual (polydactyl, split hand foot) - Penetrance value- # affected/ total # with allele - Neurofibromatosis shows penetrance value of 80%. 80% show trait while 20% do not Phenocopy effect- environmentally caused phenotype which mimics once cause by genes - Phocomelia is a genetic condition associated with absence/
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