Genetics Exam 1 Study Guide
Genetics Exam 1 Study Guide BSCI - 30156 - 002
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BSCI - 30156 - 002
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This 12 page Study Guide was uploaded by Jessica Brown on Monday February 8, 2016. The Study Guide belongs to BSCI - 30156 - 002 at Kent State University taught by Chi-hua Groff (P) in Fall 2015. Since its upload, it has received 159 views. For similar materials see ELEMENTS OF GENETICS in Biological Sciences at Kent State University.
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Date Created: 02/08/16
Genetics Module (Exam) One Study Guide Highlight: Vocab Word Highlight: Important information Highlight: Laws or Theory Terms to be familiar with… Human Genome: The complete DNA sequence of a person Nucleotide: Basic building block of DNA Phosphodiester Bond: A bond formed between a phosphate and a sugar of adjacent nucleotides DNA Replication: The Process by which DNA is copied Mutations: Mistakes that occur during the copying process Genetics: study of heredity and variation—how and why organisms have certain traits Phenotype: The physical (observable) traits. (Hair color, eye color, height etc) Karyotype: The 23 pairs of chromosomes. 22 autosomal and 1 pair of sex. Allele: A variation of a gene Coding DNA: Transcribed to make mRNA NonCoding DNA: regulates protein production. Is not transcribed. Critical for genome function. (many syndromes occur from mutations here) Human Genome 3.2 billion base pairs long 25,000 genes Each gene in our genome has two allelesone from each parent Single Polynucleotide Morphisms (SNPs)—occur once every 1,000 base pairs. o Causes people to have 3.2 billion base difference Important experiments 1. Griffiths a. Experiment with mice b. Heat killed S-bacteria transferred to living R-type bacteria i. This caused the R-bacteria to turn to S-bacteria with ability to kill the mouse. This is called transformation. ii. This experiment was important but didn’t tell us what the transforming substance c. Avery et al experiment: Identified the transforming substance as DNA 2. Hershey and Chase a. Further identified DNA as the genetic material 3. Watson and Crick a. Discovered the structure of DNA i. DNA is a base, sugar and a phosphate group ii. One strand of DNA is basically a chain of nucleotides joined together by strong phosphodiester bonds (backbone) Deoxyribonucleic Acid (DNA) Double stranded helix o Formed by complementary bases being paired and bonded by H bonds A pairs T 2 hydrogen bonds G pairs C 3 hydrogen bonds This makes G-C bonds stronger than A-T bonds DNA strands run antiparallel DNA replication o The entire genome is copied in the nucleus prior to cell division o Mutations occur but are not always detrimental. They are most neutral (have no effect) o Replication is semi-conservative Prior to replication, DNA unwinds, hydrogen bonds between pairs break resulting in two strands (parent and original) These are now the templates for new DNA Mitosis and Meiosis Humans are diploid o Somatic cells: 2n=46 o Germ Cells: n=23 o Zygote: 2n=46 One set from each parent Prior to cell division, DNA replicates in the S (synthesis) phase! Mitosis This is the cell division of somatic cells Genetic purpose: produce two daughter cells o Daughter cells are identical to each other and the parents Phases G1, G2, (gap phases) and S are all apart of interphase G0(just prior to S phase)—cells that are here for long period of time are “arrested” and will not continue cell division S phase o Chromosomes are replicated—forming sister chromatids They link together and become one chromosome At this point the cell has double the sister chromatids M Phase o Cell distributes the replicated chromosomes Each new daughter cell has an exact complement of chromosomes that were found in the original cell 1. Prophase a. Nuclear membrane dissociates i. Chromosomes condense b. Mitotic spindle begins to form 2. Prometaphase a. Interaction of spindle fibers with chromosomes 3. Metaphase a. Chromosomes align themselves along the central plane i. This is known as the metaphase plate b. There is NO pairing of homologous chromosomes—this is the key difference from meiosis 4. Anaphase a. Connection between sister chromatids breaks b. Chromosomes start to sort c. Chromatids linked to only one of the poles i. Each chromatid is now considered to be an independent chromosome d. Chromosomes begin to migrate to their respective poles 5. Telophase a. Once chromosomes reach their side they begin to decondense b. Nuclear membrane reforms around chromosomes 6. Cytokinesis a. Splits the cell into two identical daughter cells i. Note: Small variations (mutations) are possible due to errors during DNA replication Meiosis Cell division of the germ cells Genetic purpose: to produce 2 daughter cells with ½ the chromosomes as the parent cell o Daughter cells are not identical to each other or the parents o Parent cell=2n (diploid) Daughter cell=n (haploid) Mendel’s Laws of Inheritance are based on meiosis Phases 1. Phophase 1 a. Pairing of homologous chromosomes b. Formation of synaptonemal complexes i. A and B are the key things that makes meiosis different then mitosis c. Stage one of prophase: Leptotene i. Chromosomes start to condense forming threadlike structures d. Stage two of prophase: Zygotene i. Homologous chromosomes recognize each other through synapsis ii. Chromosomes align along their entire length with each other 1. Know they’re called bivalents or tetrads a. There are 4 sister chromatids in one tetrad iii. Tetrads form the synaptonemal complex between chromosomes. 1. Synaptonemal complexes consist of lateral and central elements e. Stage three of prophase: Pachtyene i. Right before the third stage is when crossing over occurs 1. Site of crossing over is called the Chiasma f. Stage four of prophase: Diplotene i. Synaptonemal complex dissociates ii. At this point the chromatids are usually able to be seen g. Final State of phrophase: Diakinesis i. Synaptonemal complex has entirely disappeared Here are a few mnemonics to help you remember the order of the stages of prophase. Use which ever one you will remember or make your own Let’s Zip Past Dunkin Doughnuts Loud Zaps Pester Doctor Dum Lions Zig Past Dark Doctors 1. Prometaphase 1 a. Resemble those of mitosis—the spindle apparatus is complete i. The chromatids are attached via kinetochore microtubules 2. Metaphase 1 a. Chromosomes align in the middle of the cell i. Tetrads are aligned in a double row ii. Kinetochore microtubules link each chromosome to separate poles (one set of mt’s to one chromosome) 3. Anaphase 1 a. Homologous chromosomes separate i. Migrate towards the other pole ii. Sister chromatids remain connected throughout meiosis 1 4. Telophase 1 a. Chromosomes reach their destination at opposite poles i. They begin to decondense b. Nuclear membrane begins to reform around the chromosomes 5. Cytokenesis a. The cell divides into two separate cells (unidentical to each other) Sequence of events for meiosis 2 is identical to that of meiosis 1 Only difference is that instead of one cell dividing into two you have two cells dividing into 4 total cells The 4 daughter cells that result from meiosis are not identical to either of the other daughters or the parents The second half of meiosis is called reduction division Human disorders are believed to be caused by nondisjunction in meiosis—leading to abnormal karyotypes Aneuploidy: variations in chromosome number that involve one or more chromosomes o Arises from errors in meiosis o Results from nondisjunction Remember the mnemonic device to (generally) remember the steps of mitosis and meiosis Put My Answer There Mendel’s Laws Law of segregation: Two copies of a gene segregate (or separate) from each other during transmission from parent to offspring Mendelian inheritance can only work on single trait on a single loci! o This means most traits will not follow Mendelian inheritance Mendel assesses single factor crosses o Look in the book and see his experiments with the pea plants His experiment disproves previous thoughts of “blending inheritance.” Blending Inheritance: Tall x Short = Medium It showed that one trait was dominant over the other trait o Test cross: this is a way used to figure out if a dominant phenotype is homozygous or heterozygous Cross a parent with a true breeding homozygous recessive If an individual is homozygous they have two of the same alleles (DD) (dd) o If they are heterozygous they contain two different alleles (Dd) Punnet Squares: Used to predict the outcome of offspring o Predict types of offspring and the proportion of the trait in the offspring Law of Independent Assortment: Two different genes will randomly assort their alleles during the formation of haploid cells Mendel assesses two different characters o Dihybrid cross 9:3:3:1 phenotypic ratio o Two possibilities of how traits are inherited They can be linked to another and inherited as one unit They can be unlinked and assort themselves independently during inheritance His experiment was similar to the one used in his first law Shows that a single individual can produce a very diverse set of genetically different gametes Genetic Recombination: When an offspring receives different combination of alleles than are seen in the parental generation (Crossing over) Chromosome Theory of Inheritance: the relationship between the chromosomal transmission and the patterns of inheritance as described by Mendel Principals of Chromosome theory of inheritance o Chromosomes contain genetic material o Chromosomes are replicated and passed on o Nuclei of most eukaryotic cells are diploid o During formation of haploid cells the chromosomes will segregate independently Mendel’s law of segregation o One set of chromosomes is inherited from the father and the other set is inherited from the mother Mutations Mutation: a heritable change in the genetic material We are mostly concerned with mutations that travel through the germline o Can occur in both germ or somatic cells Mutations provide us with allelic variation Can cause evolutionary change if the change offers a selective advantage o Can also be detrimental if it causes an allele to function worse than it did before the mutation Mutations occur at the chromosomal level and the molecular level o Molecular Level: not detectable via karyotypes but usually will affect a gene DNA changes that Change one nucleotide to a different one Delete a nucleotide Insert nuceleotides DNA sequence mutations can alter the coding sequence within a gene Silent, missense, nonsense, frameshift DNA sequence mutations have the ability to occur outside of the coding sequence This causes it to influence gene transcription and expression o Chromosomal Mutations: Generally can be seen in the karyotype of an individual and have an effect on more than one Inversions Translocations Duplications Deletions Changes in chromosome structure can play a part in affecting gene transcription Changes in chromosome number is due to nondisjunction Mutations are random! (stochastic) and get lost due to genetic drift Once a mutation becomes fixed and affects the phenotype, suppressor mutations can occur o Suppressor mutations have the ability to reverse or greatly alleviate the mutations phenotypic consequence. Think of autism—it’s a wide spectrum disease and varies in its effect on certain people. This is due to multiple loci interacting, environmental factors and how many suppressor mutations that an individual has Studying Inheritance Patterns in Humans 3 types of inheritance 1. Autosomal dominant (HH) (Hh) 2. Autosomal Recessive (hh) 3. X-Linked (X*X) (X*X*) Pedigree: a family tree used to examine inheritance patterns in humans o Often times we use this to discover things about human disease o Recall the symbols used for pedigrees! o Example is cystic fibrosis Know that cystic fibrosis is an autosomal recessive disease! Probability and statistics Mendel demonstrated that we can use the laws of inheritance to predict the outcomes of genetic crosses o Use probability calculations Probability: The likelihood of an event occurring (or chance a future event will take place) o Calculating probability Probability = Number of times an event occurs/ total number of events Sample sizes determine the accuracy of a probability calculation Random Sampling Error: The deviation between observed outcome and the expected outcome o The Sum Rule: the probability that one of two or more mutually exclusive events will occur is equal to the sum of the individual probabilities of the event Based on an “or” event What is the probability that event A or B will occur o P= p(A) + p(B) Calculate the individual phenotype then add together o The Product Rule: The probability that two or more independent events will occur is equal to the product of their individual probabilities Based on an “and” event What is the probability that even A and B will occur? o P = p(A) x p(B) Calculate the individuals probability of the phenotype, then multiply them together Be sure to practice punnet squares and probability!! Sex Chromosomes/Determination Sex Determination systems 1. XY system (mammals) a. Male Heterogametic (or hemizygotic) XY b. Female is homogametic XX 2. X-O systems (insects) a. Male has one sex chromosome b. Females have two sex chromosomes 3. Z-W system (birds and some fish) a. Male is homogametic sex b. Female is heterogametic Dosage compensation and X inactivation Dosage compensation: regulates the expression of genes on the sex chromosomes so that the gene product is the same in both sexes Recall: When you have two of something it usually results in over production. Therefore, in human females having XX causes over production. In order to balance this, we have dosage compensation Dosage compensation is necessary for certain species to make sure that there is genetic equality between the sexes o In mammals: X inactivation o In Drosophila: X-linked gene expressions are doubled o C elegans: XX are hermaphrodites and X is a male XX individual is compensating by reducing the gene expression to 50% X-Inactivation The process that mammals use to compensate for the extra X o Purposed by Lyon and Russel (1961) Somatic cells only express one of the X chromosomes at a time Is random on which one is expressed Barr Body: a highly condensed region within a somatic cell that contains the inactivated X Once inactivated this X will remain inactivated in all future progeny cells produced by mitosis XIST gene o Required to pack the inactive X into a barr body o Is active on the inactive X It produces RNA that coats the X chromosome—this is what causes it to go inactive X-Inactivation Phases 1. Initiation: One X chromosome is chosen to remain active. The one that isn’t chosen goes inactive 2. Spreading: The XIST RNA coats the inactivated X which leads to it becoming compacted into the barr body 3. Maintenance: Barr Body remains compacted through all of the future cell divisions Properties of X and Y chromosomes A sex linked gene is found on one of the sex chromosomes o X-Linked: genes located on the X chromosome Remember males are more likely to get x linked traits because they only have one X o Y-Linked: genes located on the Y chromosome Y chromosome contains an SRY gene o This gene encodes to turn on the pathways for the embryo to become a male Recognizing X linked recessive inheritance patterns in a pedigree 1. More males then females affected 2. Affected sons born to unaffected mother a. Meaning that the trait has the ability to skip generations 3. Approximately ½ of a carriers (heterozygous female) sons are affected 4. Never passed from father to son 5. All daughters of an affected father become carriers Recognizing X linked dominant inheritance patterns in a pedigree 1. Both genders are affected—often times more females then males 2. The trait will not skip generations a. Affected sons must have an affected mother 3. Affected fathers will pass on the trait to all of their daughters a. This is because they only have one X to give and since this is a dominant trait the only X an affected father can give is dominant. i. Recall: you only need one dominant allele to be affected by a dominant disease 4. Affected mother (if heterozygous) will pass on the trait to ½ sons and ½ daughters a. This is because she has one normal x and one dominant (affected) X. This means she can give one of these to her offspring meaning there is a 50/50 chance of her giving one of the X’s Gametogenesis In animals Spermatogenesis: Formation of sperm in the testes of male animals In the testes the spermatogonial cell divides by mitosis o This creates two identical cells One is a spermatocyte which enters meiosis Four haploid cells produced from meiosis end up becoming sperm cells o Each sperm cell contains… Haploid nucleus Acrosome (contains digestive enzymes) Long Falgellum (tail) Other remains a spermatogonial cell Oogenesis: The formation of egg cells in the ovaries of a female. Begins with an oogonia going into meiosis o Gets arrested at prophase 1 Once female reaches reproductive age, primary oocytes are periodically activated o Most females will have 300-400 total eggs Oogenesis only produces one egg cell o During cytoplasm division two polar bodies are created The larger=the secondary oocyte This is the cell that is released during ovulation o If fertilized, it completes meiosis 2 Practice Questions Mendelian Inheritance can not be used for traits such as eye color. Why is this? Genotype has a huge effect on phenotype. Why? In what phase of meiosis do sister chromatids pair? a.) Telophase 1 b.) Anaphase 2 c.) Cytokinesis d.) Prophase 1 What is the key difference between mitosis and meiosis? Monosomy is lethal if it is on any other chromosome aside from the sex chromosome. Why is this? What is aneuploidy and what is it a result of? Autosomal dominant diseases only require one allele to be dominant for the phenotype to be affected. Why? What is Mendel’s Law of independent assortment? If an individual has a dominant phenotype, what is the best way to determine the person’s genotype? What are the three patterns of inheritance? When looking at a pedigree, how can you tell if a disease is autosomal recessive? Why can’t individuals with an autosomal dominant phenotype not be a carrier? What is the purpose of the XIST region on X chromosomes? Why do sex linked traits not affect males and females equally?
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