PCB3063 Exam 1 Study Guide PDF

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PCB3063 Exam 1 Study Guide...

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PCB3063 Exam 1 Study Guide

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1. Be able to differentiate the following inheritance patterns from pedigrees: autosomal dominant  Appear in every generation  Males & females equally affected  All affected individuals have an affected parent  Most affected individuals are heterozygotes autosomal recessive  Skips generations  Males & females equally affected  All affected individuals are homozygous recessive  Unaffected parents of affected offspring are obligate heterozygotes  Occurs more often in consanguineous matings X-linked dominant  disorders caused by mutations in genes on the X chromosome,  In females (who have two X chromosomes), a mutation in one of the two copies of the gene in each cell is sufficient to cause the disorder.  In males (who have only one X chromosome), a mutation in the only copy of the gene in each cell causes the disorder.  males experience more severe symptoms of the disorder than females  No male to male transmission X-linked recessive  disorders caused by mutations in genes on the X chromosome.  In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition.  In females (who have two X chromosomes), a mutation would have to occur in both copies of the gene to cause the disorder.  affect males more frequently  no male-to-male transmission Mitochondrial  no transmission from M  maternal inheritance  potential for the disease to affect both sons and daughters of affected F

2. Be prepared to calculate probabilities based on pedigrees. 1

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3. Know the expected ratios of phenotypes & genotypes for the following Mendelian and NonMendelian crosses: Mendelian monohybrid:  The traits of the parent plants do not blend  Genotypic ratio 1:2:1  Phenotypic ratio 3:1 Mendelian dihybrid:  Alleles for different traits separate independently  Phenotypic ratio 9:3:3:1 Incomplete dominance:  F1 hybrids that differ from both parents express an intermediate phenotype – “blending”.  Neither allele is dominant or recessive to the other.  Phenotypic ratios are same as genotypic ratios  1:2:1 Codominance:  F1 hybrids express the phenotypes of both parents equally.  Neither allele is dominant or recessive to the other.  Phenotypic ratios are same as genotypic ratios.  1:2:1 Dominant epistasis:  Dominant alleles for one gene are epistatic to a second  12:3:1 phenotypic ratio or 13:3 Recessive epistasis:  Recessive alleles for one gene are epistatic to a second 2

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 9:4:3 phenotypic ratio Dominant X-linked Recessive X-linked Dominant lethal   

only need one copy of the allele to cause lethality late onset and new mutations most undetected

Recessive lethal    

needs 2 copies of the allele to cause lethality late onset and new mutations gene product essential for survival 2:1 phenotypic

Complementary gene action:  

Two genes work together to produce a phenotype. Dominant alleles of two genes act together to produce a trait

 9:7 ratio is a phenotypic signature of complementary gene interaction Duplicate gene action: 

Two genes involved but a dominant allele for either gene is sufficient to produce the phenotype

 15:1 ratio Multiple alleles 

Three or more forms of a gene that code for a single trait

Mitochondrial  no transmission from M  maternal inheritance  potential for the disease to affect both sons and daughters of affected F 4. Define the following key terms:  Homozygote: an individual with 2 identical alleles for a gene  Heterozygote: an individual with 2 different alleles for a gene  Hemizygote: haploid for genes on X  Heteroplasmy: Presence of two or more distinct variants of DNA within the cytoplasm of a single cell.  Sister chromatid: one of a pair of identical chromosomes created before a cell divides  Homologous chromosome: Chromosomes that have the same sequence of genes and the same structure  Variable expressivity: individuals who carry alleles for a trait show a phenotype, but to a varying degree of severity (Waardenburg Syndrome)  Penetrance: percentage of a population with a particular genotype that show the expected phenotype, can be complete (100%) or incomplete (e.g., retinoblastoma penetrance is 75%).  Anticipation: a phenomenon where the symptoms of a genetic disorder become apparent at an earlier age with each generation (Huntington's)  Paternal transmission bias: like anticipation but for paternal 3

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PCB3063 Exam 1 Study Guide

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Dynamic mutation: a type of mutation in which a repeated sequence, such as three nucleotides, can readily increase in number from one generation to the next. Pleiotropy: A single gene having multiple effects on an individuals phenotype Genotype: the specific alleles of genes in DNA Phenotype: observable/measurable physical traits Haplotype: A group of alleles of different genes on a single chromosome that are closely enough linked to be inherited usually as a unit Karyotype: organized picture of chromosomes in the cell Diploid: 2 copies of each chromosome Haploid: 1 copy of each chromosome Kinetochore: protein complexes that assemble on the centromeric regions of the chromosomes Centriole/Centrosome: produce spindle fibers during cell division Chiasmata: crossover points Nondisjunction: Error in meiosis in which homologous chromosomes fail to separate. Consanguinity: blood relationship

5. List and describe the phases of mitosis.  Interphase o Chromosomes uncoiled- chromatin DNA replication- S phase  Prophase (a) o Chomosomes condense, centrioles divide and migrate, nucleolus disappears  Prometaphase o Centrioles at poles, nuclear membrane breaks down, spindles attach to kinetochores  Metaphase (b) o Chromo aligned midline, spindle microtubules visible  Anaphase (c) o Centromeres split, daughter chromo move to opposite poles  Telophase (d) o Nuclear membranes reform, chromo decondense, cell furrow/plate 6. List and describe the phases of meiosis.

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7. Describe the processes that take place in each substage of Prophase I of meiosis. 5

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Leptonema o Chromatin condenses, chromosomes visible, homology search begins, homologous chromosomes start to align Zygonema o Condensation cont., initial alignment (300 nm), lateral elements visible, synaptonemal complex forms – bivalents Pachynema o Condensation cont., synapsis & homologous recombination (100 nm), 4 chromatids/bivalent = tetrad Diplonema o Chiasmata visible between non-sister chromatids, pairs of sister chromatids begin to separate Diakinesis o Chromatids continue to separate, non-sister chromatids attached via chiasmata moving towards ends of tetrad= terminalization, and nuclear envelope starts to break down

8. Compare and contrast cell division in prokaryotes and eukaryotes.  

Prokaryotic cells divide by binary fission Eukaryotic cells divide by mitosis (karyokinesis) and cytokinesis

9. Explain what happens in the different phases of the Cell Cycle       

Cell cycle consists of four phases: G1, S, G2, and M. Together, G1, S, and G2 phases are known as interphase. In M (mitosis) phase, chromosomes are partitioned to two sides of the cell and the cell divides into two daughter cells. In G1 (first growth) phase, cell grows and synthesizes proteins. In S (synthesis) phase, cell replicates its DNA; the chromosomes are duplicated. In G2 (second growth) phase, cell grows further and prepares for mitosis. Non-dividing cells can also enter into a special G0 phase. The cell cycle is controlled at three checkpoints through the interaction of cyclins with cyclindependent kinases (Cdks) 1. The integrity of the DNA is assessed at the G1 checkpoint. 2. Proper chromosome duplication is assessed at the G2 checkpoint. 3. Attachment of kinetochores to spindle fibers is assessed at the M checkpoint.

10. Describe the differences between cytokinesis in animal cells as compared to plant cells.  

During cytokinesis in ANIMAL cells, a ring of actin filaments forms at the metaphase plate. The ring contracts, forming a cleavage furrow, which divides the cell in two. In PLANT cells, Golgi vesicles coalesce at the former metaphase plate, forming a phragmoplast. A cell plate, formed by the fusion of the vesicles of the phragmoplast, grows from the center toward the cell walls, and the membranes of the vesicles fuse to form a plasma membrane.

11. Describe Mendel’s Postulates   

Pairs of Unit Factors & Dominance: The genotype for a trait is specified by a pair of genes, one from each parent. Traits are determined by dominant and recessive alleles. Law of Segregation: During the formation of gametes, the gene pairs segregate equally. Each gamete receives only one member of the pair and has an equal chance of receiving either one. Recessive alleles are only expressed when they exist in 2 copies, whereas only one copy of a dominant allele is needed to express the trait. 6

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12. Know the roles of cohesin, separase, and Shugoshin in synaptonemal complex formation.    

Cohesin- holds together sister chromatids Separase- separates them by cleaving cohesion Separase cannot cleave cohesion unless it is phosphorylated by kinase Shugoshin- prevents cohesin from being phosphorylated, recruits phosphatase to cohesin sites, protects cohesin from being cleaved

13. Be able to use map distances to determine recombination frequency (and vice versa). How many map units apart? Shown different maps and be asked what is the recombination frequency  The amount of recombination between two genes on the same chromosome is proportional to the distance between them.

14. Explain gene linkage and how it disrupts Mendelian offspring ratios.  When two genes are close together on the same chromosome.  Linkage will affect expected ratios because two genes that are close together on the same chromosome tend to travel as a unit and are not independent of each other.

15. Know how to calculate recombination frequency from recombinant vs parental phenotypes.  (# of recombinant progeny/total # of progeny) x 100 16. Describe the chromosomal theory of inheritance and Thomas Hunt Morgan’s contributions to chromosomal theory and linkage.  theory proposing that chromosomes are the vehicles of genes and that their behavior during 

meiosis is the physical basis of the inheritance patterns that Mendel observed -Confirmed chromosomal theory of inheritance -Showed linear arrangement of genes on chromosomes -Explained "coupling" as genes linked on same chromosome -Demonstrated spontaneous mutations in genome -Identified first X-linked gene: white-eye mutation in fruit flies

17. Compare XY, XO, ZW sex determination modes   

XY- mammals o male: XY ;female: XX XO- Insects o male: XO (X:A ratio 0.5); female: XX (X:A ratio 1.0) ZW- Birds o males: ZZ; females: ZW

18. Explain gene dosage compensation in homogametic sexes and the role of XIST in Xinactivation. 

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All individuals in a species should have same level of gene expression for non-sex determining genes by way of the process called X-chromosome inactivation (XCI), female mammals transcriptionally silence one of their two Xs. The inactivated X chromosome then condenses into a compact structure called a Barr body, and it is stably maintained in a silent state codes for a long RNA that binds to the X chromosome to promote compaction effectively inactivating it

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19. Describe the role of the SRY gene in determining maleness in humans. How can a person be genetically female, but phenotypically male? What about genetically male, but phenotypically female?  -Located adjacent to PAR of the short arm of Y chromosome -Controls male development -Encodes protein: Testis-determining factor (TDF)

20. Be able to explain the 4 genetic consequences of meiosis. (slide)  Reduction of the chromosome number from diploid to haploid, the essential step in the formation of gametes.  Segregation of alleles, at either meiosis I or meiosis II, in accordance with Mendel’s first law.  Shuffling of the genetic material by random assortment of the homologues, in accordance with Mendel’s second law.  Additional shuffling of the genetic material by crossing over, which is thought to have evolved as a mechanism for substantially increasing genetic variation but is, in addition, critical to ensure normal chromosome disjunction. 21. Know how to calculate and interpret the Chi-squared (χ2) statistic to determine the goodness of fit of observed phenotypic data to predicted values for a specific inheritance pattern. 

Module 2

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Complementary gene action- 9 A_B_: 7 A_bb, or aaB_, or aabb X- linked dominant and recessive only apply to females Parent= XLX and XY Late onset= 1 XLX : 1 XLY : 1 XX: 1 XY Early onset= death Autosomal- 1:2:1 Red/green blindness Agouti equals= codominant Bombay phenotype Mitochondrial- maternal inheritance, all children will have it, no male to offspring transmission Heteroplasmy- variation of DNA Could have more than one population of mitochondria, variation in expression Only pedigrees need to know is 5 on study guide Do not use sum rule Paternal transmission bias- when the mutation is transmitted from the father it has a greater chance of becoming a worse disease allele, chance of expansion getting bigger Anticipation- as the allele goes through generations= increased severity and earlier onset Chi squared df based on phenotypes possible Know 5 stages of prophase in meiosis!!!! SRY- region TDF- gene Most mutations- point mutation Dynamic mutation- triplet and doublet repeat mutations, dynamic= changes as it moves through generations At least 3 genes to make a gene map Count F2 to find mode of inheritance

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