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FAU / Process Biology / PCB 3063 / What is unicellular with a simple cell structure?

What is unicellular with a simple cell structure?

What is unicellular with a simple cell structure?

Description

School: Florida Atlantic University
Department: Process Biology
Course: Genetics
Professor: Colin hughes
Term: Spring 2017
Tags:
Cost: 50
Name: Exam 1 Study Guide (PCB 3063)
Description: Chapters 2-5, incorporates lecture notes, textbook notes, and questions from end of chapters
Uploaded: 09/05/2017
7 Pages 50 Views 4 Unlocks
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What is unicellular with a simple cell structure?



Exam 1 Study Guide: Chapters 2 – 5  

Chapter 2: Cells, Chromosomes, and Cellular Reproduction 

∙ Prokaryotes vs eukaryotes

o Prokaryotes – unicellular with simple cell structure

▪ Genes are on single, circular DNA molecule, which is considered a  

chromosome

▪ Eubacteria – true; don’t have histones

▪ Archaea – ancient; have histones, but their histone-DNA complexes differ  from that of eukaryotes

▪ Genetic material in close contact with other cell components – no  

membrane-bound organelles

o Eukaryotes – compartmentalized cell structures; can be unicellular or  multicellular


What is compartmentalized cell structures; can be unicellular or multicellular?



▪ Components bound by intracellular membranes

▪ Genes are on multiple, linear DNA molecules

▪ Nuclear envelope develops around genetic material to form nucleus – this  separate DNA from the rest of the cellular content

▪ Histones – DNA tightly packed around this protein We also discuss several other topics like What is variety in a healthy diet?
We also discuss several other topics like What is the direction of magnitude?

∙ Histone-DNA complex forms chromatin structure

∙ All cells reproduction includes three important events, but the processes that lead to these  events differ in prokaryotes and eukaryotes because of their differing cell structures o Cell’s genetic information must be copied

o Copies of genetic information must be separated from one another


What is the meaning of interphase?



o Cell must divide

∙ Prokaryotic reproduction via binary fission

o Circular chromosome replicates and the cell then divides via binary fission o Prokaryotic cell contains single circular chromosome; as the chromosome  replicates, the origins separate to opposite sides We also discuss several other topics like What are the main features of the anthropological?

o Origins are then anchored to opposite sides of cell and the cell divides o Each new cell thus has an identical copy of the original chromosome  

∙ Interphase – extended period between cell divisions where DNA synthesis and  chromosome replication take place; the cell is growing, developing, and functioning o G1 – cells grows and proteins necessary for cell division are synthesized o G0 – cell may enter this phase, which is a stable state during which cells maintain  a constant size

o G1/S checkpoint – holds cell in G1 until cell has all of the enzymes necessary for  DNA replication

▪ After this checkpoint has passed, the cell is committed to divide 

o S – DNA synthesis; each chromosome duplicates

▪ This phase must take place before cell can proceed to mitosis

▪ Each chromosome is composed of two chromatids

o G2 – cell prepares for mitosis (cell division) through series of biochemical events o G2/M checkpoint – passed only if cell’s DNA is completely replicated and  undamaged Don't forget about the age old question of What can i say to raise someone's confidence?

o M – mitosis and cytokinesis; cell ready to divide

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o Spindle-assembly checkpoint – occurs during metaphase in which the  chromosomes are aligning on the spindle-assembly checkpoint We also discuss several other topics like How much time do humans spend indoors?

▪ This checkpoint ensures that each chromosome is aligned to spindle fibers  from opposite poles

▪ Cell passage through this checkpoint depends on tension generated at  kinetochore as the two conjoined chromatids are pulled in opposite  

directions by spindle fibers

▪ Without this checkpoint and without the tension, the individual will have  an abnormal number of chromosomes Don't forget about the age old question of What is biodiversity in simple words?

∙ Mitosis – produces two daughter cells that are genetically identical to each other and the  parent cell; each of the cells produced contain full complement of chromosomes because  there is no net increase/decrease in chromosome number

o Each newly formed cell contains half of the cytoplasm and organelle content of  original parent cell

o Cells are genetically identical because no crossing over took place

o Prophase – each chromosome possesses two chromatids at centromere because  the chromosomes were duplicated in S phase of interphase

▪ Chromosomes condense and mitotic spindle forms

o Prometaphase – nuclear envelope disintegrates and spindle microtubules anchor  to kinetochores

▪ When end of microtubule encounters kinetochore, microtubule becomes  stabilized; eventually, each chromosome becomes attached to  

microtubules from opposite spindle poles

▪ Spindle microtubules are composed of tubulin subunits that are polar,  meaning they have + and – ends

∙ + end is oriented away from centrosome, - end is oriented toward  

centrosome

∙ Microtubules will lengthen and shorten at either the + or – end

o Metaphase – chromosomes align on spindle-assembly checkpoint where the  chromosomes arrange on metaphase plate, which is between the two centrosomes ▪ Spindle-assembly checkpoint must be passed in order to have the proper  number of chromosomes at the end of mitosis

o Anaphase – sister chromatids separate, becoming individual chromosomes that  migrate toward spindle poles

▪ Molecular motors are special proteins that disassemble tubulin molecules  from spindle and generate forces that pull chromosome toward spindle  pole

o Telophase – chromosomes arrive at spindle poles, nuclear envelope reforms  around each chromosome set, and condensed chromosomes relax

▪ Cytokinesis (division of cytoplasm) then follows

∙ Meiosis – production of haploid gametes, otherwise known as germ cells (eggs, sperm);  meiosis reduces the number of chromosomes and produces genetic variation through  recombination of genes (crossing over, independent assortment of chromosomes)

o Each original cell produces four haploid cells because it reduces the number of  chromosomes by half in each cell; the four cells are genetically different from

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each other because of crossing over (Prophase I), random alignment (Metaphase  I), and random distribution (Anaphase I)

▪ The number of possible combinations is 2n, where n is the number of

homologous pairs

▪ Crossing over shuffles alleles on same chromosome into new  

combinations; random distribution of maternal and paternal  

chromosomes shuffles alleles on different chromosomes into new  

combinations – produces genetic variation

o Interphase – DNA synthesis and chromosome replication

o Meiosis I – separation of homologous chromosomal pairs, reduction in  chromosome number by half

▪ Prophase I – five sub-stages

∙ Leptotene – chromosomes contract and become visible

∙ Zygotene – chromosomes continue to condense; homologs pair up  

and begin synapsis, which is the close pairing association between  

homologous chromosome pairs

∙ Pachytene – chromosomes become shorter and thicker, and a three

part synaptonemal complex develops between homologs (tetrad)

∙ Diplotene – centromeres of paired chromosomes move apart; the  

two homologs remain attached at chiasm, which is the result of  

crossing over

∙ Diakinesis – nuclear envelope breaks down, spindle forms

▪ Metaphase I – random alignment of homologs along metaphase plate

∙ Random alignment contributes to genetic variation because it leads  

to new combination of traits; orientation of each tetrad is random

∙ Alignment occurs differently in every meiosis phase

▪ Anaphase I – homologous pairs separate; random distribution of  

chromosomes into two newly divided cells

∙ Sister chromatids remain attached and travel together

▪ Telophase I – chromosomes arrive at spindle poles and cytoplasm divides o Interkinesis – period of rest between meiosis I and meiosis II; nuclear envelope  reforms, spindle breaks down, chromosomes relax

▪ When cells enter Prophase II, the events of interkinesis are reversed

o Meiosis II – separation of sister chromatids (AKA equational division) ▪ Meiosis II is very similar to mitosis because it is separating sister  

chromatids into separate cells; it’s referred to as equational division  

because the number of chromosomes in each new cell is unchanged  

compared to the number of chromosomes in parent cell (like mitosis)

▪ Prophase II – chromosomes re-condense

▪ Metaphase II – individual chromosomes line up on metaphase plate

▪ Anaphase II – sister chromatids separate and move toward opposite poles ▪ Telophase II – chromosomes arrive at spindle poles and cytoplasm divides Chapter 3: Basic Principles of Heredity 

∙ Mendel’s approach of studying heredity

o Used Garden peas to study heredity, which made his study very successful

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o Peas – inexpensive, easy to cultivate, many progeny, diploid, sexually  reproducing, grow rapidly

▪ Can complete an entire generation in single growing season, which  

allowed Mendel to follow the inheritance of individual characteristics for  multiple generations

▪ Seven characteristics with no linkage – seed color/shape/coat color, pod  color/shape, flower position, stem length

∙ Each characteristic has two forms/alleles, one of which is dominant

∙ Genotype – set of alleles an organism possesses; determines potential for development by  setting certain limits on that development

o A given phenotype arises from a genotype that develops within a particular  environment

∙ Phenotype – physical manifestation; organisms DO NOT transmit their phenotype to the  next generation (phenotype is not inherited)

o Only the alleles of genotype are inherited

∙ Principle of segregation – alleles separate during gamete formation, with each gamete  receiving only one allele

o Each diploid individual has two alleles for any characteristic because one allele is  inherited from each parent

o The two alleles segregate when gametes formed, separated in equal proportions ∙ Dominant – when the two alleles are heterozygous, only the trait encoded by one of them  (the dominant allele) is observed

∙ Multiplication rule – probability of two or more independent events taking place together  is calculated by multiplying their independent probabilities

o Outcomes of one event must not influence the other

∙ Additional rule – probability of any one of two or more mutually exclusive events is  calculated by adding the probabilities of these events

o Mutually exclusive – two or more events that cannot occur simultaneously ∙ Chromosome theory of heredity – genes are found on chromosomes

o Each homologous chromosomal pair consists of a paternal and maternal  chromosome

o These pairs segregate into gametes during meiosis, which is the biological basis  of Mendelian principles of heredity

∙ Principle of segregation (Mendel’s first law) – two alleles of certain locus  separate/segregate into different gametes

o Every gamete only receives one allele of each gene

o Occurs during prophase I

∙ Principles of independent assortment (Mendel’s second law) – when two alleles separate,  separation is independent of the separation/segregation of alleles at other loci o Alleles sort into gametes independently – independent events

o Occurs during anaphase I

Chapter 4: Sex Determination and Sex-Linked Characteristics 

∙ Fundamental difference between males and females – gamete size

o Males produce countless amounts of small sperm, females produce limited  amount of large gametes

∙ Monoecious organisms have both male and female reproductive features (flowers)

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∙ Dioecious organisms have male or female reproductive features, in which sex must be  determined – chromosomes, genetics, or environments

o Sex determination – mechanism by which sex established

∙ XX-XO system of sex determination – used in insects such as grasshoppers o Only one sex chromosome present, which is the X chromosome

o Males are XO, having only one X chromosome (heterogametic)

o Females are XX, having two X chromosomes (homogametic)

∙ XX-XY system of sex determination – used in humans o Males are heterogametic, XY

o Females are homogametic, XX

Autosomes – non-sex  chromosomes

o Sex determined by the presence of Y chromosome, which is inherited from father o Y chromosome is acrocentric; X and Y are not homologs of each other, but they  do pair and separate during meiosis

▪ Are able to pair because of pseudo-autosomal regions – areas where X and  Y carry the same genes

o ZZ-ZW system of sex determination – use in birds, fish, amphibians ▪ Similar to XX-XY system; however, females are heterogametic while  males are homogametic

▪ Females – ZW, Males – ZZ

∙ Sex determination in Drosophila (fruit fly) – have eight chromosomes, three pairs of  autosomes and one pair of sex chromosomes

o Sex determined by balance (X:A ratio ) between female- and male-determining  genes on X and Y chromosomes, respectively

o X:A ratio – X chromosomes divided by number of haploid sets of autosomes;  predicts the sexual phenotype

▪ X:A = 1 ???? Female, X:A > 1 ???? meta-female

▪ X:A = 0.5 ???? Male, X:A < 0.5 ???? meta-male

▪ X:A between 0.5 and 1 ???? intersex

o Normal flies have two haploid sets of autosomes and either: two X chromosomes  or one Y chromosome

o System similar to humans in that XX codes for female and XY for male o X:A ratio predicts phenotype; however, sex determined by genes on X in fruit  flies while sex determined by genes on Y in humans

∙ X-linked traits

o Females – if she expressed X-linked recessive trait, then her father also expressed  it and mother was carrier

o Males – cannot inherited X-linked traits from father

▪ Show phenotypes of X-linked trait, it doesn’t matter if allele is recessive  or dominant

▪ Inherit traits from mothers, pass traits to daughters not sons (will pass on  to their grandsons)

∙ Y-linked traits – only inherited by males, always inherited from father ∙ Nondisjunction – failure of homologous chromosomes/sister chromatids to separate  during division, resulting in abnormal distribution of chromosomes in new cells o Failure occurs during Anaphase I, the homologous chromosomes are pulled to the  same pole instead of separating

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o Bridge’s study of eye color in Drosophila showed this – white-eyed females  inherited two X chromosomes from white-eyed mothers as a result of  

nondisjunction

∙ Dosage compensation

o Females – have two copies of X chromosomes and two copies of each autosome;  sex chromosomes and autosomes are in balance

o Males – have one X and two copies of each autosomes; there is less protein  encoded by X-inked genes than proteins encoded by autosomal genes (imbalance) o Imbalance corrected through use of dosage compensations, which equalize the  amount of protein produced by single X and two autosomes in heterogametic sex o Dosage compensation in mammals done via inactivating one of X chromosomes  in females (which X is inactivated is chosen randomly) – Barr bodies

o Barr bodies – condensed, darkly staining bodies in nuclei of cells; are the inactive  X chromosomes (Lyon hypothesis)

▪ Neighboring cells have same X inactivated ???? produces patchy pattern for  X-linked characteristic expression in heterogametic females

▪ Patchiness can be seen in tortoise shell and calico cats

▪ Once an X is inactivated, it remains inactive – all somatic cells produced  from this cell are also inactive

▪ Number of Barr bodies is one less than the number of chromosomes

▪ Males – hemizygous, may be black or orange but never two colors  

simultaneously

▪ Females – black, orange, or tortoiseshell; each patch of orange or black is  a close of cells that derive from original cell in which orange or black  

allele is inactivated

Chapter 5: Extensions and Modifications of Basic Principles 

∙ Incomplete dominance – heterozygote phenotype is intermediate between phenotypes of  the two homozygotes

o Can be explained by Mendelian genetics of segregation of alleles

∙ Codominance – heterozygote phenotype includes phenotypes of both homozygotes o Joint production of both products in heterozygote

o Heterozygote expresses phenotypes of both homozygotes at same time ∙ Penetrance – percent of individuals with certain genotype that express associated  phenotype

o Incomplete penetrance – genotype doesn’t always produce expected phenotype ∙ Expressivity – degree to which trait expressed

∙ Incomplete penetrance and expressivity due to other genes and environmental factors ∙ Gene interaction – genes at different loci (not allelic) help determine single phenotypic  characteristic; products of genes at different loci combine to make new phenotypes o Epistasis – masking of expression of one gene by another at different locus ▪ Similar to dominance, but dominance masks genes at same locus

o Epistatic gene – gene that does masking

o Hypostatic gene – gene whose effect is masked

o Recessive epistasis – two recessive alleles inhibit allele expression at different  locus

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▪ Example: varying coat colors of Labrador Retrievers determined by gene  interactions at two loci (black, brown, deposition, no deposition)

∙ One loci codes for pigment produced by skin cells while the other  

affects pigment deposition in hair shaft

∙ Complementation test – tests if mutations in two strains are in different genes o Complementation won’t occur if mutations are in same gene; has taken place if  individual possessing two recessive mutations has wild-type phenotype, which  indicates that mutations are not on same locus (non-allelic)

o No complementation occurs when two recessive mutations occur at same locus – mutant phenotype produced

∙ Cytoplasmic inheritance – some genetic material encoded by genes in cytoplasm, which  leads to cytoplasmic inheritance

o Zygote will inherit nuclear genes from both parents; however, cytoplasmic genes  inherited from only one gamete (usually egg)

o Extracellular genes found in chloroplasts or mitochondria

o Genes for a trait are inherited from only one parent

∙ Genetic Maternal Effect – offspring’s phenotype determined by mother’s genotype o Genes inherited from both parents, but offspring’s phenotype determined by  mother’s genotype, not by its own genotype

∙ Genomic imprinting – form of epigenetics; differential expression of genes depends on  whether genes are inherited from mom or dad

∙ Anticipation – not explain by Mendelian genetics; traits become strongly expressed at  earlier stage as they’re passed on through generations

o Traits that show anticipation have mutant alleles that are unstable, which change  through each generation

o Caused by trinucleotide repeats; as repeats increase, so does anticipation Review applied problems at end of chapter for better conceptual understanding

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