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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?


School: Florida Atlantic University
Department: Process Biology
Course: Genetics
Professor: Colin hughes
Term: Spring 2017
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 200 Views 4 Unlocks


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  


▪ 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

∙ 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 Don't forget about the age old question of What is balance in a healthy diet?

∙ 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

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 We also discuss several other topics like What is head to head method?

o M – mitosis and cytokinesis; cell ready to divide


o Spindle-assembly checkpoint – occurs during metaphase in which the  chromosomes are aligning on the spindle-assembly checkpoint

▪ 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

∙ 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 We also discuss several other topics like What are the main features of the anthropological?

o Each newly formed cell contains half of the cytoplasm and organelle content of  original parent cell Don't forget about the age old question of What can i say to raise someone's confidence?

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 We also discuss several other topics like What is the difference between the two primary classifications of interior design?

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


∙ 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 If you want to learn more check out Define life. what are some features that are present in most living organisms?

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


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


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)


∙ 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


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  


∙ 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  


▪ 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


▪ 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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