Unit 4 (study buddy)

Question 1

what does DNA stand for?

Answer 1

Deoxyribonucleic acid

Question 2

explain the structure of DNA

Answer 2

• double helix
• chain of nucleotides (sugar-phosphate backbone and nitrogenous bases)
• complementary base pairing (A-T, G-C)
• weak, base-specific hydrogen bonds between DNA strands

Question 3

Explain the role of helicase and DNA polymerase in process of DNA replication

Answer 3

• HELICASE is enzyme that unwinds double helix to separate nucleotide pairs by breaking hydrogen bonds
• DNA POLYMERASE is enzyme that moves along strand, reading, matching, and attaching corresponding free-floating nucleotides
• DNA POLYMERASE only works in 5’ –> 3’ direction
• therefore leading (works in same direction helicase unwinds) and lagging (works in opposite direction to helicase, so does portion, stops, moves to new unwound portion, etc.) strands

Question 4

describe process of meiosis I and II

Answer 4

MEIOSIS - special type of mitosis that produces gametes

MEIOSIS I:
- PROPHASE I (c’somes condense, homologous c’some pairs align and exchange sections of DNA (crossing over); there are 4 chromatids and 2 chromosomes)
- METAPHASE I (bivalent c’somes align at equator, centrioles produce spindle fibres that attach to centromeres of c’somes)
- ANAPHASE I (spindle fires shorten, pulling away pairs of sister chromatids towards poles, cell elongates)
- TELEPHASE I (c’somes arrive at poles, spindle fibres dissolve, new nuclear membranes form, cytokinesis –> 2 daughter cells)

MEIOSIS II:
- same steps of meiosis I repeated, but:
METAPHASE II (single chromosomes (pair of chromatids) line up in middle)
ANAPHASE II (chromatids pulled apart)
TELEPHASE II (now there are 4 gametes with 23 c’somes)

Question 5

describe processes of crossing over and recombination in regard to genetic variation

Answer 5

• crossing over - exchange of sections of DNA between homologous chromosome pairs during prophase of meiosis I
• part of process of unique chromosome production call recombination

Question 6

compare and contrast process of spermatogenesis and oogenesis

Answer 6

SIMILARITIES:
- result in haploid gametes that are genetically variable
- occur in gonads
- processes controlled by hormones

DIFFERENCES:

LOCATION (spermatogenesis –> all completed in testes; oogenesis –> begins in ovaries, completed in fallopian tube)
COMPLETION (s –> division completed regardless of fertilisation; o –> meiosis II only completed if fertilisation occurs)
NO. CELLS (s –> all 4 daughter cells become sperm; o –> only 1 daughter cell becomes an egg, others become polar bodies)
TIMING (s –> continuous process from onset of puberty; o –> begins during foetal development, pauses until puberty, stops at menopause)
SPECIALISATION (s –> smaller, motile, tail, high mitochondrial numbers; o –> larger, non-motile, nutrient storage levels are high)

Question 7

Define the terms ‘gene’ and ‘genome’,

Answer 7

GENE - section of DNA that codes for proteins; inherited from parent to offspring
GENOME - complete set of all gene-containing chromosomes an individual carries in cells

Question 8

Describe coding and noncoding genes

Answer 8

CODING GENES:
- code contained in nucleotide triplet –> codon
- each codon corresponds to an amino acid

NONCODING GENES:
- production of functional RNA
- regulating gene expression (control structural genes)
- centromeres (points of attachment of chromatids)
- telomeres (endcaps of each c’some)
- introns (non-coding DNA within split gene)
- many functions yet to be determined

Question 9

Explain process of transcription

Answer 9

• process that occurs in nucleus of eukaryotic cells
• allows single-stranded mRNA molecules to be produced from double-stranded DNA

INITIATION:
- RNA polymerase unzips DNA double helix by breaking hydrogen bonds between bases
- this exposes based, allowing them to bind with free gloating nucleotides during elongation

ELONGATION:
- RNA polymerase moves along exposed DNA strand, using it as a template to build mRNA strand from free-floating nucleotides
- synthesis of mRNA follows same base pairing as DNA, except A now pairs with U

TERMINATION:
- stop codon signals RNA polymerase to cease transcription and terminate mRNA molecule

Question 10

Explain the process of translation

Answer 10

• ribosomes build polypeptide chain from amino acids by translating mRNA codons

INITIATION:
- ribosomal subunit attaches itself and moves along mRNA strand until it recognises a start codon
- free-floating transfer RNA (tRNA) molecule with corresponding anticodon attaches to mRNA start codon –> now ready to begin translating

ELONGATION:
- as ribosome progresses along mRNA strand, it reads codons and matches them with anticodon of nearby tRNA molecules
- as each tRNA anticodon binds with corresponding mRNA codon, it release its amino acid, which joins growing polypeptide chain through condensation polymerisation reaction

TERMINATION:
- ribosome reads stop codon and releases polypeptide chain into cytoplasm
- free-floating polypeptide chain them moves to endoplasmic reticulum or Golgi apparatus where it will undergo further processing to become a functional protein

Question 11

Describe factors that regulate gene expression

Answer 11

1. REGULATION THROUGH PRODUCTS OF OTHER GENES
   - regulatory genes –> control expression of other genes
   - eg. repressors that stop production of protein coded on another gene
2. REGULATION DURING TRANSCRIPTION
   - histone acetylation/methylation:
   • if DNA is loosely bound around histones (acetylation), DNA is more easily copied
   • if DNA is more tightly bound around histones (methylation), it is more difficult to copy
   • these processes act like a dial

• DNA acetylation/methylation:
  
  • chemical tag (methylation) added to DNA to “switch off” gene
  • alternatively, tag is removed (acetylation) to “switch on” gene

3. REGULATION DURING TRANSLATION
   - mRNA binding proteins –> some proteins can bind to mRNA blocking translation process
   - micro RNA –> short fragments of RNA can bind with mRNA and interfere with translation
4. REGULATION VIA ENVIRONMENTAL EXPOSURE
   - epigenome incorporates environmental exposures outside the cell
   - factors such as diet, diurnal and seasonal changes, exposure to meds, disease and chemicals can influence expression/repression of genes

Question 12

Describe transcription factors and Hox genes

Answer 12

• transcription factors determine when and where genes are expressed
  Hox genes control position of body structures along head to tail axis

Question 13

Explain gene mutations and how they can occur

Answer 13

• mutation is a change in DNA sequence that results in different version of a gene (i.e. allele)
• can be change of single nucleotide base pair, or changes to entire genes or chromosomes

POINT MUTATIONS:
- change to single nucleotide base
- can change amino acid added to polypeptide chain
- substitution, nonsense mutation, insertion frameshift, or deletion frameshift

NON-DISJUNCTION:
- occurs when spindle fibres fail to separate chromatids during anaphase (can occur in meiosis I or II, or mitosis)
- daughter cells have abnormal no. chromosomes –> referred to as ANEUPLOIDY

DAMAGE BY MUTOGENS:
- mutations can be caused by mutagens (eg. UV radiation, ionising radiation, heat, or chemicals)

SOMATIC MUTATIONS:
- mutations withing somatic cells, so will only affect individual because DNA is not passed to offspring

INHERITED MUTATIONS:
- mutations in germ line cells (sperm and egg), which are passed on to offspring

Question 14

explain karyotypes

Answer 14

• karyotype is an image of an individual organism’s complete set of chromosomes in their homologous pairs
• average human has 23 c’somes –> 22 somatic and XX (female) or XY (male)

Question 15

Explain alleles, genotypes, and phenotypes (in regards to inheritance)

Answer 15

ALLELES:
- different versions of genes
- can be dominant or recessive
- in diploid cells, there are 2 of each chromosome, so the dominant will be expressed
GENOTYPES = allele organism carries for a particular trait
PHENOTYPES = describes the trait expressed

Question 16

describe frequency histograms (in regards to inheritance and phenotypes)

Answer 16

• provide visual representation of selected trait frequencies in population/species
• commonly produced with discrete traits such as allele presence, genotype, or phenotype on x-axis, and frequency on y-axis

Question 17

describe punnett squares

Answer 17

• tool used to predict all possible genotypes and phenotypes of offspring of known parents
• it is possible to predict probability of genotypes and phenotypes when allele dominance is known

DRAWN WITH FOLLOWING FEATURES:
- alleles of one parent on top, and alleles of other parent on side
- corresponding combinations of alleles written in spaces aligning with parents’ alleles
- percent geno/pheno determined

Question 18

describe autosomal dominance

Answer 18

• dominance exhibited by any chromosome other than a sex chromosome causing traits or conditions to be expressed in pheno. of the organism

Question 19

describe sex-linked inheritance

Answer 19

• X and Y carry genes for traits other than biological sex, and have different pattern of inheritance from those of autosomal genes

EXAMPLES OF DIFFERENT TYPES OF SEX-LINKED INHERITANCE:
- X-LINKED RECESSIVE - since males have 1 copy of X c’some, X-linked recessive are more likely to appear in males than females
- X-LINKED DOMINANT - higher prob. of appearing in general pop.
- Y-LINKED INHERITANCE - Y c’some is smaller (less genes), so Y-linked inheritance is rarely seen
- SEX-LIMITED INHERITANCE - some traits only appear in one sex –> if genotype that affects male trait is carried by female, it will not be expressed since male characteristic is absent in females

Question 20

explain phenotypic characteristics of multiple alleles and explain polygenic inheritance

Answer 20

MULTIPLE ALLELES
- when more than 2 alleles control a pheno.
- eg. blood type –> 3 alleles, 4 possible pheno. (A, B, AB, O) –> A and B are dominant over O, so both A and B can be expressed if both present

POLYGENIC INHERITANCE:
- some pheno. traits have many variations between 2 extremes (eg. height or skin colour)
- traits controlled by multiple genes
- effect of dominance and segregation still apply, and combined contributions result in wide range of phenotypic possibilities

Question 21

isolation, insertion, joining, amplification

describe process of making recombinant DNA (4 steps)

Answer 21

RECOMBINANT DNA:
- DNA strand containing genetic sequence artificially inserted in laboratory
- goal is to move target gene from donor organism into vector organism

ISOLATION
- target gene is identified in donor organism and isolated using restriction enzyme that cuts DNA at specific base sequence called recognition site
- isolated DNA fragment left with sticky end, allowing it to be joined to corresponding exposed DNA sequence in plasmid of vector organism

INSERTION:
- plasmid (circular molecule of DNA found in cytoplasm of bacteria) of vector organism is cut with same restriction enzyme used on target gene
- target gene is added to plasmid to allow for joining to occur at sticky ends of both molecules

JOINING:
- sticky ends of target gene join according to matching base pairs and enzyme called DNA ligase glues segments of DNA together to form complete and continuous DNA segment

AMPLIFICATION:
- bacteria containing recombinant plasmid are allowed to replicate, producing millions of copies of target gene to allow for mass production of desired protein

Question 22

recognise applications of DNA sequencing to map genomes and DNA profiling

Answer 22

• DNA sequencing allows DNA and protein sequences to be analysed and interpreted
• this tech. allows detailed info about genes, and how they work
• genome mapping involves determining locus of a gene on a c’some and the relative location of a gene in relation to others
• mapping this info assists scientists when working on treatments for genetic diseases

Question 23

explain polymerase chain reaction (PCR)

Answer 23

• technique for amplifying small samples of DNA

DENATURATION:
- temp. of sample raised to 95°C to break hydrogen bonds between DNA nucleotides, creating 2 single-strands
ANNEALING:
- temp. lowered to below 60°C, allowing primers to bind (anneal) to start of DNA sequence
EXTENTION:
- temp. raised to 72°C, allowing Taq polymerase to attach to primers and add free-floating nucleotides as it moves along exposed sequence, creating double stranded DNA

• repeat for many cycles, exponential growth, millions of copies made

Question 24

explain gel electrophoresis

Answer 24

• procedure to separate fragments of DNA according to size, allowing samples from different indiv. to be compared
• samples placed in gel that has electric current
• DNA has -ve charge, so moves towards +ve end
• smaller molecules move through gel further than larger
• used to compare samples from crime scenes to suspects, or sample from child to possible fathers to find paternity

Question 25

define terms ‘evolution’, ‘microevolution’, and ‘macroevolution’

Answer 25

EVOLUTION:
- process of change of population over time, over successive generations in response to selection pressures
- presence of these adaptations allow organism to better respond to environment and help survive and have more offspring

MICROEVOLUTION:
- changes in allele frequency in population that gives those with more suitable phenotypes an evolutionary advantage

MACROEVOLUTION:
- accumulation of multiple microevolutionary changes that results in permanent change in species’ phenotype over long period of time

Question 26

explain evolutionary radiation and mass extinction

Answer 26

EVOLUTIONARY RADIATION:
* increase in taxonomic diveristy caused by high rates of speciation from common ancestor

MASS EXTINCTIONS:
- extinciton sof vast number of species within short geological time frame
- usually correlate with catastrophic global events or widespread environ. changes that occur too rapidly for majority of species to adapt
- have great impact on biodiversity

Question 27

explain natural selection

Answer 27

NATURAL SELECTION:
- describes ability of individuals with advantageous phenotypes to overcome selection pressures, and survive long enough to reproduce and pass on advantageous alleles

VIABILITY:
- physical characteristics, metabolic process, and behaviours more suited to environment and increase changes of survival

FUCUNDITY:
- refers to max. number of offspring indiv. is capable of producing across lifespan
- r-strategists produce thousands of offspring, so have higher fecundity than K-strategists

Question 28

describe how allele frequency in gene pool can be +ve or -ve

Answer 28

• allele frequency in pop. determined by selection pressures
• may be positively or negatively selected for –> may increase or decrease in frequency

Question 29

explain 3 main types of phenotypic selection

Answer 29

STABILISING SELECTION:
- stable environments maintain species’ consitency over time
- continue to be selected for same narrow range of alleles, leading ot reduced allele variation at extremes of tolerance range
- graph becomes taller and more narrow in middle of tolerance range

DIRECTIONAL SELECTION:
- pop. must adapt to new slection pressures when environ. changes
- resulting shift in frequency new new advantageous pheno. is called direcitonal selection
- graph moves with peak to one of the extreme ends of tolerance range

DISRUBPTIVE SELECTION:
- sometimes environ. factos change suddenly, and individuals at extemes find advantage over average
- graph moves to be bimodal –> 2 peaks at extremes of tolerance range

Question 30

explain microevolutionary change through genetic drift
(population bottleneck and the founder effect)

Answer 30

• for various reasons, not all indiv. are able to contribute genes to next gen. –> random changes occur in allele frequencies in pop.
• these random changes refered to as genetic drift
• in small, inbreeding populations, genetic drift may have pronounced effects on allele frequencies (alleles may become lost from gene pool or fixed as only allele present)

POPULATION BOTTLENECKS:
- populations may be reduced to low numbers through periods of seasonal climatic chagne, heavy predation or disease, catastrophic natural disasters, etc.
- as result, only small number of individuals remain in gene pool to contribute to next gen.
- this small sample is often not representative of original allele frequencies
- in addition to bottleneck effect, small surviving pop. is often affected by inbreeding and genetic drift

FOUNDER EFFECT:
- small number of indiv. migrate away and become isolated from orig. pop.
- this colonising/founder pop. will have small, probably non-represenative same of alleles from parent pop. gene pool
- as result of founder effect, colonising pop. may evolve in different direction than parent pop.

Question 31

explain microevolutionary change through gene flow

Answer 31

• movement of genes into or out of pop. (immigration and emigration)
• pop. may gain or lose alleles
• tends to reduce differences between populations because gene pools become more similar

Question 32

explain the 4 main patterns of species diversification

Answer 32

DIVERGENT EVOLUTION:
- descendants of common ancestor develop genetic differences in response to differing environ. pressures, resulting in 2 different species

CONVERGENT EVOLUTION:
- unrelated species develop similar phenotypic traits in response to same environmental pressures

PARALLEL EVOLUTION:
- descendents of common ancestor species diverge, then develop similar features independently of each other in response to similar environ. pressures
- usually in different continents

COEVOLUTION:
- simultaneous evolution of 2 species interacting closely with each other
- each species exerts selection pressure on the other, and other responds in turn, perpetuating process of coveolution
- often become dependent on each other

Question 33

describe different mechanisms of isolation that influence gene flow

Answer 33

GEOGRAPHIC ISOLATION:
- populations of species separated by physical geographic barriers (eg. mountains, deserts, water)
- separated pop. unable to breed with each other, limiting diveristy of alleles

REPRODUCTIVE ISOLATION:
- occurs wehn morphological or behavioural barrier prevents individuals from breeding and produing offspring

SPATIAL ISOLATION:
- when distance between populations of species prevents indiv. from breeding accross populations

TEMPORAL ISOLATION:
- when pop. of species reproduce at different times of day or in different seasons

Question 34

Describe modes of speciation

Answer 34

ALLOPATRIC:
- caused by geographic isolation of pop., preventing breeding between 2 groups
- over time, 2 separated groups evolve differently with selection pressures, and eventually become different species
- evolution in isolation

SYMPATRIC:
- occurs when populations remain in same geographic area, but are subject to varying selection pressures caused by differing local environ. conditions
- variation in environ. conditions causes populations in same area to adapt, isolating them from other half of pop.
- evolution within the population

PARAPATRIC:
- occurs where populations occupy same geographic area but tend to breed with individuals in close proximity
- over time, individuals may become pheno. different enough that interbreeding is not possible
- evolution in adjacent niche (still overlap and some access)