Unit 3: Genetics Flashcards

1
Q

Compare and contrast the structure of DNA vs RNA.

A

Both are polymers made of nucleotides in the shape of strands
However,
DNA is double stranded, RNA is single stranded
DNA contains the sugar deoxyribose (Deoxyribose Nucleic Acid = DNA), RNA contains the sugar ribose (Ribose Nucleic Acid = RNA)
DNA has bases of A, T, G, C, but RNA has the bases A, U, G, C
DNA forms a helix with it’s complementary bases while RNA does not

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2
Q

Define nucleotides.

A

The basic building block of nucleic acids such as DNA and RNA
Composed of a pentose sugar, a nitrogenous base and a phosphate group
The pentose sugar + nitrogenous base is a nucleoside

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3
Q

State the complementary base pairing rule.

A

Adenine (A) always pairs with Thymine (T)
Guanine (G) always pairs with cytosine (C)

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4
Q

State Chargaff’s rule.

A

The ratio of purines to pyrimidines must be equal
More specifically,
% of A = % of T
% of G = % of C
(A and G are purines, T and C are pyrimidines)

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5
Q

State the 7 main components of DNA replication.

A

Helicase
Single Strand Binding (SSB) proteins
Gyrase
RNA primase
DNA polymerase III
DNA polymerase I
DNA ligase

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6
Q

Describe the function of helicase, SSB proteins and gyrase in DNA replication.

A

Helicase: unwinds strands by breaking the hydrogen bonds

SSB proteins: bind to DNA strands after helicase separation to prevent them from re-annealing (rewinding into a helix)
These fall off once replication is complete

Gyrase: reduces torsional strain created when helicase unwinds DNA

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7
Q

Describe the function of DNA/RNA primase, DNA polymerase III, DNA polymerase I, DNA ligase. Include Okazaki fragments in your explanation.

A

RNA primase (aka DNA primase): binds to exposed DNA strand and generates a short RNA primer with a length of ~10-15 nucleotides

DNA polymerase III: binds to the RNA primer and extends it to create a complementary strand; this is required as DNA polymerase can extend a nucleotide chain but not start one
On the leading strand, DNA pol III moves towards the replication fork (spot where strands disconnect) and continuously synthesizes
On the lagging strand, DNA pol III moves away from the replication fork and must synthesize discontinuously
This occurs because DNA pol III can only synthesize in the 5’-3’ direction

DNA polymerase I: the lagging strand has multiple RNA primers placed in order to repeatedly initiate synthesis via DNA pol III
DNA pol I removes the RNA primers and replaces them with DNA nucleotides
These repeated pieces are called Okazaki fragments

DNA ligase: joins Okazaki fragments together by joining sugar-phosphate backbones together with a phosphodiester bond

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8
Q

What did Meselson and Stahl prove about DNA replication, and how did they prove this?.

A

That DNA replication is semi-conservative; each new piece of DNA consists of one old strand and one new strand

Other, disproved methods of replication:
Dispersive: the new DNA alternates between new and old DNA
Conservative: the new strand is completely brand new

Process:
- E. coli was cultured in the presence of a heavy nitrogen isotope, N-15
- It was transferred to a medium with a lighter isotope, N-14
- After taking DNA samples several generations later, they subjected the samples to caesium chloride equilibrium density gradient centrifugation
- This formed lines on test tubes based on the weight of the sample - N-14 drawing a higher line, N-15 drawing a lower line
- Testing of the first generation resulted in a line down the middle of the N-14 and N-15 sections, disproving conservative (which would have one strand at N-14 and one at N-15)
- Testing of the second generation resulted in a line at the N-14 level and one between N-14 and N-15, disproving dispersive (which would only have one band at the level between N-14 and N-15)
- Thus, they concluded DNA replicated semi-conservatively

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9
Q

Define template/antisense strand, coding/sense strand, and mRNA strand, in the context of DNA transcription.

A

The mRNA strand is the strand that copies, or transcribes, the template/antisense strand
The other DNA strand, the one that is not copied but rather attached to the antisense strand is called the sense strand
The sense strand and the mRNA strand are sequentially equal, as they are both complementary to the antisense strand, but the mRNA strand has a U for every T in the sense strand

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10
Q

State the three phases of DNA transcription.

A

Initiation, elongation, termination

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11
Q

Describe the initiation phase of DNA transcription.

A

RNA polymerase binds to a promoter site, a site on DNA that indicates the start region of transcription

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12
Q

Describe the elongation phase of DNA transcription.

A

RNA polymerase moves along the coding region in the 5’-3’ direction
As it does so, it uncoils the DNA and synthesizes an mRNA complementary to the antisense strand

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13
Q

Describe the termination phase of DNA transcription.

A

The RNA polymerase unbinds from the DNA once it reaches and recognizes a terminator site
The sense and antisense DNA strands then re-anneal, or reconnect

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14
Q

Describe the concept of post-transcriptional modifications, when they are used, and provide two examples.

A

Prokaryotes do not need post-transcriptional modifications after DNA transcription, but eukaryotes do
Eukaryotes need post-transcriptional modifications to protect the newly transcribed mRNA molecule from conditions and enzymes outside the nucleus
Two major examples include:
Poly-A tail: a chain of adenine nucleotides to protect the mRNA from enzymes in the cytosol
5’ cap: a sequence of seven guanines placed on the 5’ end that are recognizable by ribosomes

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15
Q

Describe how small nuclear ribonucleoproteins (snRNP’s) remove introns, and include exons in your explanation.

A

Small nuclear ribonucleoproteins (snRNP’s) remove introns without cutting any nucleotides from the exons
Spliceosomes are when snRNPS attach to DNA
The snRNP’s recognize the intron areas and loop them such that the adjacent exons are touching
The spliceosomes are activated and cut the intron off of the DNA strand, where it loops back on itself and eventually degrades
The spliceosome also links the now-touching exons together

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16
Q

State the codon that signals the start of protein translation.

A

AUG, corresponding amino acid methionine (Met)

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17
Q

Define codon.

A

Also known as a triplet, it is a set of three consecutive bases in a DNA or RNA sequence
Together, they code for a singular amino acid

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18
Q

Describe the initiation phase of DNA translation.

A

A small, ribosomal subunit binds to the 5’ end of the mRNA and moves along until it finds the start codon, AUG
The appropriate tRNA molecule, carrying the amino acid Met, binds to the AUG codon
The large ribosomal subunit, which consists of three sites, E, P and A, aligns itself such that the tRNA molecule is in its P (middle) site, and forms a complex with the small subunit

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19
Q

Describe the translocation phase of DNA translation.

A

After elongation, the ribosome moves 1 codon forward
The tRNA that was in the P site has now moved to the E site, and is detached
The next required tRNA molecule comes in and attaches to the unoccupied A site
The bond between the tRNA and its AA is broken and the energy forms a bond between the two adjacent AAs
This process repeats until the termination phase

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20
Q

Describe the termination phase of DNA translation.

A

When the ribosome reaches a stop codon, a release factor is signaled for translation to stop
The polypeptide is released from the ribosome and the ribosome disassembles back into its small and large subunit

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21
Q

Define nucleosomes.

A

Eukaryotic DNA is packaged with histone proteins to created a compact structure called a nucleosome, which help supercoil DNA in order to achieve a more compacted structure that allows for more efficient storage

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22
Q

Outline how the rate of DNA transcription can be increased or decreased.

A

Adding methyl to DNA, a process called methylation, decreases DNA transcription rate:
- Causes nucleosomes to pack tightly together
- Disallows transcription factors to bind to the DNA
- Prevents genes from being expressed

Adding acetyl groups to the DNA strands, a process called acetylation, increases DNA transcription rate:
- Causes looser packing of nucleosomes
- Allows transcription factors to more easily bind to DNA
- Allows genes to be more easily expressed

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23
Q

Define reprogramming.

A

Methylation and acetylation mark the DNA to affect transcription by using markers called epigenetic tags
Since new organisms need unmarked DNA to develop unspecialized, reprogramming involves erasing most epigenetic tags to allow a fertilized egg to properly develop

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24
Q

State the three noncoding regions of DNA.

A

Promoter
Operator
Terminator

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25
Discuss the role of the operator noncoding region in DNA.
Operators are regions that affect the transcription rate of nearby genes There are two sub-regions, called enhancers and silencers - Enhancers increase rate of transcription of corresponding gene when bound to by an activator - Silencers inhibit transcription of corresponding gene when bound to by a repressor
26
Describe PCR and provide one real-world application.
PCR stands for Polymerase Chain Reaction and allows scientists to get vast amounts of DNA by amplifying minute amounts repeatedly Three steps: - Denaturation - DNA sample is heated to separate the two strands - Annealing - Sample is cooled and primers are annealed at the ends strands - Elongation - Sample is heated to the optimal temperature for a heat-tolerant polymerase (Taq) to function - The DNA has now been artificially replicated Taq polymerase is an enzyme from the bacterium Thermus aquaticus It has a high optimal temperature, allowing it to function during the elongation step It is able to extend the nucleotide chain from the primers, allowing the sequence to duplicate Allows for: - Identification of dead - Identifying criminals at crime scenes using minute amounts of DNA - Sequencing the DNA of extinct species and other life forms
27
Define gene, allele, locus, genome, genotype and phenotype.
Gene: small section of DNA that determines a characteristic Allele: a slightly different yet specific variation of a gene Locus: an exact location of a gene Genome: entire genetic information of an organism Genotype: set of alleles you have for a gene Phenotype: the trait you get as a result of the genotype
28
Define autosomal chromosomes and sex chromosomes, and state the amount of chromosomes a human has as well as the sex chromosomes of a female and male human.
Sex chromosomes: chromosomes that determine the sex of an organism XX --> female XY --> male Autosomal chromosomes: chromosomes that are not sex chromosomes Humans have 23 pairs of chromosomes (46 total) 22 pairs are autosomal, last pair is sex chromosomes
29
Define mutations, and state two causes of them.
Mutation: the changing of the structure of a gene, resulting in a new variant Causes: - Mistakes in DNA replication - Exposure to high energy radiation - Exposure to chemicals that might cause mutations (mutagens)
30
Define a base-substitution mutation, and give a prominent example.
A mutation that changes one nitrogenous base in a sequence Example: sickle cell anemia
31
Compare the number of protein-coding genes of: - E. coli (bacteria) - Homo sapiens (humans) - Oryza sativa japonica (rice) - Triticum aestivum (wheat) - Gallus gallus (chicken)
Organism: approx. number of protein-coding genes Bacteria/E. coli: 4000 Humans/Homo sapiens: 20 000 Rice/Oryza sativa japonica: 35 000 Wheat/Tritucum aestivum: 100 000 Chicken/Gallus gallus: 20 000
32
Describe the difference between a person with sickle cell anemia and an unaffected person.
The altered gene is called HBB, located on chromosome 11 This gene codes the beta subunits of hemoglobin, a protein involved in the transport of oxygen The standard, unaffected Hb^A allele reads G A G at the 6th codon of the sense DNA strand The Hb^S allele, the affected one, reads G T G When the HBB locus is transcribed, the mRNA from Hb^A has the codon G A G, which codes for the amino acid (AA) glutamic acid When mRNA transcribes Hb^S, it copies the codon G U G, which codes for the AA valine Hemoglobin formed from glutamic acid is usually the same as that formed from valine, but under certain conditions, such as low oxygen, they behave differently Hemoglobin formed from glutamic acid functions fine Hemoglobin formed from valine gets polymerized into long fibres, significantly reducing its ability to carry oxygen, and changing the shape of the red blood cell to be that of a sickle The shape of the cell clogs blood vessels, causing pain, failure of blood supply and strokes Furthermore, sickled cells are broken down and eliminated by the body, straining the liver by doing so Healthy blood cells must be made, straining bone structure as red blood cells are made from bone marrow
33
Describe the differences between somebody with a heterozygous genotype Hb^A Hb^S, and when it is preferred to somebody with homozygous genotypes Hb^A Hb^A or Hb^S Hb^S
Hb^A Hb^S: cells will only sickle when infected by the parasite that triggers malaria Malaria is killed along with sickled blood cells, offering protection against malaria Preferred genotype in areas with malaria Hb^A Hb^A: no sickling, but no protection from malaria Hb^S Hb^S: cells will sickle under extreme conditions, and offers no protection from malaria
34
Describe prokaryotic DNA (number of copies of genes, name, shape).
DNA only consists of one chromosome, which carries out the entire genome - Only one copy of each gene, unlike in eukaryotes Shape: closed loop, like a rubber band Name: naked DNA, as it is not organized around histone proteins
35
Define a plasmid and where they are found.
Plasmids are found in some prokaryotes as small loops of DNA They may contain genes, which are often related to very specific functions, such as digesting food or resisting a very specific antibiotic Not often found in eukaryotes, with some exceptions (e.g. Saccharomyces cerevisiae)
36
Compare and contrast prokaryotic and eukaryotic DNA.
Prokaryotic DNA takes the form of a closed loop, whereas eukaryotic DNA is long and linear Prokaryotic DNA is not found in a membrane-bound nucleus, whereas eukaryotic DNA is Prokaryotes only contain one copy of each gene, whereas eukaryotes contain two
37
Define chromatin, sister chromatids, centromere, homologous chromosomes/pair and homologue
Chromatin: the form DNA takes on during interphase, when DNA is being actively used Sister chromatids: DNA takes on a X-shape structure during the first stages of mitosis and meiosis; the two lines that form the X are identical copies of the chromosome called sister chromatids - Note that these are renamed to daughter chromosomes after separation (anaphase) Centromere: the place where sister chromatids connect Homologous chromosomes/pair: the two versions of the same chromosome (one inherited maternally, one inherited paternally) Homologue: one chromosome in a homologous pair
38
Compare the genome sizes of: - T2 phage (virus that infects bacteria) - E. coli (common bacterium) - Drosophila melanogaster (fruit fly) - Homo sapiens (human) - Paris japonica (woodland plant)
Organism: genome size, in millions of base pairs T2 phage: 180k E. coli: 5 mil Drosophila melanogaster: 140 mil Homo sapiens: 3.2 bil Paris japonica: 150 bil
39
Why does genome size not always correlate with the number of genes?
Though there exists a general correlation, there are many exceptions This is due to some parts of chromosomes not coding for polypeptides, especially in eukaryotes
40
Define diploid, haploid, gamete, sperm, egg, and zygote.
Diploid: containing two complete sets of chromosomes Haploid: containing only one set of chromosomes Gamete: a male or female reproductive cell capable of fusing with a gamete of the opposite sex to create a zygote For males, gametes are sperms For females, gametes are ova (ovum singular) aka eggs Zygote: a fertilized egg cell that is the result of the union of two gametes of the opposite se, that is able to develop into an organism
41
Compare the diploid chromosome numbers of: Parascaris equorum (equine roundworm) Oryza sativa (rice plant) Homo sapiens (human) Pan troglodytes (chimpanzee) Canis familiaris (domestic dog)
Organism: diploid chromosome number Parascaris equorum (equine roundworm): 4 Oryza sativa (rice plant): 24 Homo sapiens (human): 46 Pan troglodytes (chimpanzee): 48 Canis familiaris (domestic dog): 78
42
Define a karyogram and karotype.
Karyotype: The arrangement of homologous chromosomes in an organism Karyogram: A photograph of a karyotype, ordered by decreasing lengths, taken during metaphase of mitosis Homologous chromosomes are aligned by length, location of centromere and by bands of colour differences produced with dyes
43
Define nondisjunction, and the role of karyotyping in regards to it.
Nondisjunction is when sister chromatids fail to split during meiosis, resulting in a zygote having an extra or missing chromosome, conditions called trisomy and monosomy respectively Karyotyping, the act of taking a karyogram, allows doctors to identify chromosomal abnormalities, such as trisomy and monosomy
44
Describe how Down syndrome occurs, and why other trisomy disorders are not as well-known.
Down syndrome occurs when chromosome 21 of the human body has 3 copies; thus, it is also known as trisomy 21 Occurrences of nondisjunction in the majority of chromosomes are fatal and result in infertility, which explains why they are not as well known Down syndrome allows its gamete to develop, and its harms are comparatively less impactful
45
Describe a disadvantage of karyotyping (what it cannot detect), and provide an example of such.
Karyotyping cannot detect differences at the gene-level, only large-scale chromosomal differences such as trisomy and monosomy For example, it cannot detect base substitution mutations such as sickle cell anemia
46
Describe how Cairn measured the length of E. coli's DNA.
He used autoradiography, a technique that uses X-ray film to visualize the 2D distribution of a radioactively labelled structure The produced image is called a autoradiograph The process: Thymidine was produced with radioactive hydrogen isotope H-3 E. coli was grown in the presence of this The cells were lysed (burst open), spilling out its DNA onto slides The slides were covered with photographic emulsion and stored in the dark for two months Over the course of this period, high-energy electrons emitted by the radioactive decay of the H-3 isotope within the DNA caused the appearance of dark spots on the photographic emulsion sheet The pattern of dark spots showed the appearance of DNA, which he then measured to be 1 mm, about 1000 times longer than the typical E. coli cell
47
Compare and contrast asexual and sexual reproduction (briefly).
Asexual reproduction: there is only one parent, and it produces a clone (genetically identical organism) through binary fission Sexual reproduction: combines genetic information of two parents through meiosis; combines two opposite sex gametes to form a zygote
48
List all phases of meiosis.
MEIOSIS I: Prophase I Metaphase I Anaphase I Telophase I MEIOSIS II: Prophase II Metaphase II Anaphase II Telophase II
49
Fill in the blanks: meiosis consists of ___ ________ nucleus splitting into ____ _______ nuclei.
Meiosis consists of one diploid nucleus splitting into four haploid nuclei. Note that mitosis produces cells, but meiosis produces nuclei!
50
Describe meiosis, and name the phases.
Meiosis I: Prophase I: Nucleolus and nuclear membrane disintegrate Chromosomes supercoil and are thus visible Homologous chromosomes are duplicated, and each forms two sister chromatids All four total sister chromatids collectively are called tetrads or bivalents Non-sister chromatids inside the same tetrad may cross over at points as chiasmata and exchange equivalent segments of DNA Centrioles, if present, migrate to opposite poles, and spindle fibres form Metaphase I: Homologous pairs move together along the metaphase plate or equator Maternal and paternal homologues show random orientation in regards to facing the poles The spindle fibres connect each centromere to a single pole In metaphase I, there is no splitting or pulling apart chromosomes Anaphase I: Spindle fibres shorten and pull homologues away from their respective partner towards opposite poles Telophase I: The chromatids uncoil partially and a nuclear membrane reforms around each new nucleus Meiosis II occurs next: It is very similar to meiosis I, with a few exceptions: There is no crossing over in prophase II, as the homologous chromosomes were separated Metaphase II does not feature random orientation Anaphase II involves spindle fibres separating - pulling apart - sister chromatids, similar to mitosis's anaphase Sister chromatids, like in mitosis, become daughter chromosomes after pulled apart Note that the final products, four haploid daughter cells, are genetically distinct, unlike in mitosis, which are genetically identical
51
Describe the process of crossing over, and when it occurs.
Crossing over occurs in prophase I of meiosis When homologous chromosomes in a tetrad line up next to each other (an event known as synapsis), crossing over can take place Homologous pairs of sister chromatids exchange genes at chiasmata (single: chiasma), which creates new combinations of alleles E.g. two homologous chromosomes with genes AB and ab could crossover to become Ab and aB Crossing over contributes to genetic variation, as it introduces new, usually unique alleles
52
Describe the process of random orientation/assortment, and when it occurs.
When pairs of homologous chromosomes line up at the equator of a cell during metaphase I, both the maternal and paternal copy have an equal chance of facing each pole, allowing random assortment as the other stages of meiosis carry through This contributes to genetic variation
53
State the correlation between the age of the mother during pregnancy and the amount of chromosomal abnormalities.
Positive correlation; as mother's age increases, the amount of chromosomal abnormalities tends to increase as well There is also a similar correlation between the father's age and nondisjunction, but less compelling, as research suggests that, out of the cases of Down syndrome through nondisjunction, 90% comes from the mother, and 10% from the father
54
Define fetal karyotyping and state the two methods of doing so.
Fetal karyotyping: checking the karyotype before someone is born, or karyotyping a fetus Methods: Aminiocentesis Chorionic villus sampling (CVS)
55
Describe the process of amniocentesis, as well as its risks and the time period it is performed.
Performed between weeks 14 to 20 of a pregnancy Ultrasound imagery is used to guide a syringe needle through the mother's abdomen and uterine wall, without piercing the fetus The needle extracts a minute amount of amniotic fluid This fluid contains fetal cells, which are cultured and karyotyped Risks: - Leaking amniotic fluid - Miscarriage - Needle injury to fetus - Rh sensitization - Infection/infection transmission
56
Describe the process of chorionic villus sampling (CVS), as well as its risks and the time period it is performed.
Earlier in pregnancies (during weeks 10-13) there is not enough amniotic fluid to perform amniocentesis, so CVS is used Ultrasound imagery is used to guide a medical professional during sampling A suctioning tool (catheter or syringe) is inserted through the vagina or abdomen to reach the fetal cells in the chorion - The chorion is the membrane that surrounds the fetus and develops into part of the placenta The fetal cells are sampled, cultured and karyotyped Risks: - Miscarriage - Rh sensitization - Infection Poses a higher risk of failure than amniocentesis
57
State Mendel's three laws.
The Law of Segregation: the inheritance of each characteristic of an individual is a randomly selected combination of their parents' alleles The Law of Independent Assortment: the allele of one trait does not affect the inherited allele of any other trait Exception: genes whose loci are close together, called linked genes The Law of Dominance: in an organism with two different alleles (heterozygous), only one allele will determine the trait: the dominant one The unexpressed is called recessive Exceptions: codominance, incomplete dominance
58
Define homozygous and heterozygous, as well as dominant, recessive and codominant alleles.
Heterozygous: the alleles an individual has are different (e.g. Aa) Homozygous: the alleles an individual has are the same (e.g. AA, aa) Dominant allele: the allele that determines the organism's phenotype, denoted with a capital letter (e.g. A, b)) Recessive allele: the allele that is overshadowed by the dominant allele and is only expressed when an organism is homozygous with a recessive allele, denoted with a lowercase letter (e.g. a, b) Codominant alleles: alleles that will not suppress nor be suppressed by one another, and will instead both be expressed, denoted with a capital letter that indicates the trait followed by a capital superscript that indicates the allele (e.g. C^W, C^R)
59
Define incomplete dominance and codominance.
Incomplete dominance: when two alleles have their traits "blended" to produce an intermediate phenotype E.g. if C^W = white petals, C^R = red petals, then the genotype C^W C^R = pink petals Codominance: when two alleles are codominant, if an organism is heterozygous, both will be equally expressed E.g. if C^W = white petals, C^R = red petals, then the genotype C^W C^R = red-and-white spotted petals
60
Name the four main blood groups (not including positive/negative)
A, AB, B, O
61
Name the three alleles that determine the blood group of an individual, as well as the relation between the alleles (dominant, recessive, etc.) and the required genotypes for each group
Alleles: I^A, I^B, and i I^A and I^B are codominant with respect to each other, but dominant with respect to i Genotype: group I^A I^A or I^A i: group A I^A I^B: group AB I^B I^B or I^B i: group B ii: group O
62
State the blood types that each blood type can be donated (excluding positive/negative), and why this is the case.
Excluding positive and negative... Type A can receive type A or O Type B can receive type B or O Type AB can receive type AB, A, B or O Type O can only receive type O This is because of antigens and antibodies: Antigens are molecules in blood that serve as identifiers for the body If the body detects a foreign antigen in the blood, it sends antibodies to attack it Antigens have specific markers that depend on the blood type they are in, to ensure there isn't any self-sabotage For example, type A blood has antigens with A markers, therefore they have antibodies that attack any antigen except A Type AB has both A and B markers on their antigen, and type O does not have any markers The lack of markers on type O antigens gives it two notable characteristics: - It will never be attacked by any antibody, thereby allowing type O blood to be the universal donor - However, it will contain antibodies that attack both A and B markers, thereby disallowing type A, B or AB blood to be donated to it In contrast, the possession of both markers for type AB blood allows it to receive any type of blood (lack of anti-A and anti-B antibodies) but its blood will always be attacked when donated to an individual that is not type AB blood (markers will get attacked by both anti-A and anti-B antibodies)
63
State the patterns of genetic diseases.
Autosomal recessive Autosomal dominant X-linked dominant X-linked recessive Y-linked
64
Provide an example and description of an autosomal recessive and an autosomal dominant disease.
Autosomal recessive: cystic fibrosis Occurs due to a mutation in the CFTR gene on chromosome 7, which codes for a chloride channel in mucous membranes The altered mucus builds up in the lungs, causing infections and damage to lung tissue, and the liver and pancreas, making it more difficult to digest food Autosomal dominant: Huntington's disease Neurodegenerative disorder that starts to affect people between 30-50 Occurs due to a mutation in the HTT gene on chromosome 4 Symptoms include loss of muscle coordination, cognitive decline and psychiatric problems
65
Provide two examples and descriptions of an X-linked dominant sex-linked genetic disease.
Red-green colourblindness (aka protanopia) Self-explanatory Hemophilia A protein needed for blood clotting, usually factor VIII, is not made Small injuries may result in major blood loss
66
Outline the conventions of a pedigree chart.
Females are circles Males are squares A shaded shape means the individual is affected by the disease under inspection Parents and children are connected with a T shape Sometimes, but not often, half-shaded shapes indicates a carrier (when dominant allele suppresses effect of recessive disease) Roman numerals identify generations, and Arabic numerals identify individuals within a generation Exact genotypes are not known, but phenotypes are (if they have the disease or not)
67
Describe mutagens, and how they affect alleles.
A mutagen is any agent that causes/increases the frequency of mutations by triggering changes in the genetic material of an organism Includes chemicals and high-level radiation Could potentially form new, harmful alleles, and increase chances of cancer (in which case the mutagens are also called carcinogens) Most mutations made by mutagens will not be passed to offspring, as they were made to non-sexual cells They will only be passed on if present in the DNA of the cells that produce gametes
68
Describe radiation and its effect on genes. Provide two prominent examples of radiation exposure.
High energy radiation, also known as ionizing radiation, can break bonds between atoms including DNA, which causes mutations - E.g. UV light, X-rays, and alpha, beta and gamma radiation from the decay of radioactive materials August 6, 1945, an atomic bomb devastated the city of Hiroshima, Japan - Released a large amount of radiation, causing many deaths and cases of Acute Radiation Syndrome (ARS) 1986, the Chernobyl nuclear power station in Ukraine accidentally melted down, releasing a significant amount of radiation, much more than in Hiroshima The radioactive material is still present to date It resulted in a clear increase of thyroid cancer in children
69
Discuss why the observed outcomes of a genetic cross may not conform to the predicted outcomes, outside of the context of linked genes.
Probability The smaller the sample size, the more randomness affects results Larger sample sizes tend to conform to predicted outcomes more
70
Describe continuous and discontinuous variation.
Continuous variation: when there can be infinitely many possible phenotypes produced by genes - Think continuous data, no concrete numbers - Skin colour, height, etc. Discontinuous variation: when there are a finite amount of possible phenotypes produced - Think discrete data, concrete numbers - Blood type, earlobe attachment
71
Define monogenic and polygenic, and state the assumptions of the polygenic model.
Monogenic: when a trait is determined by only one gene loci Tend to exhibit discontinuous variation Polygenic: when a trait is determined by more than one gene loci Tend to exhibit continuous variation Assumptions: Each contributing gene has a small, relatively equal and additive effect The genes behave as if they are codominant There is no linkage involved The value of the trait depends solely upon genetics; environmental influences are ignored
72
Define genetic linkage and recombinant or variant gametes.
Genetic linkage: the tendency of certain genes to be inherited together Genetic loci that are on the same chromosome are physically close and tend to stay together during meiosis, thus making them genetically linked Denoted with vertical pairs separated by a double line When crossing over occurs, two linked genes may swap places (e.g. AB // ab --> Ab // aB) These alternate alleles can create recombinant or variant gametes These occur at a smaller rate compared to normal gametes, due to their dependency of crossing over
73
Describe the process of DNA sequencing.
By using a technique called the Dideoxy Chain Termination Method, scientists take advantage of the fact that adding dideoxy nucleotides to a DNA strand stops DNA synthesis Dye is added to four dideoxynucleotides (ddNTP's), which are added to the DNA sequence such that, when the DNA synthesis stops, the final base sequence is recognized by the dye shown Scientists do this repeatedly by using PCR (mass DNA cloning) and stop synthesis at every position to conclude the pattern of bases in a segment of DNA