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Flashcards in Genetics Deck (85):
1

Allele

Two genes that occupy the same position on homologous chromosomes and cover the same trait.

2

Deleterious, mutation or allele

A mutation that causes injury or harm

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Types of chromosomal mutation

-Large deletions due to unequal crossing over
-duplication
-inversion
-translocation

4

Frameshift mutation

A chromosome that comes from the deletion or insertion of a base into a DNA sequence. Results in the shifting of all the following bases after this mutation

5

Genetic Drift

A process which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next

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Population

A group of individuals of the same species that live in the same area and can produce fertile offspring

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Gene pool

All copies of every type of allele at all loci in every individual in a population

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Locus

A specific place along the length of a chromosome where a given gene is located

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Assumptions of Hardy-Weinberg law (7)

-Mutation isn’t occurring
-Natural selection isn’t occurring
-The population isn't infinitely large
-All members of the population breed
-All mating is totally random
-Everyone produces the same number of offspring
-There is no emigration or immigration

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Hardy-Weinberg equation

p + q = 1
p2 + 2pq + q2 = 1

11

Independent assortment

The lining up of chromosomes along the center of the cell in meiosis. This is one of the causes of genetic variation

12

Microsatellite

This is a short, repeated sequence of DNA that appears at a certain locus on a chromosome

13

Missense mutation

Change of one base in the DNA sequence resulting in a different amino acid that the codon codes for

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Nonsense mutation

Results in a premature stopping of a DNA sequence as a result of a mutation

15

Nonsynonymous mutation

Nucleotide mutation that alters the amino acid sequence of a protein

16

Orthogenesis

Also called straight-line evolution, theory that organisms have the tendency to to evolve in a definite direction.

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Particulate inheritance

The theory that traits are inherited as discrete units known as genes

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PCR

(Polymerase Chain Reaction) A technique for amplifying DNA 'in vitro' using specific primers, DNA polymerase and nucleotides

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Phenotype

The observable physical and physiological traits or an organism

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Genotype

The genetic makeup, or set of alleles of an organism

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Pleiotropy

When one gene influences two or more unrelated phenotypic traits. e.g. sickle cell anemia or a gene that affects growth rate will affect height and weight

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Polygenic trait

When one characteristic is controlled by two or more genes.
e.g. eye colour

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Polyploidy

When cells and organisms contain more than two paired set of chromosomes. (Triploid and Tetraploid etc)

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Quantitative trait

Measurable phenotype that depends on many genes and the environment. Examples include height, weight and blood pressure

25

Isozyme

An enzyme that differs in its amino acid sequence but catalyses the sam reaction

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Restriction fragment lenght polymorphism (RFLP)

is a difference in homologous DNA sequences that can be detected by the presence of fragments of different lengths after digestion of the DNA samples

27

Recombination

pieces of DNA are broken and recombined to produce new combinations of alleles

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Segregation of alleles

Alleles become separated and each one enters a single gamete

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Selection, balancing

Two alleles are maintained in a population because of natural selection. e.g heterozygote advantage- an individual with Aa has higher fitness than both AA and aa individuals

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Natural selection

A process in which certain individuals with certain traits tend to survive and reproduce at higher rates than those without those traits

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Selection, disruptive

The extreme traits are favored as opposed to the intermediate ones (M shaped curve)

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Selection, directional

An extreme phenotype is favoured over the others causing the allele frequency over time to shift in the direction of that phenotype

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Selection, stabilizing

The population stabilizies on a more mean trait value, more bell shaped curve

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Silent mutation

Base substitution that results in no change of the amino acid that is coded for due to DNA being degenerate

35

Simple tandem repeat

A short tandem repeat is a microsatellite, consisting of a unit of two to thirteen nucleotides repeated hundreds of times in a row on the DNA strand.

36

Single nucleotide polymorphism

A variation of a single nucleotide that occurs at a specific locus on the genome in a population

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Synonymous mutation

Change in the codon for an amino acid but not resulting in a change of the amino acid

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Threshold traits

Show discrete phenotypes but are controlled by many different loci

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Twin studies

Twin studies allow researchers to examine the overall role of genes in the development of a trait or disorder. Can use both identical and non identical twins

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What does diversity mean?

Variety of living species (organisms) in an ecosystem

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Species

A group of organisms that are capable of producing fertile offspring

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Sexual Dimorphism

where the male and female look different from one another

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Transformation

a change in genotype and phenotype due to assimilation of foreign DNA

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Euchromatin

DNA that is partially or fully uncoiled (loosely packed), is active in gene expression an stains lightly

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Chromatin

complex of DNA and protein, and is found in the nucleus of eukaryotic cells

46

Histones

Proteins that are responsible for the first level of DNA packing in chromatin

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What fibers is chromatin organised into?

- 10-nm fiber
- 30-nm fiber
- 300-nm fiber
- metaphase chromosome

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Heterochromatin

dense packing, regions of chromatin are highly condensed, difficult for cell to express genetic info

49

Genome

The complete genetic information contained in an individual - gene+ chromosome

50

How many different stages of transcription are there?

3 - Initiation, elongation and termination

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What happens in the first stage of transcription (Initiation)

- Proteins signal the initiation of RNA synthesis and transcription factors control the binding of RNA polymerase, where it attaches to promoter region on DNA
- TATA box- considered to be the core promoter sequence in eukaryotes, the binding site of general transcription factors or histones
o Core DNA sequence 5’-TATAAA-3’ or some form similar which is usually followed by three or more adenine bases
o The sequence of AT bases means that this TATA box makes it easier for the DNA to unwind as AT bases only form two hydrogen bonds compared to GC which makes three

52

What happens in the second stage of transcription (Elongation)

Building of mRNA from the 3’ end of the nucleotide polymer with the use of free nucleotides that are available in the nucleus of the cell
- As RNA polymerase moves along the DNA, it untwists the double helix, 10 to 20 bases at a time (40 nucleotides per second in eukaryotes)
- A gene can be transcribed by many RNA polymerases at the same time

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What happens in the final stage of transcription (Termination)

- Release of RNA polymerase and mRNA following transcription of the terminator region of the DNA. This is triggered by a release factor.
- The resulting stretch of DNA that is transcribed is called a transcription unit
The termination of transcription is different in bacteria and eukaryotes
Eukaryotes – The polymerase continues transcription after the pre-mRNA is cleaved from the growing RNA chain; the polymerase eventually falls off the DNA
Bacteria - The polymerase stops transcription at the end of the terminator

54

The central dogma

The concept that cells are governed by a cellular chain of command : DNA-> RNA -> Protein

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Translation

The initiation stage of translation brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits
• First, a small ribosomal subunit binds with mRNA and a special initiator tRNA • Then the small subunit moves along the mRNA until it reaches the start codon (AUG)
• Proteins called initiation factors bring in the large subunit that completes the translation initiation complex
- Termination occurs when a stop codon in the mRNA reaches the A site of the ribosome
- The A site will then accept a protein called a release factor
- The release factor causes an addition of a water molecule instead of an amino acid
- This reaction releases the polypeptide, and the translation assembly comes apart

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Homozygous

Having identical genes for a particular characteristic (AA/aa)

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Heterozygous

Having two different genes for a particular characteristic (Aa)

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Phenotype

The physical appearance of an organism (genotype and env)

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Genotype

The genetic makeup of an organism

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Mendel's three laws

1) Law of dominance
2) Law of segregation
3) Law of independent assortment (two different genes at two different loci

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Organic extraction of DNA

Lyse cells with SDS/PK/(DTT)
• Sodium dodecyle sulfate (SDS) – ionic
detergent breaks down cell membranes
(inhibits enzyme activity)
• Proteinase K – degrades proteins at 55C but
not susceptible to SDS. Dissolves histones
• Dithiothreitol (DTT) – additive for difficult lysis
conditions, breaks disulfide bonds in strong
proteins like keratin

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The three steps of PCR

Denaturation, Annealing, Extension

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First step of PCR

Denaturation
DNA heated to 94C which breaks hydrogen bonds

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Second step of PCR

Primer annealing (55C)
- Oligonucleotides serve as primers for the DNA polymerase
- Target a specific sequence of base pairs
- Require a primer for each end of the two strands that will defin the ends of the molecule synthesised

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Third step of PCR

Extension (72C)
- DNA polymerase extends the primers, adding nucleotides onto the primer in a sequential manner
- Commonly use Taq polymerase as heat tolerant

66

Gel electrophoresis

- Separates fragments according to size
- Molecules pushed by an electrical field through a gel that contains small pores

67

Restriction enzymes

Recognize specific nucleotide sequences and then cut both strands of the DNA molecules. Often recognize palindromic sequences.
Used in DNA cloning, DNA fingerprinting and to quantify genetic variation

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Polymorphic

the presence of more than one allele at a locus

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Heterozygosity

Measure of genetic variation that accounts for either the observed or expected proportion of individuals in a population that are heterozygotes

70

Allozymes

different allelic forms of a protein

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Isozymes

different proteins that do the same job, but are produced from different loci

72

Restriction site fragment length poylymorphism

RFLP for short
- Amplify a region by PCR
- Then cut (digest) with a restriction endonuclease

73

Microsatellites

Tandem repeats of short sequence of base pairs:
cgtcgtcgtcgtcgt
number of repeats at polymorphic locus ranges from 5-100
Used in forensics/population genetics/conservation

74

Hardy-Weinberg Law

p2 + 2pq + q2 = 1
After one generation of random mating
the genotype and allele frequencies will
remain at these frequencies in perpetuity
in the absence of other forces

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Some of the effects of genetic drift

-changes allele frequencies
-erodes genetic variation in populations
-is a process that particularly affects small populations

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Discrete Variability

Polymorphisms which can be scored by simple visual methods. Presence /absence of certain characteristics

77

Meristic characters

values of these characters are restricted to integers therefore they are countable. e.g. number of vertebrae, fingerprint ridges, clutch size

78

Threshold characters

Characters with discrete alternatives. Expression of alternatives is determined by a threshold in an underlying continuously distributed trait being exceeded.
-adult-onset diabetes
-heart disease

79

Quantitative traits are influenced by

Environmental factors and many genes

80

Threshold traits

Coronary heart disease is not a continuous trait
but it is associated with many factors
- weight, diet, cholesterol, smoking, family history

add up to liability
Above a threshold value will be liable to the
trait

81

Standard deviation

The spread of results about the mean

82

Heritability

The proportion of a populations phenotypic variation attributable to the genetic factors

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Broad-sense heritability

the contribution of genetic factors to the total phenotypic variance

84

Narrow-sense heritability

the contribution of additive genetic factors alone to the total phenotypic variance

85

Infanticide

The killing of young offspring by an older organism of the same species