BIOL2030 > Module 2 > Flashcards

Module 2 Flashcards

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1
Q

Who was Gregor Mendel?

A

An Augustinian monk interested in plant breeding.
- He was interested because the mechanisms of heredity were unknown at the time.
-

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2
Q

What was the theory of blending inheritance?

A

This was the idea that traits can blend in each generation and potentially blend away in some generations.
- This is extremely wrong.

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3
Q

How did Mendel do his work?

A

Mendel discovered heredity using mathematics, taught to him by Doppler, who showed him to quantify his findings.
- This is how his method different from other geneticists.
- He conducted experiments for 10 years, with large scale projects and extremely meticulous experiments. He conducted these with many offspring.

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4
Q

What ratios did Mendel look at?

A

Mendel looked at ratios of traits found in the offspring, addressing his results mathematically.

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5
Q

What was his magic ratio?

A

3:1 - phenotypic ratio of a heterozygous cross.
- found due to using a large sample size.

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6
Q

What are characters of Mendel’s model organism - pea plant?

A
  • 1 generation = 1 growth season
  • produce many offspring (large samples)
  • many varieties to choose from and study experimentally.
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7
Q

So, what were Mendel’s findings?

A
  • published this in 1865 and rediscovered in 1900.
  • traits do NOT blend
  • distinguished between genotype and phenotype
  • traits endure, and don’t blend.
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8
Q

What are Mendel’s 4 postulates?

A
  1. Inheritance is by factors or particles (didn’t know DNA/chromosomes)
  2. particles are present in pairs in breeding adults
  3. particles can have alternate (dominant/recessive) forms
  4. paired particles segregate independently during the formation of gametes; each contains only one particle (produced by meiosis)
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9
Q

What is the gene?

A
  1. a unit of inheritance (mendelian)
  2. a location on a chromosome (a gene’s locus)
  3. a sequence of base pairs
  4. a transcriptional unit (transcribed to make a protein)
  5. a determinant of an organism trait
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10
Q

Do all genes encode proteins?

A

NO! It is a common mistake to think that all genes encode proteins.
- Ex. Someone says that a chromosome has 2000 genes on it and what they really are referring to is 2000 protein encoding genes, but there are definitely more than that in total.

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11
Q

What are the three types of genes?

A
  1. protein coding
  2. RNA encoding
  3. regulatory signal
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12
Q

What are protein coding genes?

A

This is the standard way of thinking

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13
Q

What are RNA encoding genes?

A

encode RNA that does NOT get translated into a protein but does have a specific function.
Ex. tRNA and rRNA

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14
Q

What are Regulatory signal genes?

A

Their purpose is to provide information about timing or extend at which a particular piece of info gets expressed.
- This is genetic information related to and determines an organismal trait.

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15
Q

What is a genotype?

A

The complete genetic makeup of an individual organism.
- Also used to reference one gene or a set of several genes
- Refers only to the information content of nucleic acid

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16
Q

How are geneticists “pluralists” about genes?

A

They do not argue about which definition is best or most correct. They use different definitions thats most appropriate for the context that they are working in.

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17
Q

Example of SBE1 gene and Starch binding enzyme 1?

A

SBE1 is the DNA that encodes information on how to make starch binding enzymes 1. If functional it will play a role in starch biosynthesis and you will get a round seed phenotype.
- dysfunctional SBE1 enzyme produces a wrinkled cell phenotype due to a lack of starch biosynthesis and the buildup of sugars during seed development causes osmotic pressure.

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18
Q

What is actually passed on for SBE1?

A

SBE1 is what is actually passed on whereas the phenotype is not explicitly passed on.

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19
Q

What is a phenotype?

A

Phenotype is a measurable trait of an organism that is controlled by one or more genes but can be influenced by environmental effects.
- They are NOT inherited
- Ex. Seed shape different (wrinkled vs smooth) in pea plants.

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20
Q

What is meant by the idea that all living organisms use the same genetic system?

A
  • all hereditary information is encoded in nucleic acid
  • nucleic acids are a polymer made of nucleotide monomers
  • DNA is very nearly the universal genetic material
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21
Q

What are the two types of nucleic acids?

A

DNA and RNA. Monomers have the same basic structure: pentose sugar, which has a nitrogenous base and a phosphate group attached to them.
- Difference is on the 2’ carbon of the pentose sugar, in DNA we have H whereas in RNA we a have an OH.

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22
Q

Why is it relevant that we all have the same genetic system?

A

Because we all have genetic systems in common (DNA and RNA), principles of genetic transmission, quantitative genetics and population genetics that we learn all apply to ALL organisms.
- Therefore, genetics is a unifying principle in biology.

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23
Q

What organisms use RNA vs DNA?

A

RNA: some viruses
DNA: other viruses and all other life

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24
Q

What are the different nitrogenous bases?

A

There are 4 variants of the monomer (nucleotide) which differs according to the chemical structure of the nitrogenous base
- Chemical differences among the nitrogenous bases aren’t shown, but they are named for the nitrogenous base.

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25
What are alleles?
Genes combine alternate states, called alleles, in diploid individuals.
26
What is a dominant allele?
An allele whose trait is expressed in heterozygous individuals
27
What is a recessive allele?
An allele whose trait is NOT expressed in heterozygous individuals.
28
Example of allele R and r?
Allele R = functional protein made Allele r = defective protein made
29
Where are alleles encoded?
Alleles are encoded at their locus, named for the dominant phenotype. We then have two allelic variants.
30
Genotype examples with condition and phenotype results?
RR - homozygous - round Rr - heterozygous - round rr - homozygous - wrinkled
31
Where is genetic information encoded?
Genetic information is encoded by genes on chromosomes, and that information is transmitted ton the next generation via haploid gametes.
32
What is the principle of segregation?
This consists of allelic variation at a locus, separating alleles during gamete formation.
33
What is the principle of independent assortment?
This consists of allelic variation across loci, differential sorting during metaphase (maternal and paternal chromosomes line up independently of one another) - 2 genes that do NOT affect one another when they are on different chromosomes.
34
What is the principle of segregation?
An individual organism possesses two alleles for any particular trait, and these two alleles segregate (separate) such that each is transferred to its own gamete. - The transfer of alleles to gametes occurs with equal probability.
35
What do diploid organisms make?
Diploid organisms make haploid gametes, which become diploid through fertilization again.
36
What is allelic variation caused by?
Allelic variation is caused by segregating or separating chromosomes into each haploid gamete.
37
What is the probability of getting one allele over the other?
In heterozygotes, the probability of getting a particular allele is 1/2.
38
When do pairs of homologous chromosomes line up?
Pairs of homologous chromosomes line up in metaphase I.
39
Where does the principle of segregation refer to?
The principal of segregation refers to the process that affects allelic variation AT A SINGLE LOCUS (a single gene).
40
What is a monohybrid cross?
Monohybrid cross: a cross between parents that differ by a single trait.
41
What is the result of the F2 generation with a P generation that was true breeding?
results: * trait is NOT blend! * inheritance is “particulate” (i.e., there is a “gene” involved) * this trait “skipped” a generation (so, was not true-breeding in THIS cross) * classic 3:1 ratio
42
Genotypic and phenotypic ratios of an F2 cross for a monohybrid cross?
Genotypic: 1:2:1 Phenotypic: 3:1
43
What is probability?
No. of times a particular event is expected to occur out of the total number of possible outcomes
44
What is the sum (OR) rule?
The sum rule: * If disjoint events, then add probabilities * P(A or B) = P(A) + P(B) Ex: (Given 1 die) Prob of rolling a “1” OR “6” = 1/6 + 1/6 = 1/3
45
What is the product (AND) rule?
The product rule: * If joint events, then multiply probabilities * P(A and B) = P(A)*P(B) Ex: (Given 2 dice) Prob of rolling “1” AND “6” = 1/6 X 1/6 = 1/36
46
What is a dihybrid cross?
A dihybrid cross is in the case of a cross involving two traits
47
What rule do we apply in a dihybrid cross?
In the case of a cross involving two traits (dihybrid cross) we apply…. - The principle of independent assortment: alleles at different loci (on different chromosomes) segregate independently of each other.
48
Definition of a dihybrid cross?
Dihybrid cross: a cross between parents that differ by two traits. - Result is 4 different types of gamete types.
49
What does the principle of independent assortment tell us about behaviour?
The principle of independent assortment tells us that genes will behave differently from one another.
50
What is the generic form of a test cross?
homozygous recessive crossed with an unknown genotype.
51
What is a wild-type allele?
The allele most often found in natural populations. Often symbolized by one or more letters and a plus sign (+).
52
What is an allelic series?
The set of >2 alleles that occur within a given natural population. - A1, A2, A3, A4
53
What is conventional notation?
"A" locus with 2 alleles, AA, Aa, aa
54
What is allelic series notation?
"A" locus with >2 alleles. A1A1, A1,A2, A1,A3 etc
55
What is drosophila notation?
"ebony" locus denoted by "e" "wild type" allele = + "mutant" allele = - e+e+ e+e- etc.
56
What is an example of of locus specific notation?
human ABO group: 1 locus, 3 alleles (IA, IB, & i)
57
Different blood types?
Blood type O: i i Blood type A: IA IA or IA Ii Blood type B: IB IB or I BIi Blood type AB: IA IB - Difference is due to sugars on antigens on the blood.
58
What are characteristics of blood type alleles?
* three main alleles at a single locus (other rare variants do exist) * locus encodes glycosyltransferase enzyme * i allele is recessive to IA and IB alleles (i encodes non-functional protein) * i form does not modify the basic blood antigen structure * IA and IB alleles produce different variants of basic blood antigen structure
59
What is complete dominance?
The phenotype of the heterozygote is the same as the phenotype of one of the homozygotes. At the phenotypic level: RR = Rr ≠ rr
60
What is the biochemical basis of dominance?
Typically, in a biochemical pathway, half the amount of “normal” protein is produced by the heterozygote compared to the dominant homozygote. When half the amount of the “normal” protein is sufficient to obtain a given phenotype, the heterozygote is deemed haplosufficient.
61
What is haplosufficient?
This is when one allele is enough for the phenotype
62
What is incomplete dominance?
The phenotype of the heterozygote is intermediate between phenotypes of the two homozygotes. The heterozygote phenotype may fall at any point within the range of the homozygotes. At the phenotypic level: A1A1 > A1A2 > A2A2
63
Plumage colour in chickens example?
Black > Bluish-grey > White CBCB CBCW CWCW Two doses of CB are needed to give black; In heterozygotes a single CB allele results in only enough product for an intermediate phenotype (bluish-grey) - The heterozygote is haploinsufficient
64
What is haploinsufficient?
This is where one allele is not sufficient to give full colour.
65
What is different about incomplete dominance genotype vs phenotype?
Incomplete dominance causes the genotypic ratio to be equal to the phenotypic ratio.
66
What is co-dominance?
The phenotype of the heterozygote simultaneously expresses the phenotype of both homozygotes. The phenotype of the heterozygote does NOT fall within the range of homozygous phenotypes. - Both alleles are seen equally in heterozygotes essentially.
67
Where can genetic interactions occur?
Genetic interactions can occur between alleles at the same locus and between different loci
68
What is dominance?
Dominance: an allele at one locus interferes with or prevents (hides) the expression of a gene at the same locus.
69
What is epistasis?
Epistasis: an allele at one locus interferes with or prevents (hides) the expression of a gene at a different locus.
70
What are novel phenotypes?
interactions between loci can produce novel phenotypes (i.e., they are NOT predictable from the single locus effects)
71
What produces modified Mendelian ratios?
Interactions between loci can produce modified Mendelian ratios
72
Example of dominance?
Dominance (here, pea plant example): 1. one allele “masks” affect of other allele at same locus 2. no interactions between alleles at different loci 3. each gene (locus) affects phenotype independently (9:3:3:1)
73
Example of epistasis?
Epistasis: 1. allele at one locus “masks” affect alleles at a different locus 2. interactions between alleles at different loci 3. this can alter Mendelian ratios
74
What does epistasis alter?
This pattern (and the 9 : 3 : 3 :1 ratio) is critical to epistasis: 1. Remember it! (we will be referring to it often) 2. this ratio will be modified by epistasis
75
Result of recessive epistasis?
Recessive epistasis results in an (9:3:4) ratio
76
Result of dominant epistasis?
Dominant epistasis results in an (12:3:1) ratio
77
What is the result of duplicate recessive epistasis?
Duplicate recessive epistasis results in a modified ratio of (9:7)
78
What is the result of duplicate dominant epistasis?
Duplicate dominant epistasis results in a modified ratio of (15:1)
79
Kinds of epistasis?
independent gene action: 9:3:3:1 kinds of epistasis … 1. recessive epistasis (9:3:4) 2. dominant epistasis (12:3:1) 3. duplicate dominant epistasis (15:1) 4. duplicate recessive epistasis (9:7)
80
What is complementation?
The expression of a wild type phenotype in an individual carrying two mutant alleles. This is an indication that the alleles are on different loci.
81
Example of yeast complementation?
Two mutant haploid red gametes are crossed, forming a diploid white yeast. This is the restored wild type!
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