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MBG 2040 > Lecture > Flashcards

Lecture Flashcards

1
Q

What is a gene?

A

A fundamental unit of heredity, helps determine characteristics.

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2
Q

What is an allele?

A

Alleles are multiple forms of a gene.

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3
Q

What is the basic function of DNA?

A

DNA carries genetic information.

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4
Q

Every allele has a specific ______ on a chromosome.

A

Every allele has a specific locus on a chromosome.

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5
Q

What is the principle of segregation?

A

Homologous chromosomes segregate in Metaphase 1.

Diploid becomes haploid.

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6
Q

Give a brief overview of every step of mitosis.

A

(lecture 1&2)

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7
Q

What is the principle of independent assortment?

A

Chromosomes separate independently of one another. This increases genetic variability.
(dihybrid cross give 9:3:3:1)

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8
Q

What is an assumption made when discussing pedigrees?

A

If the trait is rare and autosomal recessive, then individuals who marry/mate into the pedigree are homozygous for the normal allele unless there is evidence to the contrary.

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9
Q

What are some types of recessive mutations? What is their flaw?

A

Null/ Amorphic allele:

  • non functional protein produced
  • no protein produced

Hypomorphic allele:

  • poorly functioning protein produced
  • reduced amount of normally functioning protein produced
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10
Q

What are some types of dominant mutations? What is their flaw?

A

Hypermorphic mutations:

  • overproduction of normal protein
  • production of protein with increased activity levels

Neomorphic allele:

  • presence of altered protein with new function
  • altered protein interferes with wild type allele (called dominant negative allele”)
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11
Q

What is the difference between the multiplication rule and the addition rule?

A

Multiplication rule: this AND that

Addition rule: this OR that

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12
Q

What is incomplete dominance?

Give an example.

A

BB, Bb, bb are are phenotypically different. Where Bb is an intermediate between two extremes.

Ex. red, white and pink, flower

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13
Q

What is codominance?

Give an example.

A

BB, Bb, bb are are phenotypically different.
Bb exhibits phenotypes of both homozygotes.

ex. spotted cow

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14
Q

There can be a single nucleotide mutation at any part of a locus that can affect the gene in different ways. True or False?

A

True.

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15
Q

The frequency of a particular allele is usually the same from one population to another. True or False?

A

False. The frequency of a particular allele often varies from 1 population to another.

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16
Q

When it comes to blood type, Gene I encodes for _____ enzyme.

A

When it comes to blood type, Gene I encodes for transferase enzyme.

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17
Q

How do transferase enzymes differ? What are the symbols associated with these differences?

A

I^A –> encodes transferase which adds acetylgalactosamine
I^B–> encodes transferase which adds galactose
i–> encodes nonfunctional transferase
I^A I^B –> encodes transferase with acetylgalactosamine and galactose

Note*: AB alleles are codominant and 2 distinct proteins are made

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18
Q

When an enzyme/ protein is no longer being produced, is produced at lower levels, or is nonfunctional, its alleles are considered to be _______ alleles.

A

When an enzyme/ protein is no longer being produced, is produced at lower levels, or is nonfunctional, its alleles are considered to be loss of function alleles.

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19
Q

A loss of function allele is dominant over a wildtype allele. True or False?

A

False.

Not always. Wild type is dominant over recessive loss of function. Dominant loss of function is dominant over wild type.

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20
Q

What is haplosufficiency?

A

Haplosufficiency occurs when a wildtype allele is mixed with a loss of function allele.
Half as much protein is synthesized, yet this is often sufficient to achieve the wildtype phenotype.

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21
Q

The dominant allele is always considered to be the normal allele, and the recessive allele is considered a mutation. True or False?

A

False. The dominant allele is not always considered to be normal, sometimes the dominant allele is considered to be a mutation.

ex. Dominant alleles can be gain of function or loss of function mutations

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22
Q

What is a gain of function allele?

A

Gain of function allele –> mutant dominant allele which produces a protein that has an increased function
(This is often detrimental)
ex. Huntington’s disease

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23
Q

What is needed to cause a recessive lethal allele death?

A

Need both copies of the allele

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24
Q

Lethal genes can only be expressed in homozygotes. True or False?

A

False. Dominant lethal genes can be expressed in both the heterozygote and homozygote.
They can be dominant and recessive.

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25
Q

How are dominant lethal alleles passed down?

A

Lethal alleles can cause death after the age of reproduction, meaning those dominant genes have the ability to be passed down.

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26
Q

What is the result of a dominant-negative allele?

A

The dominant-negative allele is has a polypeptide that interferes with wildtype polypeptide. This causes a severe mutant phenotype.

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27
Q

What is penetrance?

A

Penetrance- The proportion of individuals having a particular genotype that express the expected phenotype.

aka. variation in the population

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28
Q

What is expressivity?

A

Expressivity- The degree to which a phenotype is expressed (mild to severe).

aka. variation in the individual

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29
Q

What are the types of penetrance?

A
  • Complete penetrance (100% expected phenotype)

- incomplete penetrance (<100% expected phenotype)

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30
Q

What are the types of expressivity?

A
  • Constant expressivity (100% expressed phenotype)

- Variable expressivity (range of phenotypes)

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31
Q

Briefly explain incomplete penetrance with variable expressivity.

A

Identical known genotype produce a broad range of phenotypes due to varying degrees of gene activation and expression.

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32
Q

What are some environmental factors that can affect phenotypic expression?

A
  1. Age
  2. Sex
  3. Temperature
  4. Chemicals
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33
Q

The range of phenotypes expressed by a single genotype under different environmental conditions is referred to as the _______.

A

The range of phenotypes expressed by a single genotype under different environmental conditions is referred to as the norm of reaction.

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34
Q

Environmental factors alone cannot produce phenotype that is the same as the phenotype of an individual with another genotype. True or False?

A

False. Environmental factors alone CAN produce phenotype that is the same as the phenotype of an individual with another genotype.

ex. himalayan allele in rabbits

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35
Q

What is a phenocopy?

A

A change in phenotype arising from environmental factors that mimic the effects of a mutation in a gene.

Ex. can phenotypically copy a disorder from a chemical

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36
Q

Can controlling environment influence appearance of mutant phenotype?

A

Yes.

ch5, slide 43

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37
Q

Different combinations of alleles from two or more genes can result in different phenotypes, because of interactions between their products at the cellular or biochemical level. True or False?

A

True. This is called genetic interactions.

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38
Q

When considering complete dominance at two gene pairs contributing to a single trait, what is a dilute gene?

A

The “original” allele.

ex. blue eyes (recessive)

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39
Q

Complementation will only occur if the mutations are on the same genes. True or False?

A

False. Complementation will only occur if the mutations are on different genes.

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40
Q

When does complementation occur?

A

Complementation occurs when two strains of an organism with different homozygous recessive mutations that produce the same phenotype, produce offspring of the wild-type phenotype when mated or crossed.

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41
Q

What is a heterogenenous trait?

A

A mutation in any one of a number of genes can give rise to the same phenotype.

ex. deafness can be caused by a number of different genes.

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42
Q

What is epistasis?

A

The masking of the expression of one gene by another. No new phenotypes are produced.

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43
Q

What is the difference between and epistatic gene and a hypostatic gene?

A

The “epistatic gene” –> does the masking.

The “hypostatic gene” –> is masked

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44
Q

What are the F2 ratios for the following monohybrid crosses:

Complete dominance, Incomplete dominance/ codominance, recessive lethal allele.

A

Complete dominance –> 3:1
Incomplete dominance/ codominance –> 1:2:1
Recessive lethal allele –> 2:1

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45
Q

What are the F2 ratios for the following dihybrid crosses:

Complete dominance, Recessive epistasis, Complementation, Dominant epistasis.

A

Complete dominance –> 9:3:3:1
Recessive epistasis –> 9:3:4
Complementation –> 9:7
Dominant epistasis –> 12:3:1

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46
Q

What is pleiotropy? Give an example.

A

A single gene can be responsible for a number of distinct and seemingly unrelated phenotypic effects.

ex. sickle cell anemia, cystic fibrosis

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47
Q

What are inbred lines?

Hint: plants

A

Self-fertilized plants that are homozygous for alleles that were present in the founding line.

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48
Q

Hybrid plants usually grow taller and faster than inbreds. True or False?

A

True.

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49
Q

What is heterosis/ hybrid vigor?

A

When two different inbred lines are crossed, the hybrids are heterozygous for many genes.

These plants are usually taller and grow faster –> vigor.

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50
Q

What is the Hardy Weinberg equation?

A

When it comes to proportion:
p^2 x 2pq x q^2 = 1

When it comes to frequency (if there are only two alleles):
p + q = 1

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51
Q

The Hardy Weinberg principle is correct in the absence of what influences? Give 2.

A
  1. Nonrandom mating
  2. Unequal survival
  3. Population subdivision
  4. Migration
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52
Q

What is dosage compensation?

A

A way of equalizing gene expression in the face of different gene dosage.

(inactivation of 1/2 X chromosomes in females).

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53
Q

What causes the non-homologous X and Y genes to pair up during meiosis?

A

The pseudoautosomal regions of X and Y chromosomes are homologous.

Top: primary
Bottom: secondary

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54
Q

An individual can have anuploidy for sex chromosomes and still display sex-determined characteristics. This is called ______.

A

An individual can have anuploidy for sex chromosomes and still display sex-determined characteristics. This is called viable anuploidies.

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55
Q

A Barr body will be present in the nucleus every time an individual has _________.

A

A Barr body will be present every time an individual has 2 X alleles.

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56
Q

What does it mean when people say females are functionally hemizygous for X-linked genes?

A

Approximately 50% cells express one allele, and 50% cells will express the other allele.

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57
Q

Give an example of a female genetic mosaic.

A

Females that are heterozygous for X-linked traits.

ex. Red-green colour blindness in one eye.

58
Q

Ants, Bees and Wasps have polyploidy males. True or False?

A

False. Ants, Bees and Wasps have monoploidy (N) males.

59
Q

Polyploidy is common in plants and animals. True or False?

A

False. Polyploidy is common in plants but is rare in the animal kingdom.
(Polyploidy animals are often sterile)

60
Q

What are autopolyploids?

A

Individuals where the chromosome sets are all identical.
All chromosomes are derived from the same species. (non-disjunction in meiosis 1)

Autopolypoids usually have:

  • Less seed production
  • More vegetative growth
61
Q

Many polyploids are sterile due to problems with _____ and ______ of homologous chromosomes in meiosis.

A

Many polyploids are sterile due to problems with pairing and separation of homologous chromosomes in meiosis.

62
Q

What are the possibilities of occurrence in Meiosis 1 of a 3N=33 banana?

A
  1. 11 trivalent (all stay together

2. 11 bivalent, 11 univalent (2 paired, leaving one out)

63
Q

What is an allopolyploid?

A

A popyploid as the result of a cross between two or more species.

64
Q

Allohexaploid and amphidiploid are the same thing. True or False?

A 
True.
Allohexaploid: 6N=42
(chromosomes of different species)
Amphidiploid: 3N=42
(how many diploids you have within; bivalents)
65
Q

When producing a polyploid hybrid through a inter species cross, what is the goal?

A

The goal is for hybrid to have only beneficial traits.

66
Q

Chromosome doubling which could potentially restore fertility is not well tolerated in animals. True or False?

A

True.

67
Q

What is aneuploidy?

A

A diploid genome which lacks a chromosome or has an extra chromosome.

Trisomy & monosomy

68
Q

What are potential causes for aneuploidy?

A

Meiosis 1 non-disjunction: 2 trisomies, 1 monosomies.

Meiosis 2 non-disjunction: 1 trisomy, 1 monosomy, 2 normal gametes

69
Q

What are some examples of viable trisomies in humans?

A

Trisomy 21 –> down syndrome
trisomy 13 –> pautau syndrome
trisomy 18 –> edwards syndrome

70
Q

What are some aneuploid conditions in human sex chromosomes?

A
  • X0 Turner Syndrome
  • XXY Klinefelter Syndrome
  • XXX Triple X Syndrome
  • XYY Double Y male
71
Q

What happens in prophase 1 that contributes to higher chances of auneuploidy in gametes of females as they age?

A

Female eggs are arrested in prophase 1. They start to ofind their homologous pairs and start crossing over (recombinantion).
Joining and disjoining losens homologous pairs and they don’t separate properly.

*If bivalent dissociates, nondisjunction of the homologues occurs.

72
Q

Deletion/ Deficiency is a _______ chromosome segment.

This is also called _______.

A

Deletion/ Deficiency is a missing chromosome segment.

This is also called hypoploidy.

73
Q

Duplication is an _____ chromosome segment.

This is also called _______.

A

Duplication is an extra chromosome segment.

This is also called hyperploidy.

74
Q

A chromosome can’t be rearranged internally, but it can become joined to another chromosome. True or False?

A

False. A chromosome may become rearranged internally, or it may become joined to another chromosome

75
Q

What are the types of chromosomal inversions? Give a brief description of each.

A

Pericentric inversion:
- includes centromere (swap above and below centromere)

Paracentric Inversion:

  • occurs below centromere
  • when alleles of homologous chromosomes don’t align properly, inversion loop is formed (prophase 1) to allow homologous sequence to align

*Bottom chromosome loops on its own to reinstate correct order

76
Q

Translocation occurs with homologous chromosomes. True or False?

A

False. Translocations occur when a segment from one chromosome is detached and reattached to a different (nonhomologous) chromosome.

77
Q

What is a reciproal translocation?

A

Translocation where pieces of two non-homologous chromosomes are exchanged without any net loss of genetic material.

*In prophase 1, homologous chromosomes form a crosslike configuration.

78
Q

How are compound chromosomes formed?

A

Compound chromosomes are formed by the fusion of homologous chromosomes, sister chromatids, or homologous chromosome segments.

-Formed by robertsonian translocations

79
Q

When two non-homologous chromosomes fuse at their centromeres it is called ______.

(*Hint: 2 acrocentric chromosomes = 1 metacentric chromosome & small fragment)

A

When two non-homologous chromosomes fuse at their centromeres it is called Robertsonian translocations.

80
Q

Why do some dihybrid crosses act as a simple complete dominance (24:8)?

A
  • The R and L genes are linked on the same chromosome (RL and rl alleles segregate as linked genes)
  • There is some infrequent exchange between the chromosomes that harbor RL and rl
  • This exchange is called recombination
81
Q

How do we calculate frequency of recombination?

A

Frequency = (#of recombinants / total) x 100%

82
Q

In F1 of a dihybrid cross, you will get 4 classes of equal frequencies if the genes are linked. True or False?

A

False. In F1 of a dihybrid cross, you will get 4 classes of equal frequencies if the genes are NOT linked.

*If genes are linked get 2 major and 2 minor classes of offspring.

83
Q

Homologous recombination occurs during ______ of meiosis.

A

Homologous recombination occurs during PROPHASE 1 of meiosis.

84
Q

Generally speaking, a tetrad is the same thing as a bivalent. True or False?

A

True.

85
Q

What is a chiasma?

A

Physical unction between the homologous chromatids.

It is the site where recombination occurs.

86
Q

The further apart genes are from one another on a chromosomes, the more likely they are to have recombinants. True or False?

A

True.

Genes far apart = more likely to cross independently –> increases likelihood of recombination.

87
Q

If you know the frequency of recombination in a specific gene pair how would you determine their distance from one another.

A

Frequency = ___ map units

88
Q

Frequency = map units begins to plateau around ____% because at _____ map units, genes start to independently assort even if they’re on the same gene.

A

Frequency = map units begins to plateau around 50% because at 50 map units, genes start to independently assort even if they’re on the same gene.

89
Q

Pedigree analysis provides estimates of recombination frequencies to map genes on human chromosomes. True or False?

A

True.

90
Q

What makes bacteria valuable research objects? Give 2-3 points.

A
  • Small size
  • Rapid reproduction
  • Selective media (e.g., antibiotics) that can easily identify the presence of an active allele
  • Simple structures and physiology
  • Genetic variability
91
Q

Bacteriophages produce clearances called _____ on plates with dense bacterial cultures within hours of infection.

A

Bacteriophages produce clearances called PLAQUES on plates with dense bacterial cultures within hours of infection.

92
Q

What are some differences between bacteriophage T4 and Lambda?

A

T4:

  • Contains around 170 000 base pairs and 150 characterized genes
  • fairly large and complex genome
  • Phage goes through lytic phase to infect other cells (provides for quick and simple genetic experiments)

Lambda:

  • Contains around 50 000 base pairs and 50 genes
  • May be in lytic or lysogenic phase
93
Q

All bacteriophages are considered to be _______.

A

All bacteriophages are considered to be RETROVIRUSES.

94
Q

Explain the process of how retroviruses work.

9 steps

A
  1. Virus attaches to host cell at receptors in membrane.
  2. Viral core enters the host cell.
  3. Viral RNA uses reverse transcriptase to make complementary DNA; viral RNA degrades.
  4. Reverse transcriptase synthesizes 2nd DNA strand.
  5. Viral DNA enters nucleus & is integrated into the host chromosome, forming a provirus.
  6. On activation, proviral DNA is transcribed into viral RNA –> is exported to the cytoplasm.
  7. In cytoplasm, viral RNA is translated to proteins.
  8. Viral RNA, proteins, new capsids, & envelopes are assembled.
  9. Assembled virus buds from the cell membrane.
95
Q

What will cause a virus to go into the dormant phase?

A
  • Bacteria doesn’t have enough nutrients
  • Bacterial colony is drying for some reason.

*Virus will wait for host population to be healthy again.

96
Q

When phage DNA integrates into the bacterial chromosome, what does it become?

(Hint: lysogenic cycle)

A

When phage DNA integrates into the bacterial chromosome, it becomes a prophage.

97
Q

What are plasmids? How do they replicate?

A

Plasmids are additional genetic material (small circular DNA) that can replicate independently of the chromosome.

98
Q

What are episomes? How do they replicate?

A

Episomes are harge circular DNA that can integrate into the bacterial chromosome for replication or can remain separate.

99
Q

Gene transfer in bacteria is _______.

Hint: from donor cells to recipient cells

A

Gene transfer in bacteria is unidirectional.

100
Q

What are some ways gene mutations can be observed in bacteria. List 2-3.

A
  • Colony colour and morphology
  • Nutritional mutants (can not metabolise certain sugars, like lactose or galactose)
  • Prototrophs and auxotrophs (can not make certain amino acids, these need to be added to the growth medium)
  • Antibiotic resistance
101
Q

What conclusion can you make from a replica plating experiment?

A

A colony that grows ONLY on the supplemented medium has a mutation in a gene that encodes the synthesis of an essential nutrient.

102
Q

What are some methods of recombination occurring in bacteria?

(Hint: parasexual process)

A
  1. Transformation
    - transfer of a free ( out of cell) piece of DNA from 1 bacterium into another

Conjugation:
-direct transfer of DNA from one cell to another via establishment of a cytoplasmic bridge

Transduction:
- transfer of genes from one cell to another via bacteriophage

103
Q

which of the 3 parasexual processes are sensitive to DNase? Why?

A

Transformation. In this process the DNA is exposed to the environment outside of the cell.

104
Q

What does it mean if a bacterium is competent? What process does this refer to?

A

A competent bacterium can bind to exogenous DNA and transport it into the cell.
(It has a DNA receptor and translocation complex)
This is beneficial in transformation.

105
Q

The rate of cotransformation in bacteria is inversely proportional to _____.

A

The rate of cotransformation in bacteria is inversely proportional to gene distances.

(ch.9, slide 25)

106
Q

Conjugation is a kind of bacterial “sexual” reproduction, mediated by the _______.

A

Conjugation is a kind of bacterial “sexual” reproduction, mediated by the Fertility factor.

107
Q

The Fertility factor is a type of plasmid. True or False?

A

False. The F factor is a type of episome.

108
Q

Describe the process of mating & conjugation of fertility factors.
(4 steps)

A
  1. F pilli of F+ donor cell make contact with F recipient cell & pulls them together.
  2. Genes on f-factor direct the synthesis of conjugation bridge. 1 strand of DNA is cleaved at origin of f-factor replication.
  3. Rolling circle replication transfers 1 strand of f-factor into recipient cell. Replication of f-factor occurs in both cells (1 in each) during transfer.
  4. Transfer of f-factor is completed–> yields 2 F+ bacteria.
109
Q

What is an Hfr cell?

A

A cell whose F-factor is integrated into its bacterial chromosome.

*This cell chromosome will nick at the F-factor, and will conjugate to transfer specific genetic information.

110
Q

Genes located close to one another are more likely to be co-transducted. True or False?

A

True.

111
Q

What are some functions of genetic material?

A
  • Replicate
  • Control growth & development of organism
  • Allow organism to adapt to changes in the environment
112
Q

What was the Griffith experiment and what was its conclusion?

A

Virulent bacteria, non virulent bacteria, heat killed virulent bacteria, non-virulent + heat killed virulent bacteria.

Conclusion: A substance in the heat-killed virulent bacteria genetically transformed the non-virulent bacteria into live, virulent bacteria. (Bacteria can pick up environmental DNA).

113
Q

What was the Avery, MacLeod, McCarty experiment and what was its conclusion?

A

Virulent bacteria treated with protease, RNase, or DNase.

Conclusion: Since only DNase destroyed the transforming substance, the transforming substance must be DNA.

114
Q

What was the tabacco mosiac virus (TMV) experiment and what was its conclusion?

A

Take off protein from RNA, create hybrid virus (red rna with blue proteins).
Conclusion: The type of RNA in hybrid TMV determines the RNA and protein of the progeny viruses

115
Q

Nucleic acids are composed of ______.

A

Nucleic acids are composed of NUCLEOTIDES.

116
Q

What are nucleotides composed of?

A
  • Nitrogen-containing bases
  • Pentose sugar
  • Phosphate (phosphodiester bond)
117
Q

What are the nitrogen-containing bases?

A 
A = Adenine
T = Thymine
G = Guanine
C = Cytosine
U = Uracil
118
Q

What are the types of sugars in nucleotides?

A
  • Deoxyribose

- ribose

119
Q

What nitrogen bases are purines?

A

Adenine, Guanine

120
Q

What nitrogen bases are pyrimidines?

A

Cytosine, Thymine, Uracil

121
Q

Purines are bigger than pyrimidines. True or False?

A

True.

122
Q

Nucleotides are joined together by ______ bonds.

A

Nucleotides are joined together by phosphodiester bonds.

123
Q

What did Erwin Chargaff discover?

A

purines = pyrimidines

124
Q

What are some assumptions of the Watson- Crick model?

A

Assumptions:

  • DNA is a double helix
  • The two strands were anti-parallel
  • The sugars form a phosphate backbone
  • The bases are held together by H bond
125
Q

How many bonds are found between T and A? What kind of bonds are they?

A

2 H-bonds.

126
Q

How many bonds are found between C & G? What kind of bonds are they?

A

3 H-bonds.

127
Q

What are the distances of the minor and major groves of DNA?

A

Minor: 0.34nm
Major: 3.4 nm

128
Q

To coil a strand of DNA, you need to introduce a _______.

A

To coil a strand of DNA, you need to introduce a single nick.

129
Q

What is ligation?

Hint: DNA coiling

A

Ligation: strand needs to seal the nick created so that it is able to keep energy inside & the coil doesn’t unravel.

130
Q

What are the dimensions of an E. coli DNA strand and cell?

A

DNA: 1.5mm circle
Cell: 2microm x 1 microm

131
Q

How is bacterial chromosome formed?

3 stages + size

A

Circular unfolded: 350microm
40-50 loops: 30microm
Supercoiled & folded: 2microm

*Has one genome (monoploid)

132
Q

What are the types of proteins found in eukaryotic chromosomes?

A
  • 5 histones (Highly positively charged polypeptides)

- A divergent group of non-histone proteins

133
Q

What is Chromatin?

Hint: equation

A

Chromatin = DNA + Histones + Protein

134
Q

What does each nucleosome core consist of?

A

Nucleosome core consists of an octamer of histones (11nm).

Octamer: 2 of each H2a, H2b, H3, H4

135
Q

Nucleosome core has ___ nucleotide pairs of DNA wrapped as ___ turns around an octamer of histones.

(Hint: both answers are numbers)

A

Nucleosome core has 146 nucleotide pairs of DNA wrapped as 1.75 turns around an octamer of histones.

136
Q

How many nucleotide pairs does the linker of a nucleosome have? What is its size?

A

Has 8-113 nucleotide pairs. Is 2nm wide.

137
Q

The complete nucleosome contains histone ____.

A

The complete nucleosome contains histone H1.

138
Q

What is the size of chromatin fiber?

A

30nm.

139
Q

Chromatin fiber is also called _____.

A

Chromatin fiber is also called solenoid.

140
Q

In the 3rd level of packaging of a chromosome, the 30nm chromatin fiber is attached to the 300nm chromosome ________.

A

In the 3rd level of packaging of a chromosome, the 30nm chromatin fiber is attached to the 300nm chromosome scaffold.

MBG 2040 (1 decks)

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