Exam 1 Flashcards
1
Q
What are true breeding lines?
A
plants that always produce progeny (offspring) with the same traits when self fertilized
2
Q
What is a trait (variant)?
A
A version of a character. If the character is “height” then the trait would be “tall” or “short”
3
Q
What is a character?
A
A characteristic that can vary, such as height.
4
Q
What is an allele?
A
One of a pair of genes that appear at a particular location on a chromosome.
5
Q
What is the Law of Segregation?
A
During gamete formation, the alleles segregate RANDOMLY.
Half of the gametes receive one allele, and half receive the other.
6
Q
When does the Law of Segregationn occur during Meiosis?
A
During Anaphase II, the sister chromatids split to leave one allele in each gamete.
7
Q
What is a gene?
A
DNA sequence encoding for a protein or some other genetic product
8
Q
What is an allele?
A
An allele is like a trait; it is a version of a gene.
9
Q
What is the Law of Independent Assortment?
A
During gamete formation, the segregation of any pair of alleles (from gene A) is independent of the segregation of another pair of alleles (from gene B).
It is the random distribution of homologous chromosomes during Anaphas I of Meiosis.
10
Q
How do you calculate the chance of having multiple specific genese occuring?
A
1) Create a punnett square for each character (each gene)
2) Multiply the ratios of each punnett square for each character for the sought after phenotype.
11
Q
What are some characteristics of an autosomal recessive inheritance pattern?
A
1) Affected offspring from unaffected parents
2) Unaffected sons from affected mother (can’t be x-linked)
12
Q
What does a low Chi Square value indicate?
A
High probability that data is due to random chance; fail to reject the null hypothesis
13
Q
What does a high Chi Square value indicate?
A
Low probablity that data is due to random chance; reject the null hypothesis
14
Q
What is Dosage Compensation?
A
A mechanism which keeps levels of X chromosome EXPRESSION in balance with autosomal chromosome expression.
15
Q
Which chromosome promotes male development and which gene is responsible?
A
The Y chromosome carries the Sry Gene which is responsible for male development.
16
Q
What is X-chromosome inactivation?
A
In mammals, one X chromosome is turned off chosen at random. Occurs in females.
17
Q
What is a Barr Body?
A
Inactivated X chromosome; the number of Barr Bodies is the # of X chromosomes minus 1.
18
Q
What is the Lyon Hypothesis?
A
female mammals inactivate one of their x-chromosomes in each somatic cell.
19
Q
What is the X-Inactivation Center and Xist?
A
There is a region on the X chromosome known as the X-inactivation center (Xic). This contains the x-inactive specific transcript (Xist) gene. The Xist gene is active on the condensed chromosome in Barr Body.
20
Q
What arer the phases to X-chromosome inactivation?
A
a) Initiation: x-chromosome is selected for inactivation
b) Spreadinng: Xist is expressed on the chromosome. The Xist transcripts coat the chromosome. Proteins are then recruited to condense the chromosome.
c) Maintenance: the inactivated chromosome is maintained even through mitosis.
21
Q
What are sex-linked genes?
A
Genes specific to X or Y chromosome
22
Q
What are pseudoautosomal genes?
A
Found on both X and Y chromosomes; inheritcan pattern similar to autosomal genes.
23
Q
What is characteristic of an X-linked recessive inheritance pattern?
A
1) Disease is rare in females; may be carriers
2) Carrier mothers have around 50% affected SONS
24
Q
What are wild type alleles?
A
The alleles that are prevalent in a natural population; the “normal” alleles
25
What is genetic polymorphism?
The presence of more than one wild-type allele
26
What is typical of mutant alleles?
Generally cause some sort of threat to survival; generally not a good thing
27
What is a gain of function mutation?
Change in the gene of the encoded protein so that is gains a new or abnormal function
28
What is a Dominant Negative Mutation?
Change a protein such that the mutant protein acts antagonistically to the normal proteinn
29
What is haploinsufficiency?
Dominant mutant allele is a loss-of-function allele. Used to describe a heterozygote that exhibits abnormal or disease phenotype.
30
What is incomplete penetrance?
Refers to a situation in which an allele expected to cause a phenotype does not cause that phenotype.
40% penetrance means 40% of the population has the allele and the expected phenotype.
31
At what level does incomplete penetrance occur?
At the population level; it is a proportion of individuals that have a specific allele and the associated phenotype.
32
What is incomplete dominance?
Occurs when the phenotype of a heterozygote is intermediate between the corresponding homozygous individuals.
With **Complete** Dominance, at least 50% of the functional protein is enough to express the dominant phenotype. With **Incomplete** Dominance, this is not the case.
33
What is Overdominance?
Otherwise known heterozygote advantage.
Occurs when Heterozygotes have greater reproductive success. For example, individuals that carry both the dominant Hemogloobin gene and the recessive Sickle Cell gene are at an advantage. The recessive sickle cell gene helps combat malaria; the heterozygote does not express the sickle cell trait because it is recessive but instead benefits from it.
34
What is Codominance?
Phenomenon in which two alleles are both expressed in a heterozygous individual.
35
What is sex influenced inheritance?
An allele is dominant in one sex but recessive in the other.
Occurs only in HETEROZYGOTES
Genes are autosomal (not sex linked)
36
What is sex limited inheritance?
Refers to the inheritance of a trait expressed by only ONE of the sexes
Genes can be autosomal or sex linked
Results in sexual dimorphism: different sexes have different morphological features.
37
What is pleiotropy?
The expression of a SINGLE gene causes MULTIPLE phenotypic effects.
38
What is gene interaction?
Refers to how the allalic variants of two DIFFERENT genes affect a single trait. There are three types:
1) Epistasis
2) Complementation
3) Gene Redundancy
39
What is Epistasis?
the alleles of one gene mask the phenotypic effects of the alleles of a different gene.
40
What is complementation?
Two different parents that express the same or similar recessive phenotypes produce offspring with a wild type phenotype.
41
What is gene redundancy?
one gene can compensate for the loss of function of another gene. The gene doing the compensation is called a paralog; it is a similar copy of a gene that can replace the function of a defective gene.
42
What is extranuclear inheritance?
Inheritance patterns of traits NOT in nuclear genes.
Comes from organelle genomes (chloroplast and mitochondria, which both follow maternal inheritance).
DOES NOT follow Mendelian Inheritance.
43
What is Genomic Imprinting?
Gene expression depends on the parent it was inherited from. The silence allele is the "imprinted" allele.
Example: Maternally imprinted means that the allele from the mother is silenced and the one from the father is activated.
44
What is Maternal inheritance?
A form of extranuclear inheritance that occurs through the cytoplasm of the egg. An example is inheriting genomic material from organelles in the egg, such as from the mitochondria.
45
Where is genetic material found in Mitochondria?
In the nucleoid, of which there are multiple (usually). Each nucleoid has more than one copy of the mitochondrial chromosome.
46
What does the mitochondrial DNA encode for?
rRNA and tRNA which is used to synthesize polypeptides
47
What is paternal leakage?
When the sperm cell provides the mitochondrion in a species in which maternal inheritance is usually followed.
48
What is Epigenetic Inheritance?
A form of imprinting. A modification occurs to a nuclear gene or chromosome that alters gene expression.
NOT permanenet over the course of many generations
Modifications usually occur during oogenis, spermatogenesis, or early stages of embryogenesis.
49
What is monoallelic expression?
Only one of the two alleles of a given gene is transcriptionally expressed because the oother allele has been silenced due to imprinting.
50
When is imprinting established?
During gametogenesis
51
What are the 3 stages of imprinting?
1) Imprint established during gametogenesis
2) Maintenance of the imprint during embryogenesis and in adult somatic cells
3) Erasure and re-establishment of the imprint in the germ cells of the new adult
52
Is Genomic Imprinting permanent?
It is permanent in the adult somatic cells but may differ from generation to generation
Can involve a single gene, part of a chromosome, a whole chromosome or even all chromosomes from one parent
53
What is DNA Methylation?
Used to mark a gene or chromosome for imprinting.
Attaches a methyl group onto a cytosine base in DNA.
Methylation marks for SILENCING.
54
What is an Imprinting Control Region?
Used in DNA Methylation. The ICR is located near the imprinted gene and contains binding sites for one ore more proteins that regulate transcription of the imprinted gene.
55
What is the Maternal Effect?
Refers to an inheritance pattern for certain NUCLEAR genes. The genotype of the mother DIRECTLY determines the phenotype of the offspring.
The genotypes of the father and offspring themselves do not affect offspring phenotype.
56
What are Nurse Cells with respect to the Maternal Effect?
Provide ooctye with nutrients; produce both dominant and recessive gene products (which reflect the mother's phenotype) that. are then moved into the oocyte.
These gene products persist well into embryo development.
57
What does the accumulation of maternal gene prodcuts via Nurse Cells accomplish?
Allows for embyogenesis after fertilization to proceed very quickly.
58
What types of things do maternal effect genes affect?
Cell division, cleavage pattern, and body axis orientation.
59
What is genetic linkage?
2 genes on the same chromosome are inherited as a couple. There is no independent assortment possibl.
60
What is synteny with respect to genetic linkage?
Genes that co-localize together. This conserves the order of genes between species.
61
How does recombination factor into genetic linkage?
Crossing over between homologous chromosomes can occur, which is a physical exchange of genetic material between two homologous NON SISTER chromatids.
The farther away two linked loci are from each other, the more likely recombination cann occur between them thus separating them.
The closer they are together, the less likely they are to be separated via crossing over.
62
What are recombinant offspring?
Those offsprinng which are unique of the parental phenotypes. Usually unique in at least one allele from the parental genotype.
63
What is a metacentric chromosome structre?
Centromere is perfectly in the middle
64
What is a submetacentric chromosome structure?
The centromere is slightly off center
65
What is an acrocentric chromosome structure?
The centromere is close to one end. Produces noticeable short arms.
66
What is a telocentric chromosome structure?
The centromere is at one end.
67
What is a chromosomal deletion?
Portion of the chromosome is missing; can be the most damaging. It is most common at the ends of the chromosome.
68
What is a chromosomal duplication?
Repeated chromosome segment; can provide additional genes or functions.
69
What is a chromosomal paracentric inversion?
An inversion in the order of a segment of the chromosome. The inversion does not include the centromere.
70
What is a chromosomal pericentric inversion?
Inversion in the order of a segment of the chromosome that does include the centromere.
71
What is a chromosomal reciprocal translocation?
Two differrent chromosomes have exachanged pieces of genetic material with each other
72
What is a balanced chromosomal translocation?
Part of a chromosome breaks off and reattaches to the same chromosome but in a different location.
73
What is a non-reciprocal translocation?
Part of one chromosome breaks off and attaches to another chromosome
74
What are linkage groups?
Another term for chromosome types. The number of linkage groups is the number of unique chromosome types. Each autosome is 1, each unique sex chromosome is 1, and mitochondria contain another 1.
75
What is a single factor cross?
A cross between two organisms that share the same genotype (and the same characteristic); it is specific to 1 characteristic such as height.
An example would be breeding a tall pea plant with a tall pea plant; the parental line is true-breeding
76
What is a monohybrid cross?
A cross that focuses on one given characterstic but the parents differ in that characteristic.
For example, a tall pea plant is bred with a short pea plant.
77
When does crossing over occur?
During Prophase 1
78
What are recombinant cells?
Genotypically unique from the parent cells; they contain a novel combination of genetic material.
79
What are recombinant offspring?
Offspring with novel genotype from parents; carry chromosomes as a product of crossing over
80
What is genetic mapping?
Used to determine the linear order AND separation distance among linked genes on the same chromosome.
81
What is a locus?
Site where a gene is found on a chromosome.
82
How does genetic mapping work?
A test cross is required between a heterozygous individual (for two different genes) and a homozygous individual (for two different genes)
The map distance is the number of recombinant offspring divided by the number of total offspring. This value is then multiplied by 100.
One map unit is equivalent to 1% of frequency of recombination
83
Does the homozygote or the heterozygote undergo recombination?
Functionally, only the heterozygote undergoes recombination because it can produce multiple different gametes.
84
What is the maximum reliable map unit and why?
50 mu is the max because a test cross is expected to yield a max of 50% recombinant offspring
85
What are the steps for genetic mapping for three-factor crosses?
1) Coss two true-breeding strains that differ with regard to 3 genes (goal is to obtain F1 individuals that are all heterozygous for the 3 traits)
2) Testcross: mate F1 female heterozygotes to male homozygous recessive
3) Collect F2 generation data
See Page 49 for more information
86
What is mitotic recombination?
Crossing over can occur during mitosis, which can result in mitotic mosaicism. If mitotic recombination does occur early in embryonic development, the somatic cells in which it occurs continue to divide. This causes a patch of tissue w/ unique charactertistics in the adult.
87
What is cytogenetics?
The microscopic study of chromosomes
88
What are duplications caused by?
Abnormal crossing over due to misaligned homologues; such mis-alignment is caused by repetitive sequences
Repetitive sequences are segments of DNA that have identical or similar sequences
89
What is non-allelic homologous recombination?
Crossing over occurs at homologous sites (like repetitive sequences) insread of at the same allelic site.
90
What are homologous genes?
2 or more genes are dervied from the same ancestral gene
91
What is copy number variation?
A type of structural variation in which a segment of DNA that is 1000 bP or more exhibits copy number differences (in genes) among members of the same species
92
What is a common cause of Copy Number Variation
Non-allelic homologous recombination can result in a duplication or deletion, thus altering the copy number of a gene
93
What is the position effect?
The place where a gene is placed can affect its expression. It usually plays a role in inversion.
94
What is an inversion heterozygote?
95
What does crossover in a paracentric inversion produce?
A chromosome that has 2 centromeres known as a dicentric chromosome.
96
What are the 2 centromeres in a dicentric chromosome connected by? What happens as these two centromeres separate?
A dicentric bridge. During anaphase, the 2 centromeres move to opposite poles and causes the dicentric bridge to break in a random location.
The end result is:
1 Normal Chromosome
1 Inverted Chromosome
2 Chromosomes w/ deletions (from the breakge of the dicentric chromosome)
97
What structure tends to prevent translocations?
Telomeres
98
How is translocation different than crossing over?
Crossing over occurs when Homologous chromosome exchange information during meiosis. Translocationoccurs when Nonhomologous chromosomes exhange information during meiosis
99
What governs the segregation of translocated chromosomes?
The centromeres; each gamete receives on centromere from chromosome A and one from B.
Remember, there are 4 centromeres between 2 pairs of homologous chromosomes. Thus, 4 gamte cells form.
100
What is alternate segregation?
Chromosomes diagonal to each other within the translocation cross sort into the same cell
Result: 2 normal gametes, 2 balanced chromosome gametes
101
What is adjacent 1 segregation?
Adjacent chromosomes (one with each type of centromere) segregate into the same cell
Result: 4 unbalanced chromosome gametes
102
What is adjacent 2 segregation?
Centromeres do not segregate properly, one daughter cell gets both chromosome A centromeres and the other gets both from chromosome B
Result: 4 abnormal gametes, all unbalanced
103
What is a euploid organism?
Chromosome number is an exact multiple of a chromosome SET
104
What is aneuploidy?
There is an extra copy, or loss of, one or multiple chromosomes within a set.
105
What is endopolyploidy?
Occurence of polyploid cells in organisms. Some cells have multiple sets of chromosomes that differ from the rest of the organism.
106
What is a bivalent?
One pair of homologous chromosomes in a tetrad.
107
What is a polytene chromosome?
Repeated rounds of chromosomal replication produces a bundle of chromosomes the lie together in parallel fashion.
108
How does endopolyploidy differ from a polytene chromosome?
In a polytene chromosome, the chromosomes remain attached to each other via a structure called a chromocenter.
109
What is nondisjunction?
Occurs when chromosomes do not segregate properly. Can be meiotic or mitotic.
110
What is meiotic nondisjunction?
Produces gametes with too many or too few chromosomes. Occurs during anaphase of meiosis 1 or 2
111
What is mitotic non-disjunction?
Occurs during embryonic development; may produce a patch of tissue in the organism with an altered chromosome number.
112
What is an alloploid organism?
Contains chromosome sets from multiple species
113
What is complete meiotic non-disjunction?
Chromosomes completely fail to separate which results in a diploid cell and a cell with 0 crhomosomes. All of the chromosomes migrate to one daughter cell.
The diploid cell can be fertilized; leads to triploidy
114
T or F: Meiotic non-disjunction can produce aneuploidy or polyploidy
True; gametes end up either missing one chromosome which upon fertilization would. result in monosomy or gaining an extra chromosome which upon fertilization would reulst in trisomy (both examples of aneuploidy).
Complete nondisjunction results in triploidy (euploidy)
115
What is mitotic nondisjunction?
Nondisjunction that occurs during mitosis. The end result is a patch of tissue w/ an altered chromosome number. This is called mosaicism.
116
How can mitotic nondisjunction occur?
1) Sister chromatids do not segregate properly; one daughter cell has 3 copies and the other has 1
2) During anaphase, sister chromatids do not seperate proerply. One of the chromatids isnt properly attached to the spindle and does not move to the pole. It is degraded. The end result is one daughter cell with 2 copies, and the other has 1.
117
What is genetic transfer in bacteria?
Process of a segment of DNA from one bacterial cell being transferred to another. Introduces bacterial genetic variation
118
What are the three types of bacterial genetic transfer?
1) Conjugation
2) Transduction
3) Transformation
119
What is conjugation?
Involves direct physical contact between two bacterial cells. One bacterial cell acts as a donor and transfers genetic material to a recipient cell.
120
What is transduction?
Virus infects a bacterium and then transfers bacterial genetic material from that cell to another
121
What is transformation?
A bacterial cell takes up DNA from the environment.
122
What is an auxotroph?
Bacterial strain that cannot synthesize a particular nutrient and needs that nutrient to be supplemented in a growth medium
123
What is a prototroph?
A bacterial strain that can synthesize a particular nutriend and does not need it to be supplemented via a growth mediu.
124
What are donor strains in conjugation?
Contain an F Factor (F stands for fertility). The donor donates genetic material.
125
What is an F Factor?
A small, circular segment of genetic material in addition to the main circular chromosome. It carries the genes required for conjugation; the Sex Pilus is nade by F+ strains.
126
What are Sex Pili (singular: pilus)
Made by F+ strains, act as attachment sites for conjugation. The gene encoding for. the pili structure is on the F Factor
The sex pilus extends from an F+ strain and searches for an F- strain (F- strain is the recipient)
127
What are plasmids?
Structures that exist independently of the chromosomal DNA; they are not necessary for survival but usually provide an advantage
128
What are Hfr Strains?
Have an F Factor inside the bacterial chromosome.
129
How are Hfr strains formed?
Formed by an F Factor aligning with a chromosomal region. Recombination allows the F Factor to integrate into the bacterial chromosome. Inegration can occur at various sites.
130
Explain how F prime factors form. What are F prime factors?
F prime factors form from the excision of the F factor from the bacterial chromosome. The excision is imprecise, which results in some F Factor genes remaining integrated while the rest can leave the chromosomal DNA.
F prime factors are simply F factors that carry a portion of the bacterial chromosome.
131
How does Hfr Conjugation occur?
Hfr strains can transfer a portion of the bacterial chromosome to a recipient (F-) cell. This occurs linearly meanning that if gene A comes before gene B on the Hfr strain, then gene A is transferred first.
132
Does Hfr Conjugation usually occur to completion?
No, only some of the Hfr strain is transferred. The longer the conjugation occurs, the longer the received DNA segment will be.
133
What is the origin of transfer?
A sequence of Base Pairs whose orientation promotes either CW or CCW transferrance of DNA (remember that bacterial DNA is circular). It lies in the Hfr strain.
134
How does the location of genes with respect to the origin of transfer relate to how they are transferred?
Genes closest to the origin of transfer get transferred first.
135
What is the lytic cycle?
The lytic cycle is one of the two cycles of viral reproduction, the other being the lysogenic cycle. The lytic cycle results in the destruction of the infected cell and its membrane
136
What is a transducing phage?
A phage that is assembled with a random piece of bacterial DNA; later binds to a living cell to inject is genetic material thus enacting transduction
137
What is cotransduction?
A mapping tool used with genes that are within 2 minutes of each other. This occurs because Phage can only take up very small pieces of bacterial DNA and sometimes 2 genes are packaged into the same phage.
The likelihood that 2 genes will be cotransduced depends on how close they lie to each other on the chromosome (far away genes do not cotransduce).
138
What is bacterial transformation?
Living bacterial cell takes up DNA released from a dead bacterium; can recombine w/ the live DNA to produce a new DNA sequence
139
What is natural transformation?
A natural process that has involved in certain bacteria; they can naturally pick up environmental DNA
140
What is artificial transformation?
Occurs due to experimental manipulation in which DNA uptake is forced
141
What are competent cells?
Bacterial cells that are able to take up environmental DNA. These cells carry competent factors.
142
What are competent factors?
In bacterial TRANSFORMATION, Factors that facilitate the binding of DNA fragments to the cell surface. They further facilitate the uptake and integration of DNA into the bacterial chromosome
143
What is the lysogenic cycle?
In the lysogenic cycle, the viral DNA gets integrated into the host's DNA but viral genes are not expressed. The prophage is passed on to daughter cells during every cell division. After some time, the prophage leaves the bacterial DNA and goes through the lytic cycle, creating more viruses
144
What is a heteroduplex?
During bacterial transformation, homologous recombination occurs in which the foreign bacterial DNA replaces one of the DNA strands of the host bacterial chromosome.
This results in a misalignment of alleles of the same gene which is called a heteroduplex.
145
In bacterial transformation, what happens to the heteroduplex?
DNA repair enzymes in the recipient cell recognize the mismatches and repair them. This can result in a new genotype.
146
In transformation, what is non-homologous recombination?
Occurs when a DNA fragment that has entered the cell may not match any genes already on the bacterial chromosome. Thus the foreign DNA strand is incorporated randomly.
147
What is Horizontal Gene Transfer?
A process in which an organism incorporates genetic material from another organism wihtout being an offspring. This can occur between the same or different species.
148
What are viruses?
Non-living particles with nucleic acids
149
What is Viral Host Range?
Number of species/cell types viruses can infect.
150
What is a Viral Capsid?
A protein coat that encloses the viral genome; the subunits are capsomers.
151
What is a viral envelope?
A lipid bilayer derived from the plasma membrane of host cell. It is embedded with virally encoded spike glycoproteins and encloses the cell.
152
What types of viruses commonly have viral envelopes?
Viruses that infect eukaryotic cells
153
What is reverse transcriptase?
Converts RNA to DNA. This allows a virus with a RNA genome to inegrate with a host the has a DNA genome.
154
What is a prophage?
A prophage is an inactive bacteriophage which is inserted into a host's chromosome
155
What is a provirus?
A provirus is a virus genome that is integrated into the DNA of a host cell (eukaryotic)
156
How are prophage and provirus different?
The main difference between prophage and provirus is thatprophage is the viral genome integrated into a bacterial genome, whereas provirus is the viral genome integrated into a eukaryotic genome
Furthermore, prophages are bacteriophages which undergo the lysogenic cycle by integrating its genome into the bacterial genome while proviruses are retroviruses that convert their single-stranded RNA genome into double-stranded DNA, integrating into the eukaryotic genome.
In addition, prophage can undergo excision from the host genome in order to enter into the lytic cycle while provirus may not undergo excision after splicing.
157
What is a temperate phage?
Temperate phages are bacteriophages that can choose between the lytic and the lysogenic pathways of development
