Nilson Flashcards
(100 cards)
1
Q
Euploids and examples?
A
Organisms with multiples of the basic chromosome set(genome)
2
Q
Normal euploids?
A
Haploid and Diploid
3
Q
Aberrant euploidy?
A
Changes in chromosome sets, organisms have more or fewer than the normal number of sets
4
Q
Polyploids?
A
Individual organisms that have more than two chromosome sets (3n, 4n, 5n)
5
Q
Ploidy?
A
Number of chromosomes in a set
6
Q
Monoploids?
A
An individual member of a normally diploid species only have one chromosome set
7
Q
Why do monoploid zygotes fail to develop?
A
Because members of a diploid species carry a number of deleterious recessive alleles that are normally masked by wild-type alleles but now can be observed
8
Q
Why are monoploids sterile?
A
Chromosomes have no pairing partners for meiosis
9
Q
T/F: Plants are more tolerant to polyploidy?
A
True
10
Q
Autopolyploidy?
A
Multiple chromosome sets originating from within one species
(the chromosomes are fully homologous and can pair during meiosis)
11
Q
Allopolyploidy?
A
Multiple chromosome sets from closely related species(chromosome are only partly homologous)
12
Q
T/F: The more copies of chromosomes the larger the organism?
A
True
13
Q
How do triploids arise?
A
Cross between 2n and 4n
(n + 2n gametes)
14
Q
Chemical that can cause spontaneous doubling?
A
Colchicine
15
Q
How does colchicine lead to spontaneous doubling?
A
Colchicine disrupts microtubule formation which prevents the sister chromatids from being separated
16
Q
Somatic consequences of polyploidy?
A
- Lethality(mainly in animals)
- Increased size
17
Q
Germline consequences of polyploidy?
A
Sterility
18
Q
How to generate euploid gametes from a triploid?
A
All three chromosomes move into the same cell
19
Q
What is the probability of euploidy in a triploid?
A
P = (1)(1/2)(1/2)
1: chromosome 1 goes into either cell
1/2: chromsome goes into same cell as one
1/2: chromosome goes into same cells as one and two
20
Q
Causes of autopolyploidy?
A
- Induced/intentional
(colchicine, selective breeding) - Spontaneous(dispermy, error in meiosis)
21
Q
How do you get more seedless(3n) watermelon?
A
Breeders must go back to the 4n and 2n cross each time they want a 3n watermelon
22
Q
Dispermy?
A
When one egg is fertilized by two sperm this results in a triploid gamete
23
Q
Advantage of triploids?
A
They are parthenogenetic meaning they can reproduce without mating
24
Q
Aneuploid?
A
Organisms whose chromosome number differs from the wild type by part of a chromosome set(can be greater or less)
25
Viable trisomies(2n +1)?
XXX, XXY, XYY or trisomy 21
26
Viable monosomy(2n -1)?
XO, missing one copy of a sex chromosome
27
Amphiploid?
An allopolyploid formed from the union of two separate chromosome sets and their subsequent doubling
28
Most common cause of aneuploidy?
Nondisjunction
29
What is nondisjunction?
Failure of normal segregation of homologous chromosomes to opposite poles at meiotic/mitotic divisions
30
Why does nondisjunction occur in meiosis I more often than meiosis II?
Since homologous chromatids of the tetrad have to remain paired. Whereas in meiosis II centromere is just split
31
T/F: Monosomies in humans for autosomes are deleterious?
Yes, they die in utero
32
Turner syndrome?
Characterized by the monosomy(XO), 44 autosomes and 1 X chromosome. Sterile females
33
Describe the polyploid jimson weed plant?
proportioned like a normal diploid, only larger due to the extra sets of chromosomes.
34
Describe the aneuploid jimson weed plant?
Disproporitionate compared to the wild-type plant
35
Euploid gene balance?
Ratio of genes on any one chromosome to the genes on the other chromosomes is always 1:1
36
Aneuploid gene imbalance?
aneuploid the ratio of genes on the aneuploid chromosome to genes on the other chromosome differs from the wild type up or down by 50%.
37
Gene dosage effect?
More copies of genes = more transcripts = more protein product made
38
Why are aneuploids disporportionate compared to polyploids?
Polyploids maintain a 1:1 ratio of genes in the cell, they just have more. Aneuploids do not maintain a 1:1 ratio of genes in cells which causes more of one gene to be transcribed which effects phenotypic characteristics encoded by that gene
39
Why is having too few gene products(monosomy) much worse for an organism than having too many gene products(trisomy)?
Deleterious recessive mutations are no longer masked
40
Y vs X chromosome genes?
Y chromosome: contains very few functional genes, mainly for sex determination
X chromosome: contains all the housekeeping genes
41
Why are XXX humans are phenotypically normal?
They only have one active X chromosome
42
Why are XXY individuals abnormal?
A few genes scattered through out the inactive X are still transcriptionally active. Compared to XY males the X gene is transcribed at twice the level
43
What about the inactive X chromosome in XXX individuals?
In XXX females the X gene is transcribed 1.5 times more than in XX females
44
Why is turner syndrome (XO) so severe?
Due to the deleterious effects of monosomy for the X chromosomes and lower activity of the transcribed genes of X
45
Types of rearrangements?
Deletion: loss of chromosome segment
Duplication: doubling of chromosome segment
Inversion: orientation of a segment within the chromosome is reversed
Translocation: segment moves to a different chromosome
46
Causes of rearrangments?
Caused by either DNA breakage or crossing over between repetitive DNA
47
DNA breakage +what induces them?
Both DNA strands must break at two different locations, followed by a rejoining of the broken ends to produce a new chromosomal arrangement
These can be induced by using ionizing radiation
48
Crossing over leading to rearrangments?
Nonallelic homologous recombination: crossing over between short homologous units found at different chromosomal loci
49
The only chromosomal rearrangments that survive meiosis?
those that produce DNA molecules that have one centromere and two telomeres
50
Accentric Chromosome?
lacks a centromere, a rearrangement that produces this causes the chromosome to not be dragged to either side of the pole and not incorporated into either nucleus. Accentric chromosomes are not inherited
51
Dicentric chromosomes?
-Two centromeres
These chromosomes are often pulled simultaneously to opposite poles at anaphase, forming an anaphase bridge
52
Lacking telomeres?
If chromosome breaks create chromosomes lacking telomeres, DNA will be progressively lost from the end of the chromosome with every round of replication.
53
What is an unbalanced rearrangement?
Change the gene dosage of a chromosome segment
54
Causes of unbalanced rearrangements?
1. Deletions
2. Duplications
55
Balanced Rearrangements?
Change the chromosomal gene order but do not remove or duplicate any DNA (genes are in balance)
56
Intragenic deletion?
small deletion that occurs within a gene
Inactivates the gene and has the same effect as that of other null mutations of that gene
If the homozygous mutant phenotype is viable so will the homozygous deletion
57
Multigenic deletions?
-Several deletions in genes
More severe consequences than intragenic
Results in disruption of normal gene balance
Small deletions are sometimes viable in combination with a normal homolog
58
What is a deletion loop?
A loop that forms in a wild-type chromosome during meiosis when paired with its homolog that is missing a part of its chromosome. The wild-type chromosome loops out the part missing in the other chromosome
59
Clues to indicate deletions?
-Presence of a recessive mutant phenotype
-Looping out during meiosis
60
Tandem duplication?
duplicate regions are located next to each other
61
Insertional duplication?
duplicate regions are located elsewhere in the genome
62
Duplication heterozygote?
Diploid cell containing a duplication will have three copies of the chromosome region in question(two in one chromosome and one in the other). Forms a loop during meiosis
63
High levels of duplication in the genome benefits?
Plays an important role for non allelic homologus recombination that leads to various chromosomal rearrangements. Led to development from ape to homo sapien
64
Intrachromosomal duplication?
Duplicated units dispersed within the same chromosome
65
Interchromosomal duplication?
Duplicated units found on other chromosomes
66
Paracentric inversion?
centromere is outside of the inversion
67
Pericentric inversion?
centromere is involved in the inversion
68
T/F: Individuals with inversions are generally normal unless the inversion occurs within a gene?
True
69
Inversion heterozygote?
only one chromosome contains the inversion
70
Inversion Loop?
-Occurs during meiosis
-One chromosome twists once at the ends of the inversion to pair with its untwisted homolog
71
how can pericentric inversions be detected?
through new arm ratios
72
Adjacent segregation?
Occurs in reciprocal translocations meiosis. When one normal chromosome is segregated with a translocated chromosome, this produces inviable gametes. Each gamete contains a deletion and duplication of gene products.
73
Alternate segregation?
Occurs in reciprocal translocations meiosis. When the two normal chromosomes are segregated together and the two translocated ons are segregated together. These produce 100% viable gametes because the products are fully balanced
74
Nondisjunction during meiosis I results?
100% aneuploid gametes
-1n + 1
-1n-1
75
T/F: Mutations that block crossing over tend to lead to nondisjunction?
True
76
Nondisjunction during meiosis II results ?
50% anueploid gametes
- one 1n+1 gamete
-one 1n -1 gamete
77
Inversion between genes?
Not harmful and does not dirupt gene function
78
Inversion between one gene and within a gene?
Disrupts the one gene, depending on what that gene does determines the phenotype
79
Inversion between two genes?
Two genes are fused can result in a non-functional fusion gene, oncogene or productive new function
80
Colorless alleles found in maize?
C conditions a blue pigment in kernels
c does not make blue pigment(yellow kernels)
Cā is a dominant inhibitor that represses pigment production, dominant to C
81
Retrotransposons?
Transposable elements that employ reverse transcriptase to transpose through an RNA intermediate
82
Crossing a wild-strain female with a lab stain male?
F1 are phenotypically normal and able to reproduce
83
Crossing a wild-strain male with a lab strain female?
F1 progeny are dysgenic
84
T/F: Variation in genome size results from the variation in the numbers of repetitive sequences and not the numbers of genes
True
85
Majority of the transposable elements in humans?
Long interspersed elements (LINEs)
Short interspersed elements(SINEs)
86
Why are transposable elements in yeast more likely to cause harm?
Almost 70% of the yeast genome is exons which means there is a high probability the transposable elements will disrupt a coding sequence
87
Point mutation?
single-base-pair change in DNA sequence
88
Three types of point mutations?
Base substitutions
Base insertions
Base deletions
89
Base substitutions?
Mutations in which one base is replaced by another
90
Transition base substitutions?
Replace a purine with a purine(G to A) or a pyrimidine to a pyrimidine(C to T)
91
Transversion base substitutions?
Replaces a pyrimidine with a purine(G to C/A to T)
92
Synoymous mutations?
Change the sequence of a codon but not the encoded amino acid
93
Missense mutations
Change the sequence of a codon and the amino acid encoded by it
94
Conservative missense mutation?
result in an amino acid being replaced by a structurally similar amino acid
95
Nonconservative missense mutation?
Result in an amino acid being replaced by a chemically different amino acid
Likely to produce a change in the protein's structure/function
96
Nonsense mutation?
Change the sequences of a codon that codes for an amino acid into one that stops translation
97
Where does the nonsense mutation have occur to have the least affect on the protein?
closer a nonsense mutation is to the 3ā end of the ORF, the more likely the resulting protein will retain its biological activity
98
What type of mutations lead to frameshift?
Indels
99
Indels of three base pairs?
do not cause frameshifts, just addition/loss of an amino acid
100
