Chapter 6: Chromosome Variation Flashcards
What are the six types of chromosome mutations?
- Rearrangement
- Aneuploidy
- Polyploidy
- Deletion
- Inversion
- Translocation
How does rearrangement affect a chromosome?
Takes place within a chromosome
Ex: ABCD -> ABCDCD
What is aneuploidy?
Change in the number of individual chromosomes
What is polyploidy?
Change in number of chromosome sets
What is deletion mutation?
The removal of a gene
Ex: ABCD -> ABC
What is an inversion mutation?
When a chromosome “flips around.”
Ex: ABCR –> ABЭЯ
-Э = reverse C
-Я = reverse R
What is the translocation mutation?
When genes change chromosomes
Ex: ABCD is on one chromosome, and EFGH is on another chromosome
Original:
-ABCD
-EFGH
Translocated:
-ABGH
-EFCD
What is a paracentric inversion?
An inversion of genes without the use of centromeres
pArAcentric,think of “a for absent”
How does paracentric inversion lead to non viable offspring?
The resulting recombinant gametes are nonviable because they are missing some genes
What is pericentric inversion?
Inversions that includes a centromere
How does pericentric inversion cause nonviable offspring?
The recombinant gametes are nonviable because genes are either missing or present in too many copies.
What are the steps that take place in paracentric inversion that lead to missing genes? (7 steps)
- Two chromosomes; one has wild-type, and the other has a paracentric inversion
- In prophase I, an inversion loop forms
- A single cross-over takes place within this inverted loop
- The cross-over produces an unusual structure
- Out of the four chromatids produced, one has two centromeres, and one has no centromeres
- In anaphase I, as the centromeres separate, the chromatid with two centromeres is stretched too far and breaks apart; the chromatid with no centromeres is lost
- Resulting gametes are missing genes
What are the steps that take place in pericentric inversion that lead to missing genes or too many genes? (5 steps)
- Two chromosomes, one with wild-type and one with pericentric inversion
- In prophase I, an inversion loop forms
- Crossing-over takes place within the loop
- Two of the resulting chromatids have too many of some genes and are missing other genes
- The chromatids separate in anaphase II forming 4 gametes that have too many or too little of genes
What is the difference between euploid and aneuploid?
Euploid: multiples of basic chromosome set
Aneuploid: chromosome number not a multiple basic set
What are the 4 types of aneuploidy?
- Nullisomy
- Monosomy
- Trisomy
- Tetrasomy
Define nullisomy and how it’s expressed mathematically (Ex: 2n +/- ?)
Loss of both members of a homologous pair of chromosomes
2n - 2
Define monosomy and how it’s expressed mathematically (Ex: 2n +/- ?)
Loss of a single chromosome
2n -1
Define trisomy and how it’s expressed mathematically (Ex: 2n +/- ?)
Gain of a single chromsome
2n + 1
Define tetrasomy and how it’s expressed mathematically (Ex: 2n +/- ?)
Gain of two homologous chromosomes
2n + 2
What are the two categories of polyploids?
- Autopolyploid
- Allopolyploid
Define autopolyploid
When an organism has more than two sets of chromosomes from the same species
Define allopolyploid
When an organism has more than two sets of chromosomes from different species
During meiosis, errors can occur during chromosome replication. Which term describes the addition of genetic material to a chromosome through extra replication of a chromosomal section?
A) Translocation
B) Nondisjunction
C) Duplication
D) Isochorome mutation
C) Duplication
Which term describes the process of sister chromatids not separating at the centromere during cell division?
A) Aneuploidy
B) Cytokinesis
C) Desegregation
D) Nondisjunction
D) Nondisjunction
Which term describes the rearranging of genetic material between nonhomologous chromosomes without a net loss or gain of genetic material?
A) Translocation
B) Crossing over
C) Inversion
D) Frameshift
A) Translocation
Which term describes a mutation where a chromosome breaks and its genetic material is reinserted in a different orientation?
A) Frameshift
B) Inversion
C) Duplication
D) Isochromosome
B) Inversion
If the wild type chromosome is AB * CDEFG and results in AB * CDEFDEFG what kind of chromosomal mutation occurred?
Tandem Duplication of DEF
(Tandem just means right after. It goes DEFDEF)
If the wild type chromosome is AB * CDEFG and results in AB * CDEFCDEFG what kind of chromosomal mutation occurred?
Displaced duplication of DEF
(Displaced means it did not occur right after. Instead of DEFDEF (tandem), it’s DEF C DEF)
If the wild type chromosome is AB * CDEFG and results in AB * CDE what kind of chromosomal mutation occurred?
Deletion of FG
If the wild type chromosome is AB * CDEFG and results in AB * CGFED what kind of chromosomal mutation occurred?
Paracentric inversion that includes DEFG
If the wild type chromosome is AB * CDEFG and results in AEDCB*FG what kind of chromosomal mutation occurred?
Pericentric inversion of BDCE
Which of the following statements explains why duplication is a driving force for evolution and the generation of new genes (Multiple correct statements)
- Duplicated genes provide extra copies of DNA that are not constrained by an essential function
- Genes duplicate and then diverge from the original sequence to create multigene families
- Duplication of a gene segment always results in novel phenotypes
- Phenotypic variation can occur when fixed random mutations are introduced into the new chromosomal environment
Statements 1, 2, and 4
- Duplicated genes provide extra copies of DNA that are not constrained by an essential function
- Genes duplicate and then diverge from the original sequence to create multigene families
- Phenotypic variation can occur when fixed random mutations are introduced into the new chromosomal environment
Which mutations can a geneticist identify with the G-banding technique? (2 correct responses)
- A nonsense mutation introducing a premature stop codon into a gene on chromosome 5
- A reciprocal translocation of parts of chromosome 1 and chromosome 11
- A single nucleotide substitution in which A replaces C on chromosome 2
- A deletion of half of the long arm on chromosome 20
- A translocation of a region of the short arm between sister chromatids
2, and 4
- A reciprocal translocation of parts of chromosome 1 and chromosome 11
- A deletion of half of the long arm on chromosome 20
Select the statements that describe the effects of copy number variation on human phenotypes. (3 correct responses)
- Copy number variations are associated with polygenic disorders such as schizophrenia
- Oncogene overexpression due to a gain in copy number can cause cancer
- An increase in copy number can cause Mendelian autosomal disorders due to point mutations
- An increase in the copy number of immunity genes can result in increased pathogen resistance
- A decrease in copy number can cause gene function loss due to chromosome breaks
1, 2, and 4
1-Copy number variations are associated with polygenic disorders such as schizophrenia
2-Oncogene overexpression due to a gain in copy number can cause cancer
4-An increase in the copy number of immunity genes can result in increased pathogen resistance
A man had a large inversion on one of his chromosomes. How might this impact his offspring?
A) Minor genetic abnormalities due to minimal deficient in genetic materials
B) Server phenotypic abnormalities caused by unbalanced chromatids
C) Fewer autosomes because normal synapsis during meiosis does not occur
D) No impact because all genetic information is retained
B) Server phenotypic abnormalities caused by unbalanced chromatids
Two nonhomologous chromosomes are in the following order:
Chromosome 1: AB * CDEFG
Chromosome 2: RS * TUVWX
The chromosomes undergo translocation and result in the following product:
Chromosome 1: AB * CD
Chromosome 2: RS * TUVWXEFG
Which type of translocation occurred?
Nonreciprocal trans location of EFG
(Non reciprocal meaning not in the same placement pattern)
Two nonhomologous chromosomes are in the following order:
Chromosome 1: AB * CDEFG
Chromosome 2: RS * TUVWX
The chromosomes undergo translocation and result in the following product:
Chromosome 1: AUVB * CDEFG
Chromosome 2: RS * TWX
Which type of translocation occurred?
Nonreciprocal translocation of UV
(nonreciprocal meaning not in the same placement pattern)
Two nonhomologous chromosomes are in the following order:
Chromosome 1: AB * CDEFG
Chromosome 2: RS * TUVWX
The chromosomes undergo translocation and result in the following product:
Chromosome 1: AB * TUVFG
Chromosome 2: RS * CDEWX
Which type of translocation occurred?
Reciprocal translocation of CDE and TUV
(Reciprocal meaning replacing each other in the same placement pattern. CDE went to where TUV was and vice versa)
Two nonhomologous chromosomes are in the following order:
Chromosome 1: AB * CDEFG
Chromosome 2: RS * TUVWX
The chromosomes undergo translocation and result in the following product:
Chromosome 1: AB * CWG
Chromosome 2: RS * TUVWDEFX
Which type of translocation occurred?
Reciprocal translocation of DEF and W
(Reciprocal meaning replacing each other in the same placement pattern. DEF went to where W was and vice versa)
Select the definition of aneuploidy.
A) The number of chromosome sets that make up a complete genome
B) A complete chromosome set or an exact multiple of the haploid chromosome set
C) The addition or loss of less than a full set of chromosomes or chromosome pairs
D) A chromosomal complement with at least three complete sets of homologous chromosomes
C) The addition or loss of less than a full set of chromosomes or chromosome pairs
Select the definition of euploidy.
A) The number of chromosome sets that make up a complete genome
B) A complete chromosome set of an exact multiple of the haploid chromosome set
C) The addition or loss of less than a full set of chromosomes or chromosome pairs
D) A chromosomal complement with at least three complete sets of homologous chromosomes
B) A complete chromosome set of an exact multiple of the haploid chromosome set
Select the definition of polyploidy.
A) The number of chromosome sets that make up a complete genome
B) A complete chromosome set of an exact multiple of the haploid chromosome set
C) The addition or loss of less than a full set of chromosomes or chromosome pairs
D) A chromosomal complement with at least three complete sets of homologous chromosomes
D) A chromosomal complement with at least three complete sets of homologous chromosomes
Define haploid
A single unpaired copy of each chromosomes
Define monosomic
Only one copy of a specific chromosome
What is meant by “n = 1”
A genome is composed of one unique chromosome
Two brothers have X-linked red-green colorblind vision, and their parents have full-color vision. The first brother’s karyotype is 47, XXY (Klinefelter syndrome), and the second brother’s karyotype is 46, XY.
In which parent and in what cell division phase did the first brother’s chromosomal nondisjunction occur? (Assume no recombination)
A) in the mother in meiosis II
B) In either parent in somatic cell mitosis
C) In the father in meiosis II
D) In the father in meiosis I
E) In the mother in meiosis I
A) in the mother in meiosis II
Explanation:
We know it’s in the mother because color blindness is an X-linked trait; we know it’s the mother’s X and not the father’s X because both brothers have color blindness, even though one only has 1 X from his mother.
We know it’s meiosis II and not meiosis I because nondisjunction at meiosis I form all aneuploidy (2n -1 and 2n +1) while nondisjunction of meiosis II one normal gamete and one aneuploidy gamete (2n, 2n +/- 1). In this case, the aneuploidy gamete is 2n+1 since we know the first brother is 47, XXY
Chromosome duplication and deletion frequently result in abnormal phenotypes or enviable gametes. Which factor is a major contributor to this phenomenon?
A) Gene dosage is modified
B) Additional copies unmask recessive diseases
C) The genes are found in a novel arrangement
Why are these effects less noticeable for multisomies and monosomies of the X chromosome in humans?
A) X inactivation only allows one X chromosome to be expressed in any given cell
B) The X chromosome is not necessary for human survival
C) The x chromosome only has a few genes
A) Gene dosage is modified
and
A) X inactivation only allows one X chromosome to be expressed in any given cell
Chromosome duplication often results in abnormal phenotypes because
a. Developmental process depend on the relative amounts of proteins encoded by different genes
b. Extra copies of the genes within the duplicated region do not pair in meiosis
c. The chromosome is more likely to break when it loops in meiosis
d. Extra DNA must be replicated, which slows down cell division
a. Developmental process depend on the relative amounts of proteins encoded by different genes
What is pseudodominance, and how is it produced by a chromosome deletion?
Pseudodominance is the expression of a normally recessive mutation. Is is produced when the dominant wild-type allele in a heterozygous individual is absent due to a deletion on one chromosome.
A dicentric chromosome is produced when crossing over takes place in an individual heterozygous for which type of chromosome rearrangement?
○ Duplication
○ Deletion
○ Paracentric inversion
○ Pericentric inversion
Paracentric inversion
What is the outcome of a Robertsonian translocation?
○ Two acrocentric chromosomes
○ One large chromosome and one very small chromosome with two very short arms
○ One large metacentric chromosome and one large acrocentric chromosome
Two large metacentric chromosomes
One large chromosome and one very small chromosome with two very short arms
A diploid organism has 2n = 36 chromosomes. How many chromosomes will be found in a trisomic member of this species?
37
Why are sex-chromosome aneuploidies more common than autosomal aneuploidies in humans and other mammals?
Dosage compensation prevents the expression of additional copies of X-linked genes in mammals, and there is little information in the Y-chromosome, so extra copies of the X and Y chromosomes do not have major effects on development. In contrast, there is no mechanisms of dosage compensation for autosomes, and so extra copies of autosomal genes are expressed, upsetting developmental processes and causing the spontaneous abortion of aneuploid embryos
Species A has 2n = 16 chromosomes, and species B has 2n = 14 chromosomes would be found in an allotriploid of these two species?
○ 21 or 24
○ 42 or 48
○ 22 or 23
○ 45
22 or 23
