Chromosome Changes (Lec 11) Flashcards
Findings suggest that Down Syndrome is not due to a single gene but is caused by complex interactions among multiple genes that are affected when an extra copy of which chromosome is present?
21
Duplications, deletions, inversions, and translocations are all type of what?
chromosome rearrangements
True or False?
In a chromosome inversion, a segment of the chromosome is turned 180 degrees
true
Type of duplication in which the duplicated region is immediately adjacent to the original segment. Ex. AB*CDEFGefg
tandem duplication
Type of duplication in which the duplicated region is located some distance from the original segment, either on the same chromosome or on a different one. EX. AB*CDEFGab
displaced duplication
A duplication in which the duplicated region is inverted. Ex. ABba*CDEFG
reverse duplication
What causes unequal crossing over of wild type chromosomes and what is the result?
chromosomes that do not align properly; results in one chromosome containing a duplication and the other chromosome containing a deletion
What is the result of unequal crossing over between bar chromosomes (each have two copies of Bar)?
a chromosome with three Bar copies and a wild type chromosome
In regards to chromosome rearrangement, why can a large deletion be easily detected?
the chromosome is noticeably shortened and the normal chromosome must loop out during the pair of homologs
In regards to chromosomal rearrangements, what are the effects of deletions?
imbalances in gene product, expression of a normally recessive gene, haploinsufficency
This type of deletion is a series of X-linked wing mutations in drosophila that can act as a recessive lethal
Notch
In what phase of meiosis does the normal chromosome loop out in order to allow for correct pairing and alignment between chromosomes?
prophase I
What does Notch code for?
a receptor that transmits signals received from outside the cell to the cell’s interior
Loss of all copies of Notch gene prevents normal development, acting as what?
a recessive lethal
In regards to chromosome rearrangement, specifically inversion, what is the type of inversion that does not include the centromere?
Paracentric inversion
In regards to chromosome rearrangement, specifically inversion, what is the type of inversion that includes the centromere?
Pericentric inversion
note: “i” in pericentric is for “includes” centromere
ABCDEFG to ABCFEDG is an example of what type of chromosome rearrangement?
Paracentric inversion
ABCDEFG to ADCBEFG is an example of what type of chromosome rearrangement?
Pericentric inversion
ABCDEFG to ABCDEFGEFG is an example of what type of chromosome rearrangement?
Tandem duplication
ABCDEFG to ABCDEFGAB is an example of what type of chromosome rearrangement?
Displaced duplication
ABCDEFG to ABBACDEFG is an example of what type of chromosome rearrangement?
Reverse duplication
How is translocation different from crossing over?
Crossing over is the exchange of genetic material between homologous chromosomes while translocation involves the transfer or movement of genetic material between non-homologous chromosomes.
In regards to a pairing of a WT chromosome with a chromosome containing paracentric inversion in a heterozygous individual, formation of an inversion loop and thus crossing over with inversion results in an unusual structure. Describe the chromatids of this structure after this occurs
One of the four chromatids has two centromeres, one lacks a centromere
In regards to a pairing of a WT chromosome with a chromosome containing paracentric inversion in a heterozygous individual, in anaphase I, the centromeres separate, stretching the dicentric chromatid which breaks. What happens to the chromosome lacking a centromere?
it is lost
In regards to a pairing of a WT chromosome with a chromosome containing paracentric inversion in a heterozygous individual , what are the resulting gametes like after anaphase II?
two gametes contain nonrecombinant chromosomes: one WT and one with inversion; the other two chromosomes contain recombinant chromosomes that are missing some genes
True or False?
The resulting recombinant gametes from inversion in a heterozygous individual are still viable.
false; they are nonviable due to missing genes
In regards a pairing of a WT chromosome with a chromosome containing pericentric inversion in a heterozygous individual, describe the unusual structure that is formed, specifically the chromatids.
two of the resulting chromatids have too many copies of some genes and no copies of others
In regards to inversions in meiosis, do homozygous individuals have problems during meiosis?
no, only heterozygous individuals
Heterozygous individuals demonstrate reduced recombination in ____ inversion, as gametes formed result in nonviable offspring and have abnormal gametes formed in ___ inversion.
paracentric; pericentric
_____ entails the movement of genetic material between non-homologous chromosomes
translocation
This type of translocation is more common and involves the movement of material between non homologous chromosomes
reciprocal translocation
This type of translocation involves the movement of genetic material from one chromosome to another without any reciprocal exchange
non-reciprocal translocation
Robertsonian translocation results in what?
a large metacentric chromosome and a fragment that often fails to segregate and is lost
In prophase I when alignment of chromosomes occurs, what kind of structure is formed for translocation
a crosslike configuration that allows homologous sections from one chromosome to match to two other chromosomes
In regards to translocation segregation patterns, in anaphase I, the chromosomes separate in how many different ways?
one of three different ways:
alternate segregation
adjacent-1 segregation
adjacent-2 segregation (rare)
Out of the three types of translocation segregation, which type produces viable gametes after anaphase II?
only alternate segregation; gametes resulting from adjacent-1 and adjacent-2 segregation are nonviable because some genes are present in two copies, whereas others are missing
Fragile-X syndrome is named after a fragile site on the human X chromosome. What are some characteristics of the syndrome?
mental retardation; x-linked inheritance; 1 in 1250 male births; results from an increase in the number of repeats of a CGG trinucleotide
What does G banding reveal?
bands rich in A-T base pairs
What does Q banding reveal?
difference in relative amounts of C-G and A-T base pairs
What does C banding reveal?
regions with centromeric heterochromatin
What does R banding reveal?
bands rich in C-G base pairs
What is the genetic basis of Cri-du-chat syndrome and what is the phenotype?
deletion on short arm of chromosome 5; infants often have a high-pitched cry, also characterized by intellectual disability and delayed development, small head size, low birth weight and weak muscle tone. Some children are born with a heart defect
What is the genetic basis of Wolf-Hirschhorn syndromee and what is the phenotype?
chromosome deletion on short arm of chromosome 4; distinct craniofacial phenotype, growth and mental retardation, seizures, heart defects
What is the genetic basis of Williams-Beuren syndrome and what is the phenotype?
deletion on short arm of chromosome 7; facial features, heart defects, mental impairment
What is the genetic basis of Prader-Wili syndrome and what is the phenotype?
deletion on short arm of chromosome 15; feeding difficulty at early age, but becoming obese after 1 year
