Lab 1 Flashcards
What is a chromosome?
Structures made of DNA and protein that contain numerous genes which encode the proteins in our bodies
What is a karyotype & when is it done?
A karyotype is a photograph or diagram of all the
chromosomes in a cell arranged in a particular order.
Done at metaphase so the dyads are more condensed and easier to visualize.
What does a somatic cell contain?
A somatic cell contains 44 autosomes (nonsex
chromosomes), or 22 homologous pairs of
autosomes, and 2 sex chromosomes.
What is a homolog?
A single unduplicated chromosome. Each homolog is similar but not
identical to the other homolog in the pair
Another name for tetrad?
Bivalent & duplicated homologous chromosome pair.
Another name for dyad?
Duplicated chromosome
What is a centromere?
A condensed region on the chromosome that provides the attachment site for the kinetochore
What does colchicine do?
Inhibits microtubule formation required to form the spindle fibers so that mitosis does not proceed past metaphase.
Turner syndrome
Only one X and no Y chromosome.
How are chromosomes distinguished from one another?
Size, Location of centromere, and banding patterns.
Location of centromere:
Metacentric – centromere is near the middle
Submetacentric – centromere is slightly off center
Acrocentric – centromere is significantly off center
Telocentric – centromere is at the end.
What are primary constrictions?
What are secondary constrictions?
Centromere
They are usually the site of rRNA gene.
How are chromosomes stained?
They are stained using a Giesma stain
Chromosome abnormalities involving one chromosome?
Deletion: part of the chromosome is absent.
Duplication: section of chromosome is repeated
Inversion: section of chromosome is upside down.
Chromosome abnormalities involving two chromosomes?
Simple Translocation: A piece of a chromosome is attached to another chromosome.
Reciprocal Translocation: Two different chromosomes exchange pieces.
What is crossing over?
Genetic exchange that occurs during meiosis. It occurs between two chromosomes that are the same number.
Occurs between duplicated chromosomes in a tetrad.
Familia type of Down syndrome
Not caused by nondisjunction.
Caused by Translocation.
Involves chromosomes 14 & 21.
Hypotonic Solution
Low solute concentration, high water concentration.
In karyotyping, they make the cell swell, this separates the chromosome so that they are easier to count.
What is Nondisjunction?
Failure of chromosomes to separate normally during cell division.
Two Types of Chromosomal Inversion-
Pericentric Inversion- Includes the centromere.
Paracentric Inversion- Doesn’t include the centromere
Position Effect
The expression of a gene can be altered, and the gene itself remains intact.
With a position effect, you are changing the physical
position of the gene on the chromosome, and that
change affects the expression of the gene.
Silencer/Condensed region
Example of a position effect.
Condensed region: Genes in highly
condensed regions of the chromosome are not expressed well.
Silencer: Genes are not expressed when they should be.
Enhancer
A sequence that increases transcription, so the gene would be overexpressed.
What are telomeres?
Repeated sequences on the ends of chromosomes that prevents chromosomal ends from attaching to one another.
Reactive end
When the telomere breaks, a reactive end is formed. The reactive ends can be joined by DNA repair enzymes to create translocation between two nonhomologous chromosomes.
Why might down syndrome occur? (Trisomy 21)
It might occur when crossing over does not take place between homologous chromosomes during meiosis during prophase 1.
What is Robertsonian Translocation?
Translocation that can occur between any acrocentric chromosomes that are numbered.
This can lead to down syndrome.
Fertilization with gamete 1: Monosomy 21 develops
Fertilization with gamete 2: Familial down syndrome.
A type of Hemophilia occurs _____
On genes that encode blood clotting factors.
The gene is located on the X chromosome.
It involves an Inversion.
The first step of gene expression:
Transcription.
When a chromosome that is not a sex chromosome is lost, it is always lethal. (True/False)
True
What is nondisjunction?
what can it result to?
An event in which the chromosomes do not segregate properly.
This can result in a change in chromosome number.
What is an alloploid organism?
An organism that contains sets of chromosomes from two or more species.
Types of nondisjunction?
Meiotic non-disjunction: Occurs during meiosis.
Mitotic non-disjunction: Occurs during mitosis.
Ways in which chromosome numbers can vary?
Mitotic non-disjunction
Meiotic non-disjunction
Alloploid.
Complete nondisjunction:
All chromosomes undergo nondisjunction and migrate to one of the daughter cells.
When do abnormalities in chromosomes normally occur?
After fertilization takes place.
What is mosaicism?
When an organism contains a subset of cells that are genetically different from those of the rest of the organism.
This depends on the timing and location of the original abnormal event.
What is autopolyploid?
An increase in the number of chromosomes set within a single species.
what is a Metacentric chromosome?
A chromosome that has equally centered centromere with arms with equal lengths.
what is a sub-metacentric chromosome?
A chromosome that has arms a bit off-centred, with arms that are distinctly unequal in length.
what is an acrocentric chromosome?
Centromeres are located nearer to one end than to the other. The arms are unequal in length.
What is used to show karyotype bands?
Giemsa Bloodstain.
G-Q-R bands.
Each homolog is ________ but not
_________to the other homolog in the pair
Similar; Identical
What is a centromere
A condensed region on the chromosome that
provides the attachment site for the kinetochore.
Kinetochore:
Group of proteins that attach to the centromere. They
pull the sister chromatids apart during cell division.
How to distinguish chromosomes from one
another:
Size, banding pattern & Location of centromere.
Karyogram
The display of the karyotype
What causes cru Du Chat?
Chromosomal deletion of chromosome 5.
Region on p arm is deleted.
