Lecture 9a Flashcards
What are homologous genes?
Two or more genes derived from a common ancestor.
What is different about homologous genes between them?
They may have similar but distinct functions due to accumulation of genes.
What are paralogs?
Homologous genes within a single species.
What is an example of paralogs?
The globin genes, which encode subunits of proteins that bind oxygen.
How many globin gene paralogs are there? On how many chromosomes?
There are 14 paralogs on 3 different chromosomes.
What are the similar and different functions that different paralogs carry out?
1) All bind oxygen
2) Myglobin stores oxygen in muscle cells
3) Different globins are in the red blood cells at different developmental stages based on the oxygen needs of the developing individual.
What are the 3 different globin chromosomes that arose from the ancestral globin?
1) Myoglobins
2) Alpha chains (2)
3) Beta chains (2)
Where do the alpha and beta chains come from?
Hemoglobins
What is Copy Number Variation?
When sections of the chromosome are tandemly repeated. The number of repeats in the genome varies between individuals.
How much of the human genome is subject to copy number variations?
Approximately 5% of the human genome is subject to copy number variations.
What is this image showing?
Copy Number Variation
What is Cytogenetics?
The field of genetics involving microscopic examination of chromosomes from a cell or organism.
What 2 things does cytogenetics allow for?
1) The detection of individuals with abnormal chromosome number or structure.
2) Provides a way to distinguish between two closely-related species.
What is G-banding?
When chromosomes are exposed to the Giemsa dye. Some regions bind the dye heavily (darker bands) and some do not bind it well (lighter).
What is the dye binding in G-banding?
Proteins are being stained.
Why do we treat chromosomes with dye?
Many chromosomes have the same size and centromere position, so we can use dye to produce characteristic binding patterns.
Which has more bands: prometaphase or metaphase chromosomes?
Prometaphase, because they are not as condensed as metaphase and chromosomes condense as mitosis goes on.
Which are more condensed: anaphase or metaphase chromosomes? So, which has less bands?
Anaphase is more condensed, thus, it has less bands.
Besides banding pattern, how are chromosomes classified in cytogenetics?
Chromosomes are classified by their centromere position.
What is a metacentric chromosome?
The centromere is very close to the middle (no chromosomes is perfectly metacentric).
What is a submetacentric chromosome? What species do we see this in?
The centromere is off slightly to the side. Most humans have these.
What is an acrocentric chromosome?
One arm of the chromosome is shorter than the other, thus, it has less genes.
What is a telocentric chromosome? Who does and does not have these?
The centromere is completely off to one side. Humans don’t have them. All of chromosomes in mice are.
What is a Robertsonian Translocation?
The long arms of 2 acrocentric chromosomes and fuse them.
How many live human births display Robertsonian translocations?
1/900
What is one example of a Robertsonian translocation?
Familial Down Syndrome
In Familial Down Syndrome, what chromosomes are the translocation always between?
Chromosomes 14 and 21
How many births does Down Syndrome affect?
1/700 births
What percentage or fraction of Down Syndrome is Familial Down Syndrome?
About 5% or 1/14,000 births
When does Familial Down Syndrome occur?
When there are 3 copies of chromosome 21
When does unbalanced lethal combinations occur?
Where there are more than 2 copies of 14 or we are less than 2 copies of 14 or 21.
What is deletion?
Chromosomal bands get deleted.
What is duplication?
Chromosomal bands get repeated.
What is inversion?
Chromosomal band gets flipped.
What is simple translocation?
Chromosomal band moves location on the chromosome.
What is reciprocal translocation?
Two chromosomes swap bands.
What usually causes a chromosomal duplication? What does this cause on the other chromosome?
Abnormal recombination in which there is a misaligned crossover. Duplication on one chromosome, deletion on the other.
What are two ways to obtain reciprocal translocations? Which is more common?
1) Chromosomal breakage and DNA repair through NHEJ incorrectly connects them.
2) Nonhomologous chromosomes will have regions of homology between them and crossover will occur. MORE COMMON.
While human and chimp chromosomes are VERY similar, what is the one difference? Who is the oddball?
We have submetacentric chromosomes while chimps have acrocentric chromosomes. Humans are the oddball because all other species look like chimps’ chromosomes.
Where do we hybridize the fluorescent probe to?
We take a metaphase chromosome, unwind the protein, and anneal the probe to the unwound DNA/chromosome.
Describe the steps of hybridizing a fluorescent probe to a mitotic chromosome.
1) We take the probe DNA and label it with fluorescent molecule.
2) Denature the probe DNA.
3) Unwind the mitotic chromosomes and anneal the probe (Hybridize)
4) Visualize the mitotic chromosomes with the annealed fluorescent probe.
What does DNA FISH stand for?
DNA Fluorescent In Situ Hybridization
What is DNA Fish?
We hybridize DNA fluorescent to mitotic interphase chromosomes.
What is an example of a specific translocation that occurs frequently?
The Philadelphia chromosome in Chronic Mylogenous Leukemia (CML).
What is the incidence of the Philadelphia chromosome?
1-2 per 100,000 people.
What did FISH allow us to do in terms of the Philadelphia chromosome?
We were able to detect the translocation that produces the Philadelphia chromosome.
If we wanted to recognize entire chromosomes, what can we purchase?
There are FISH probes we can purchase, called chromosome paints, that will recognize entire chromosomes.
What is Spectral Karyotyping (SKY)?
Every chromosome has a differently colored chromosome paint.
T/F: When chromosomes are not condensed for mitosis or meiosis, they occupy domains in the nucleus.
True.
