Chapter 8 Flashcards
Define Euploidy
Normal amount of chromosomes (46)
Define Aneuploidy
Abnormal amount of chromosomes
Define monosomy
Missing 1 chromosome
Define trisomy
Having 1 extra chromosome (tri = 3)
Generally, what occurs when a fetus has autosomal aneuploidy?
Death of the offspring in utero
What are the examples in which trisomy in autosomes survive?
Trisomy 21 (Down syndrome)
Trisomy 13 (Patau Syndrome)
Trisomy 18 (Edwards Syndrome)
Which type of chromosome tolerates aneuploidy better? What happens?
Sex chromosomes
Abnormal sexual development occurs but is not usually lethal.
What sex chromosome tolerates aneuploidy better and why?
X-chromosome as they can have X-inactivation occur.
How does aneuploidy occur?
During nondisjunction when chromosomes/chromatids don’t separate properly in meiosis I or II
Define deletion
When part of a chromosome is lost/deleted
Define terminal deletion
When deletion occurs at te end of the chromosome
Define intercalary deletion
When center of chromosome is deleted
How does intercalary deletion occur (3 steps)
- DNA forms a loop
- Edges of the loop breaks (dsDNA breaks)
- Broken edges are sealed back together
Define duplication
When part of the chromosome is present twice.
How does duplication occur?
Unequal crossing over in prophase I. It happens when homologous chromosomes don’t line up properly.
How many copies of ribosomal DNA and tRNA genes do humans have?
~450 copies of ribosomal DNA gene
~600 copies of tRNA genes
Many genes have multiple copies in the genome due to past duplication events.
What happens to the duplicated copy?
Since the organism doesn’t need the extra copy, the copy is inactive allowing for mutations to accumulate.
This copy is not under selective pressure, so there is nothing preventing the accumulation of mutations
Define neofunctionalization
When the duplicate gene gains a new function
Define pseudogene
AKA nonfunctionalization. Duplicate gene loses its function “false gene”
Define conservation
Duplicated gene does not change function
Define subfunctionalization
Duplicated gene does part of the function, and the original gene does other part of the function. The other half of each gene has no function
(each does half of the function)
Define specialization
Each gene does half the original function, working together. The other half of each gene does a new function.
Define gene families
Past duplications of genes and subsequent mutations create genes that have similar functions but do different things.
What is an example of a gene family?
hemoglobin gene family.
Multiple hemoglobin genes, each for a different part of development: fetal, embryo, and adult.
Define hemoglobin
Protein that carries oxygen in blood
Define inversion
When part of a chromosome is inverted - preventing chromosomes from aligning properly.
How do inversions occur?
- DNA forms a loop
- DNA break occurs
- Breaks are re-ligated incorrectly
What is the issue with inversions?
They prevent homologous chromosomes from properly aligning in prophase I. This causes the other chromosome to loop around to match, and these inverted chromosomes can still undergo crossing over (causing other issues)
What issues would crossing over after an inversion cause?
Half of each chromosome is now backwards, and some genes are duplicated while others are deleted
Define dicentric chromatid
2 centromeres caused by inversion
Define acentric chromatid
no centromeres due to inversion
Define paracentric inversion
When an inversion happens in a region that doesn’t include the centromere
Define pericentric inversion
When an inversion happens and DOES include the centromere
Define translocation
When part of one chromosome is transferred to the other. Swapping of DNA between NONHOMOLOGOUS chromosomes.
Define reciprocal translocation
Each nonhomologous chromosome breaks and connects with the opposite chromosome.
Define nonreciprocal translocation
Only one chromosome breaks and adds onto another nonhomologous chromosome.
How does translocation occur?
- 2 chromosomes become near each other
- they experience dsDNA beaks
- they are re-ligated incorrectly.
- All 4 of these chromosomes involved synapse (join together) in meiosis, influencing chromosome segregation
What type of gametes can be formed after translocation?
- Normal
- Have one of each gene
- Be missing one gene and having an extra of another
Define alternate segregation
When the gamete has one of each gene
Define adjacent segregation
When a gamete is missing one gene and has an extra of another
Define fragile sites
Thin areas of chromosomes that are more likely to break
What makes chromosomes more likely to break?
Caused by lower chromatin compaction in the region.
What is an example of a fragile site
FRA3B on chromosome 3. It often undergoes deletion and causes lung cancer.
