Chromosomes and Development Flashcards
What is the largest cause of congenital anomalies?
Mendelian disorders
2 points that are susceptible to errors in mitosis
DNA replication
Chromosome segregation
2 essential features of meiosis
Chromosomal pairing
DNA exchange
When does a cell go from diploid to haploid
At the end of meiosis 1
Homologous pairs separate
Non-disjunction
In meiosis (1 or 2)
Erros in chromosome segregation
Whole chromosome loss or gain
What factor is a risk for non-disjunction?
Mother’s age
Increases as she ages
When is meiosis halted in oogenesis?
At the end of MI (end of embryogenesis)
During MII (until just before ovulation)
Resumes after ovulation is triggered by fertilization
When does the oocyte number peak?
Embryonic week 20
Aneuploidy
Gain or loss of an entire chromosome
How to identify:
- Aneuploidy
- Insertions or deletions
- Copy number variants
- Whole chromosome
- Cytogenic resolution
- Submicroscopic (chromosome microarray)
3 examples of structural variants
Translocations
Inversions
Complex rearrangements
2 types of translocations and what they mean
Reciprocal (exchange of broken segments)
Robertsonian (fusion of 2 acrocentric chromosomes near the centromere)
Where does the problem with translocations occur?
If they occur in germ cells they can cause unbalanced genetic information in the progeny
What are the 5 acrocentric chromosomes?
13, 14, 15, 21, 22
Robertsonian translocations are
1. balanced
2. unbalanced
when you have how many chromosomes?
- 45
2. 46
Turner syndrome
Missing an X chromosome
Infertility, short stature, cardiac problems, but normal intelligence
Chromosomal microarray
Gain or loss of 0.25-10Mb (or more) of a genome
Take patient DNA, label with probe on slide that has reference DNA
DNA is either labelled with a different colour (measure the balance) or the same colour (measure the brightness)
Williams Syndrome
Deletion in chromosome 7
Intellectual disability, short stature, different behaviour and appearance
