Lecture 15 Chromosome abnormalities Flashcards
Define Anueploidy
This is the loss of gain of a single chromosome.
- Examples include monosomy, trisomy,
What is meant by aneuploidy
Type of chromosomal abnormality where the number of chromosomes is abnormal but not loss or gain of a complete set of chromosomes.
Explain the two main causes of Aneuploidy in humans (be specific)
1) Non disjunction of homologous chromosomes in Meiosis I
2) Non disjunction of sister chromatids in meiosis II.
Downs syndrome is which type of aneuploidy
Trisomy 21. Involves an extra copy of chromosome 21. 2n +1.
State the cause of 95 percent of downs syndrome cases
Non disjunction of homologous chromosomes in meiosis I or non disjunction of sister chromatids in meiosis II.
State the cause of 5 percent of down syndrom cases. Explain what it is.
- Robertsonian translocation accounts for 5% of all DS cases.
- ## Robertsonian translocation involves both chromosome 21 and 14.
State the type of Aneuploidy involded in turners syndrome
Monosomy ( 2n-1).
Turners syndrome results due to the loss of an X chromosome
State the karyotype for Turners syndrome
45 XO
Turners syndrome only affects which sex
Females
How many barr bodies will be visible in those affected by turners syndrome
No barr bodies visible because only one X chromosome undergoes inactivation!
State the karyotype of those affected by Klinefelters syndrome
47 XXY
Klinefelters syndrome affects which sex only
Males
How many barr bodies will be visible in klinefelters syndrome patients ( per cell)
1
Define and explain the pseudoautosomal region
- pseudoautosomal region is a conserved, homologous DNA sequences that exist on the X and Y chromosome.
- Genes in the PAR region are inherited just like any autosomal genes.
What is the function of the pseudoautosomal region
Crossing over between the X and Y chromosomes is restricted to the PAR regions.
The function of the PAR regions is that they allow X and Y chromosomes to pair and properly segregate during meiosis in males.
Explain the process of X chromosome inactivation
Females have 2 X chromsomes.
Thus, as a form of dosage compensation, ONE of the X chromsomes is inactivated. This inactivated chromosome is cytologically visible as a barr body.
How many X chromosmes undergo inactivation per cell in a female?
Per cell, just one X chromosome is inactivated, showing up as one X chromosome per barr body.
What happens to the pseudoautosomal genes during X inactivation
The PAR regions escape X inactivation.
What happens to human oocytes?
Human oocytes are paused in meiosis I for decades.
When are human oocytes produced?
Before birth in a female
What is a major cause of aneuploidy in older women
Premature loss of cohesion protein complex which holds the two homologues together up until anaphase causes formation of 2 univalents.
How many protein encoding genes are found in the mitochondrial genome. Are the genes within the mitochondrial genome smaller or larger than normal mitochondrial regions?
- Theres 13 protein encoding genes in the mitochondrial genome.
- Genes of the mt genome are usually smaller.
- Many of the genes code for proteins involved in oxidative phosphorylation.
Explain how the mitochondrial genome is inherited?
Maternal inheritance of extra nuclear mitochondria
Describe the transmission of extranuclear genomes (mitochondria and chloroplast)
Often transmitted from one generation to the next in a uniparental pattern - maternal inheritance
