Lecture 11 Flashcards
Labile cells
Multiply throughout life,
Ex) epithelial cells, cells of skin, GIT
Stable cdlls
Quiescent, can divide if stimulated
Ex) liver cells
Permanent cells
Doesnt divide, permanently in G0 phase.
Ex) neuron, cardiac muscle cells
G1>S checkpoint
Growth factor stimualte disivison.
Protein such as p53 and Rb check for DNA damage before cell exits G1 phase.
Role of p53 in cell cycle
If DNA damage, cell cycle arrest or activation of G1-S checkpoint! And activates DNA repair systems.
If damage is extensive, cause apoptosis.
When is chromosome maximally visible?
Metaphase (karyotype)
Events in prophase
Nuclear envelop dissolves
Mitotic spindle forms and chromosome starts binding to spindle.
Chromosome starts condensing and become visible
What happens when mitotic non-disjunction happen during embryogenesis
Failing of separation of sister chrimatid results in aneuploidy in daughter cell, resulting in mosaic in fetus.
Difference between mixed somatic/germline mosaic and confird germline mosaic
Mixed means both somatic and germline cells are mosaic, but confined means all somatic cells have one genotype, while only cells of gametes are something else, which leads to high risk of having children with genetic disorder.
What is exchange of short fragment of genetic material between homologous chromosomes? And when does it happen?
Homologous recombination or crossing over during prophase I
What is the name for crossing over regions
Chiasmas
At which stage of meiosis cause genetic diversity?
Prophase 1 (crossover) Anaphase 1 (random segregation of homologous chromosomes
In nondisjunction meiosis 1, what does not separate?
Homologous chromosomes do not separate
In nondisjunction meiosis II, what does not separate?
sister chromatid does not separate
What happens to chromosome number of gametes when nondisjunction occur in meiosis 1?
All abnormal gametes(all aneuploidy)
2 trisomy and 2 monosomy
What happens to chromosome number of gametes when nondisjunction occur in meiosis 2?
2 abnormal gametes with aneuploidy and 2 normal gametes
1 trisomy and 1 monosomy
What is trisomy?
3copies of specific chromosome
Monosomy
1 copy of specific chromosome (only Monosomy X is compatible with life)
How can we differentiate between nondisjuction during meiosis I and meiosis II?
Using marker analysis
A chromosome has markers A and B on each homologous chromosome
If a child has both marker A and B, then nondisjunction in meiosis I happened
If a child has duplicate of marker A, then nondisjunction in meiosis II happened.
What happens if sex chromosome nondisjunction meiosis I occur in male?
2 sperms wouldn’t have sex chromosome at all
and 2 sperms would have x and y chromosomes each.
As a result when these sperms fertilize with ovum, first 2 sperm cells would have single X chromosome , which is Turner syndrome (45,X).
Last 2 sperms would have XXY chromosomes, which is klinefelter syndrome (47, XXY).
What is maternal uniparental disomy?
Both copies are derived from mom
What happens if sex chromosome nondisjunction meiosis II occur in male?
After fertilization, 2 sperms will end up with Turner syndrome (45,X).
1 sperm with 47,XXY
1 sperm with 47, XXX
What happens if sex chromosome nondisjunction meiosis I occur in female?
2 ovum with 47,XXX
2 ovum with 45,X
What happens if sex chromosome nondisjunction meiosis I occur in female?
1 ovum with 47,XXX
1 ovum with 45, X
2 normal gametes
Comparision of male and female gametogenesis (3)
- Male produce four sperm cells per round while female produce 1 egg and 3 polar bodies per round
- Spermatogenesis begin at puberty while oogenesis begin at early embryonic life (primary oocyte arrested in prophase I of meiosis at birth)
- gamete production for male :100-200 million per ejaculation
1 ovum per menstrual cycle - Females have completed all mitotic division of cell by birth while male continue their mitotic division of cell until puberty
What does ovulation mean in terms of meiosis?
completion of meiosis 1
When is meiosis II completed for female?
only after fertilization
Defects if maternal or paternal age is increased (2)
- Higher risk for non-disjunction in a female greater than 35 years, resulting in higher risk of trisomy in fetus
- Higher the paternal age, greater is the risk of development of new dominant single gene mutations (error during replication)
Where does mitosis and meiosis take place?
Mitosis in all dividing somatic cells and during embryogenesis &initial stage of gametogenesis
Meiosis in germline cells during gametogenesis
