Cell cycle & genetics Flashcards
What are cells in the cell cycle known as?
Labile cells - cells that multiply constantly throughout life.
What are cells that never enter the cell cycle known as?
Permanent cells
What are cells that are not in the cell cycle, but can enter, known as?
Stable cells
How many divisions take place during mitosis?
1
What are the stages of mitosis?
Interphase Prophase Prometaphase Metaphase Anaphase Telophase
What happens during prophase?
Chromatin condenses into chromosomes. Two centrosomes (microtubule organising centre of cell) begin recruiting microtubules and move to opposite poles of the nucleus.
What happens during prometaphase?
The nuclear membrane dissolves.
Microtubules invade the nuclear space.
Cell no longer has nucleus.
What happens during Metaphase?
Microtubules attach to kinetochores and chromosomes begin to line up in the middle of the cell.
What happens during Anaphase?
The proteins that bind the sister chromatids are cloven and they separate.
Then microtubules shorten as spindle fibres contract to pull apart the chromatids towards opposite poles.
The chromatids reach the opposite ends and are now known again as chromosomes.
What happens during Telophase?
The nuclear membrane reforms around the genetic material.
The chromosomes are unfolded back into chromatin.
What is cytokinesis?
Cell organelle become evenly distributed around each nucleus.
The cellular membrane pinches off between the separated nuclei, forming two new daughter cells.
What is a primordial (undifferentiated) germ cell?
An embryonic precursor of the gametes. They go on to produce spermatogonia (mature sperm) in males, and oogonia (immature reproductive cell) in females.
What is an oocyte?
A cell in an ovary which may undergo meiotic division to form an ovum.
Oogonium give rise to primary oocytes by mitosis.
What is spermatogenesis?
Spermatogonia undergo spermatogenesis to form mature spermatozoa in tubules of testes.
How many mitotic divisions do PGCs undergo to produce oogonia?
A) 15
B) 45
C) 30
D) 150
C) 30
At ovulation, how many divisions of meiosis does the cell complete?
Only 1 division takes place (Meiosis I) at ovulation.
Meiosis II only occurs if fertilisation occurs.
How many eggs are produced by the oocyte?
During meiosis I, the oocyte divides to produce 1 polar body, and secondary oocyte. During meiosis II, the cells divide to produce an ovum and a second polar body.
This is due to unequal division of the cytoplasm.
Define Gonadal Mosaicism.
Gonadal mosaicism is a special form of mosaicism, where some gametes (sperm or oocytes) carry a mutation, but the rest are normal. The cause is usually a mutation that occurred in an early stem cell that gave rise to all or part of the gametes.
Result of Gonadal Mosaicism
The foetus may inherit a genetic disease, whilst their parents are healthy.
What are the 3 ‘types’ of disease?
Genetic
Multifactorial
Enviromental
What does this define?:
“any chromosome other than sex chromosomes”
An autosome
Define Allelic Heterogeneity
Different mutations within the same gene result in the same clinical condition.
Define consanguinity
A reproductive union between two relatives.
What does this define?:
“Homozygosity by descent (inheritance of same altered allele through 2 branches of the same family)
Auto-zygosity
Autosomal recessive diseases…
manifest in the homozygous state (2 of affected allele)
What are 3 features of autosomal recessive conditions?
1) Male and female equal proportions
2) Affected in single generation
3) Parents related increases chance
An example of an AR condition.
Cystic Fibrosis
How many mutations are known to cause CF?
Over 1,000
Autosomal Dominant diseases…
manifest in the heterozygous state (only 1 allele needed)
What are 4 features of AD conditions?
1) Male & female equal proportions
2) affected individuals in multiple generations
3) Transmission by both sexes to both sexes
4) only mode of inheritance with male to male transmission
Define Penetrance
The percentage of individuals with a specific genotype who show expected phenotype.
What is expressivity?
The range of phenotypes expressed by a specific phenotype.
Explain a recurrence risk.
The recurrence risk is 50% for transmission of a mutation, but whether it will affect the person depends on the penetrance/expression.
For example, with Treacher Collins syndrome, there can be variable expression.
What is a de novo mutation?
An alteration in a gene that is present for the first time in one family member, as a result of a mutation in germ cell (or in the fertilized egg itself).
Give the term that explains when a genetic disorder affects successive generations earlier/more severely, due to the expansion of unstable triple repeat sequences.
Anticipation
What is somatic mosaicism?
Somatic mosaicism is the accumulation of mutations in DNA sequence or copy number in cellular genomes after fertilization (typically in the form of copy number variations, single nucleotide mutations, new retrotransposon insertions).
What does this define?:
“Any cell of a living organism other than a reproductive cell”.
A somatic cell
Explain what is meant by late-onset.
The condition does not manifest at birth, it develops as the individual becomes adult.
An example is hypertrophic cardiomyopathy.
What does sex-limited mean?
When a condition inherited in AD pattern seems to affect one sex more than the other.
For example, breast cancer caused by a mutation of the BRCA1/2 gene.
What is predictive testing?
Testing for a condition in a pre-symptomatic individual to predict their chance of developing a condition.
Describe what is meant by a translocation.
Parts of the chromosomes have swapped over.
Name and explain the 2 different types of translocation.
Reciprocal translocation is the mutual exchange of fragments between two broken chromosomes.
Robertsonian translocation is the fusion of the whole long arms of two acrocentric chromosomes.
What is it called when a piece of chromosome breaks off, rotates 180 degrees, and re-joins?
An inversion
Explain the 2 different types of inversions.
Paracentric- centromere is involved
Pericentric- centromere is not involved
In a …………. part of the chromosomes is removed.
deletion
Explain interstitial deletion.
This is where there are 2 breaks in the chromosome, and the broken ends fuse together, leaving out the middle deleted segment.
Explain terminal deletion.
This is the loss of an end of a chromosome.
What us it called when a segment of chromosome is duplicated in the same order?
A tandem duplication.
How many genes do humans have?
22,000
Each chromosome has a long arm (q) and a short arm (?)
p - petit = short
What happens during interphase G1?
Rapid growth
Normal metabolic function
New organelles produced
Protein synthesis of proteins involved in spindle formation
What happens during S phase of interphase?
DNA doubles through DNA replication.
Histone proteins double through protein synthesis.
Centrosome replication.
What happens during interphase G2?
Chromosomes condense and become visible.
Energy stores accumulate.
Mitochondria and centrioles double.
Where does meiosis occur?
only in gametes
Why is there genetic diversity after meiosis?
Crossing over.
Random recombination of genetic material.
How many cell divisions are there in meiosis?
2
How many daughter cells are produced?
4
What are the daughter cells known as and why?
Haploid- they contain half the number of chromosomes as the parent cell.
They are genetically distinct from each other and the parent cell.
What happens during meiosis 1?
Chromosome number halved.
Genetic diversity:
P1- crossing over between non-sister chromatids
M1- random assortment occurs on metaphase plate
What happens during meiosis 2?
sister chromatids separate.
Haploid cells produced.
What is the first stage of gametogenesis?
Proliferation of primordial germ cells by mitosis.
What is the process of gametogenesis in males?
PGC -> MANY MITOSES -> SPERMATOGONIA
Mitosis begins during puberty and continues throughout life.
Cytoplasm divides evenly.
After meiosis 2 -> 4 equal size gametes.
Millions of mature sperm continually produced.
How long does gametogenesis take in males?
60-65 days.
What is the process of gametogenesis in females?
PGC -> 30 MITOSES -> OOGONIA
Oogonia enter P1 of meiosis 1 by 8th month of intrauterine life.
Process suspended.
Cells enter ovulation 10-50 years later.
Cytoplasm divides unequally forming 1 egg and 3 polar bodies.
M1 is completed at ovulation.
M2 is only completed if fertilisation occurs.
