Flashcards in Mitosis and Meiosis Deck (44):
What is the smallest subunit of chromatin called?
Nucleosome (DNA wrapped around a bundle of 8 histone proteins).
What happens in prometaphase?
The nuclear envelope disintegrates and kinetochores (proteins on the centromere that form the point of attachment of microtubules) are formed, and the chromosomes attach themselves to the mitotic spindle.
What is a karyotype?
How the chromosomes look when they are condensed (around a non-histone protein chromosomal scaffold) and become visible in prophase (they are arranged in order of size and position of centromere). Can be used to detect aneuploidy e.g trisomy 21 (which causes Downs syndrome).
When you burst the nucleus at prophase some of the chromosomes overlap so you need to look at a big sample.
What is aneuploidy?
An abnormal number of chromosomes e.g monosomy, trisomy. It is caused by nondisjunction.
What is G0?
The resting phase where the cell will not divide. Epithelial cells are in G0 all the time, until you cut yourself where they move to G1.
What is G1?
G1 is Growth Phase 1, which occurs just after mitosis in the cell cycle and is the first part of interphase. The cell increases in size (so it is not cleavage when it divides) and replaces organelles lost in the previous division.
What is S1?
S1 is Synthesis Phase 1, where the cell replicates all the DNA in its nucleus.
What is G2?
G2 is Growth Phase 2, just before mitosis, where the cell checks that its DNA has been replicated correctly, and the centrosomes are replicated.
What is translocation?
Non-homologous chromosomes break and interchange portions. The person may be asymptomatic if no genetic material is lost, but their gametes will have incorrect amounts of genetic material.
What is cytokinesis?
Microfilaments constrict the cytoplasm perpendicular to the spindle.
Which is the p arm of the chromosome and which is the q arm?
The p arm is the top, the q arm is the bottom.
What is it called when the q arm is much longer than the p arm?
Why would you look at the banding pattern of the chromosomes?
To check they haven't been translocated, truncated, elongated, inverted, isochromosomes.
What makes the banding pattern of chromosomes?
The dark and light bands of heterochromatin and euchromatin.
How can chromosomes be abnormally altered during cell division (changing the banding pattern)?
1) Sections can be deleted - truncation.
2) Sections duplicated - elongation.
3) Portions inverted.
5) Isochromosomes formed.
How are isochromosomes formed?
The centromere of an acrocentric chromosome with sister chromatids is transversely split. The two q arms bind together and the two p arms bind together to create two chromosomes, each with identical length sections and identical genes above and below the centromere.
What is a polymorphism?
When there are more than two different types of alleles.
Why is an X-linked recessive allele always expressed in males?
Males are hemizygous (have only one X chromosome).
What does a triangle mean, and what does a triangle with a line through it mean?
Triangle = miscarriage.
Triangle with line through = abortion.
What does a square with a P in it mean?
What does a circle with a line through and SB underneath mean?
What does a diamond mean?
Offspring of unknown sex.
What does square brackets around the shape mean?
What does a circle with a black dot in the middle mean?
Female carrier of X-linked recessive allele.
What is the process that forms tetrads in Prophase 1 of meiosis?
What is the difference between a somatic and germ-line mutation?
Somatic mutations occur after meiosis (gametogenesis) and so only affect the tissues surrounding the area of the mutation, and so only affect the individual and not their offspring. Conditions caused by somatic mutations tend to be late-onset and unilateral.
Germ-line mutations occur during meiosis in gametogenesis and so affect all the cells in an individual (including germ cells, so the mutation is passed on through inheritance). The arising condition tends to be early-onset and bilateral.
(With cancer, a germ-line mutation can give someone a predisposition, then sporadic somatic mutations will allow the cancer to develop.)
What is the mutation called where one nucleotide in the allele is replaced?
Single nucleotide polymorphism (SNP).
What is the mutation called where a difference in the nucleotide sequence causes one amino acid to be substituted for another?
What is the mutation called where a change in the nucleotide sequence changes a codon to a stop codon, so the protein is truncated?
What is the mutation called where a base is added or deleted, so there is an unnatural reading frame from the point of the mutation to the end of the gene?
What is the mutation called where the number of repeats in a repeated sequence of bases (short tandem repeats/hyper-variable region) gets unfaithfully replicated?
What is a restriction fragment length polymorphism (RFLP)?
Defined by the existence of alternative alleles associated with restriction fragments that differ in size from each other. Detected by breaking DNA up using a restriction endonuclease enzyme, then using gel electrophoresis to split the DNA up into a banding pattern.
Some alleles won't have restriction site present.
What is a microsatellite?
A short tandem repeat (highly polymorphic).
What is involved in the Polymerase Chain Reaction (thermal cycling)?
Start with a mixture containing target DNA, primers, buffers, DNA polymerase, and free nucleotides.
Heat to 95 degrees to denature DNA.
Cool to 55 degrees to allow primers to bind (anneal).
Heat to 70 degrees to activate DNA polymerase.
Is crossing over more or less likely when the linked genes are further apart?
More likely - more likely for recombinants to form.
What is the Hardy-Weinberg principle?
p2 + 2pq + q2 = 1
To calculate the allele frequency of an autosomnal recessive allele.
What is necessary in the population for evolution to happen and the Hardy-Weinberg principle to apply?
1) Limited population size.
4) Selective mating.
5) Natural selection.
What is the Founder Effect?
When a small group of individuals with an allele frequency that is not representative of the original gene pool is isolated and develops a new population. e.g high incidence of familial colon cancer in Finland due to the original settlers.
There will be genetic drift when the isolated population is small.
Also, a natural disaster like an earthquake will lead to a reduction in genetic diversity.
What is genetic drift?
Changes in allele frequency due to random chance.
What is consanguinity?
Marriages within close family members.
What is heterozygote advantage?
When the recessive allele persists within the gene pool because heterozygote individuals have an advantage in relation to a selection pressure.
e.g Vitamin K deficiency in rats and warfarin resistance.
Malaria resistance in people with sickle cell trait.
During which stages does the centres one divide?
Begins in G1, completes in G2.
What is the function of microtubules? (Part of the cytoskeleton)
They are involved in cell movements e.g cytokinesis, mitosis and vesicular transport