IMMS Flashcards
Where is DNA found? What is the structure of DNA?
Nucleus and mitochondria. Double helix with strands in opposite directions. Complementary base pairs between strands. A-T = 2 bonds, C-G = 3 bonds
How is DNA packaged into a chromosome?
DNA coils around histones to form nucleosomes, coils again into supercoils + again into chromosomes
How many chromosomes are there to each cell? What are the two chromosome arms?
46 chromosomes (23 pairs). Long arm (q) + short arm (p(etite)) separated by centromere
Which two dyes are used to stain chromosomes?
- Giemsa = G banding - Quinacrine = Q banding, each band = 6-8 million base pairs
What is the purpose of mitosis?
- To produce 2 genetically identical daughter cells - For growth + to replace dead cells
What stage must a cell be in for mitosis to start? What happens in the synthesis stage for the cell cycle?
Cell must be in interphase. S phase = DNA and centrosome replication

What happens in the first stage of mitosis? Remember IPPMAT
Prophase: - Chromatin condenses into chromosomes - Centrosomes nucleate microtubules + move to opposite poles of nucleus

What happens in the second stage of mitosis?
Prometaphase. - Nuclear membrane breaks down - Spindle fibres begin to form

What are cells called that are permanently in the cell cycle? How about cells that never enter the cell cycle?
Permanently in = labiles. Never in = myocytes
What is the third stage of mitosis?
Metaphase. - Chromosomes line up along equatorial plane

What is the fourth stage of mitosis?
Anaphase. - Sister chromatids separate + pushed to opposite poles of cell

What is the last stage of mitosis?
Telophase. - Nuclear membranes reform - Chromosomes unfold into chromatin - Cytokinesis begins

What is the clinical relevance of studying cells undergoing mitosis?
- Can detect chromosomal abnormalities - Can categorise tumours as benign or malignant - Can grade malignant tumours - lots of mitosis = high grade
Which drugs can be used to disrupt mitosis?
To break mitotic spindle: - Taxol -Vinca alkaloids, e.g. vinblastine To break spindle poles: - Ispinesib To stop anaphase: - Colchicine-like drugs
What is meiosis? How is different to mitosis?
Only occurs in gametes, has 2 cell divisions to create 4 genetically varied haploid daughter cells. It is also not a cycle
What is crossing over? Where in meiosis does it take place?
Crossing over = sorting genes independently. Takes place in Prophase 1. - 1: Interphase G1, Interphase S, Prophase 1, Metaphase 1, Anaphase 1, Telophase 1 - 2: Prophase 2, Metaphase 2, Anaphase 2, Telophase 2, Cytokinesis

What is the difference between sperm and egg production?
Sperm: cytoplasm divides evenly, 4 equal gametes after meiosis 2 Egg: cytoplasm divided unequally to give 1 egg and 3 polar bodies (that apoptose). Meiosis completed at ovulation, meiosis 2 only completed if fertilisation occurs
What is non-disjunction?
The failure of chromosome pairs to separate in meiosis 1 or sister chromatids to separate properly in meiosis 2, e.g. Down syndrome = extra chromosome on 21
What is gonadal mosaicism?
All or part of parental germline is affected by disease mutation, but the parental somatic cells are not affected. Parent = healthy, foetus may have genetic disease. Risk increases with parent age
What are the 3 categories of disease causation?
- Genetic, e.g. Down’s syndrome - Multifactorial, e.g. Spina bifida - Environmental, e.g. scurvy from poor diet
What do phenotype and genotype mean?
- Genotype = genetic constitution of an individual - Phenotype = appearance of an individual = result of genotype + environment
What do the terms allele and polymorphism mean?
- Allele = one of several forms of a gene - Polymorphism = frequent hereditary variations at a locus
What do homozygous, heterozygous and hemizygous mean?
- Homozygous = both alleles the same at a locus - Heterozygous = alleles different at a locus - Hemizygous = only one allele refers to a locus on an X chromosome in a male
What are the 3 categories of genetic disease?
- Chromosomal - Mendelian, e.g. autosomal dominant/recessive, X-linked - Non-traditional, e.g. mitochondrial, imprinting (one allele active, other inactive) + mosaicism (error in cell division, same cells have different genetic makeup)
























































































