What is the end replication problem?
through multiple generations, strands will get shorter
What is the solution to the end replication problem?
telomerase
What are centromeres?
- Protein complexes that bind to microtubules and are required during cell division
- They are the constricted region joining sister chromatids
- site of kinetochores
- repetitive SNA sequences- satellite DNA
Hererochromatin vs Euchromatin
- Heterochromatins has a condensed structure and silenced genes
- Euchromatin has an open structure and active genes
Describe the structure of chromatin.
- formed of DNA packaged histones
- histones have a positive charge, DNA negative
- 146 bp DNA wrapped around core of 8 histones= nucleosome
- further wrapping of nucleosomes
- form solenoid structure
By what factor is DNA condensed by at metaphase?
10,000
What is the purpose of packaging DNA?
- negatively charged DNA neutralised by positive charged histone proteins
- DNA takes up less space
- Inactive DNA can be folded into inaccessible locations until required
What is colchine?
- a microtubule inhibitor
- it enriches the population of cells that are visible
Metacentric
p length= q length
Submetacentric
p length< q length
acrocentric
p length «< q length
What does FISH stand for?
Fluorescent in situ hybridisation
What types of FISH probes are there?
- unique sequence probes
- centromeric probes (useful for determining chromosome number)
- telomeric probes (detecting subtelomeric rearrangements, often present in children wit unexplained mental retardation)
- whole chromosome probes (cocktail of probes, used with different dyes, spectral karyotype, detecting translocation and rearrangements)
What is meiosis?
- cell division in germ cells
- diploid cells (in ovaries and testes) divide to form haploid cells)
- chromosomes are passed on as re-arranged (recombinant) copies which creates genetic diversity
What is a defining event in sexual reproduction?
recombination between homologues
What are the 2 forms of gametogenesis?
- oogenesis= process of egg formation
- spermatogenesis= process of sperm formation
Why is there a greater chance of mutation in sperm than in eggs?
they go through more cell divisions
How many sperm and eggs are produced in each cycle of gametogenesis?
- 4 sperm
- 1 egg + 3 polar bodies
Describe fertilisation.
- two haploid cells form 1 diploid cell which develops into an embryo
- whether sperm contains an X or Y chromosome determines if the embryo is female or male
- embryo contains an assortment of genes from each original parent- more genetic diversity
What is maternal inheritance?
mitochondria (and their DNA) come only from the mother via the egg
When does X inactivation occur?
- In the zygote both X chromosomes are active
- In the early embryo random inactivation of one X occurs
What are 2 tandemly repeated DNA extragenic sequences?
- satellite DNA
- microsatellite DNA
What are 2 highly repeated interspersed DNA extragenic sequences?
-SINEs (short interspersed nuclear elements)
LINEs (long interspersed nuclear elements)