Large scale chromosomal aberrations Flashcards
What are the Types of chromosome variations/mutations? Describe them.
• Relocation: o Translocation- one chromosome to another. o Inversion • Loss of genetic material: o Deletion o Missing chromosome(s) • Gain of genetic material: o Duplication o Extra chromosome(s).
What is Polyploidy? What are the different types?
• Organisms with multiple (>2) complete sets of chromosomes.
• 3 types:
o Autopolyploids: multiple sets of chromosomes from the same time and origin – mutation in chromosome number within a single species.
o Allopolyploids: multiple sets of chromosomes of different type and origin – hybridisation between related but not the same species. (At least two separate parents)
o Palaeopolyploids: organism with polyploidy ancestry but have reverted to a diploid state – deletion of duplicate gen copies etc.
What happens when Polyploidy occurs in animals?
- Not well tolerated in animal kingdom – 10% of human spontaneous abortion is due to polyploidy.
- Stable polyploids only observed in certain groups, e.g. fish and amphibians.
- Often sterile & reproduce by specialised mechanisms e.g. parthenogenesis.
- E.g. salmon & trout – tetraploids & spotted salamander.
What happens when Polyploidy occurs in plants?
- Relatively high frequency – 1 in 100,000 offspring in plants.
- Est. over 70% flowering plants have undergone polyploidisation during evolutionary history.
- Important driving force in evolution of almost all flowering plants particularly in evolution of a new species.
- Commonly consumed: coffee, potato, kiwi, banana & peanuts.
What are the Immediate effects of polyploidy?
- Increased cell and organ size.
- Greater vigour and biomass (not always).
- New phenotypes.
- New gene expression patterns.
What are the Advantages of polyploidy?
- gene redundancy:
• Masking of recessive harmful alleles by dominant wild type alleles.
• Diversification of gene function.
• Redundant copies can share different aspects of the original function.
What is polyploidy research used for?
Food security – wheat = hexaploid.
What is Non-disjunction? What causes it? What does it lead to?
- The failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division.
- Usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.
- Leads to polyploidy via meiosis – autopolyploid.
What is the Cause of age related non-disjunction?
- Human meiocytes are diplotene (Prophase I) before birth.
- Bivalents are held together by chiasmata.
- These must remain intact until meiosis resumes during menstruation. (Puberty).
- As time goes by the chance of bivalent breakdown must increase.
When does most dysjunction occur?
• Most disjunction occurs at anaphase I.
Sketch what happens in deletion? Duplication? Inversion? Translocation?
notes.
What is Partial Monosomy?
• This is where only one portion of the chromosome has one copy while the rest has two copies.
What is full monsomy? What does this cause?
- Full monosomy = aneuploidy with the presence of only one chromosome from a pair.
- Also leads to disease – Cri-du-chat.
What are the effects of a single crossover within an inversion loop in a pericentric inversion heterozygote?
- Inversion does contain centromere - therefore it can cause it to change location.
- Leads to 1 chromosome with multiple centromeres & 1 without any centromeres due to recombination.
- Meiosis leads to abnormal gametes.
What are The effects of a single crossover within an inversion loop in a paracentric inversion heterozygote?
- Inversion doesn’t contain centromere but loop forms when during pairing genes pair up with their homologues after inversion.
- This leads to two chromosomes with a centromere but an incomplete set of genetic material.
- Meiosis leads to abnormal gametes.
