WEEK 7 (Gene Duplication) Flashcards
Describe Susumu Ohno’s thesis on Evolution
Products of many genes (present as only a single copy in the genome) are indispensable to the survival of members of any species during evolution -> Unique genes are not free to accumulate mutations sufficient to alter their primary function and give rise to new genes
Where are Copy Number Variations (CNVs) found?
Both coding and noncoding regions of the genome
Define Copy Number Variations (CNVs)
Copy number variation (abbreviated CNV) refers to a circumstance in which the number of copies of a specific segment of DNA varies among different individuals’ genomes. The individual variants may be short or include thousands of bases
Why are Copy Number Variations (CNVs) of major interest in genetics?
They are believed to play crucial roles in the expression of many of our individual traits, in both normal and diseased individuals
What is an Inversion?
A type of structural variation & is a type of chromosomal aberration in which a segment of a chromosome is turned around 180 degrees within a chromosome
What are the properties of Inversions?
- Does not involve a loss of genetic information but simply REARRANGES the linear gene sequence
- Requires breaks at TWO POINTS along the length of the chromosome and subsequent REINSERTION of the inverted segment
- By forming a CHROMOSOMAL LOOP prior to breakage, newly synthesised “STICKY ENDS” are brought close together and rejoined
What can the inverted segment look like?
- May be short or quite long
- May or may not include the centromere
What is the difference between Paracentric inversion and Pericentric inversion?
PARACENTRIC INVERSION = When the centromere is not part of the rearranged chromosome segment in an inverted chromosome
PERICENTRIC INVERSION = When the centromere is part of the rearranged segment in an inverted chromosome
What are the consequences of Inverted chromosomes?
Minimal impact but organisms that are HETEROZYGOUS for inversions may produce ABERRANT GAMETES that have a major impact on their offspring
What are Inversion heterozygotes?
Organisms with one inverted chromosome and one non-inverted chromosome. Two such chromosomes in meiosis can only be paired if they form an INVERSION LOOP.
What happens if only one member of a homologous pair of chromosomes has an inverted segment?
Normal linear synapsis during meiosis is not possible
What happens if crossing over happens within the inverted segment of the inversion loop?
The homologs will segregate -> Results in two normal and two inverted chromatids that are distributed into gametes
What happens if crossing over does occur within the inverted segment of the inversion loop?
Abnormal chromatids are produced
What is the difference between normal crossing over and crossing over within a paracentric inversion?
NORMAL = a single crossover between non sister chromatids produces two parental chromatids and two recombinant chromatids
PARACENTRIC INVERSION = a single crossover produces one recombinant DICENTRIC CHROMATID (two centromeres) & one recombinant ACENTRIC CHROMATID (no centromere)
What happens in meiosis in an Inverted chromosome?
During Anaphase, an ACENTRIC CHROMATID moves to one pole or the other or may be lost while a DICENTRIC CHROMATID is pulled in two directions -> Polarised movement produces AICENTRIC BRIDGES that are CYTOLOGICALLY RECOGNISABLE -> DICENTRIC CHROMATID usually breaks at some point so that part of the chromatid goes into one gamete and part into another gamete during REDUCTION DIVISIONS -> Gametes containing either recombinant chromatid are DEFICIENT in material -> During fertilisation the zygote develops ABNORMALLY
