Chromosomal Mutations Flashcards
Chromosomal Mutations
- Variation in the structure
- Number of chromosomes
Chromosomic mutations
- Deletion
- Duplication
- Inversion
- Translocation
Deletion
Consists of a deletion of a part of a chromosome
2 types of deletions
- Terminal deletion: consists of a single break in the terminal part of a chromosome
- Interstitial deletion: consists of the breakage of the chromosome in the middle of one arm: chromosome without centromere is generated and so is lost during replication
Cri-di-chat syndrome
Deletion of chromosome 5
Dangerous consequence of deletion
Loss of heterozygosity: copy of genes reduced from 2 to 1 which leads to protein insufficiency
Duplication
Duplicates a region of the chromosome
How is duplication caused?
Due to crossing over in which there is unequal pairing of repeated regions due to misalignment
Can duplication be advantageous?
Yes and it can be fixed and favoured in the genome i.e. alpha and beta globin of hemoglobin
A dangerous consequence of duplication
Certain regions are overexpressed
Inversion
Occurs when a part of a chromosome breaks and is rejoined with a rotation of 180 degrees of the sequence
Paracentric inversion
Does not involve the centromere
Pericentric inversion
Includes the inverted region and the centromere
Where does the issue arise in inversion?
When there is a pairing of homologous chromosomes: the pairing occurs in a loop to have the gene’s sequences matching
Acentric chromosome
No centromere
What happens to acentric chromosomes?
Lost due to the lack of centromere
Dangerous consequence of inversion
Silencing, some genes may be replaced in different chromatin context
Translocation
The breakage within a chromosome, after which the genetic material is joined in a different chromosome
Direct translocation
Part of a chromosome is directly translocated into another one
Reciprocal translocation
An exchange of genetic material, meaning both chromosomes are involved in translocating their genetic material from one another
What does translocation not lead to?
To the loss of how DNA is transcribed
What is nonreciprocal intrachromosomal translocation?
Goes from the region of one chromosome into another region of the same chromosome
What is nonreciprocal interchromosomal translocation?
A region of a chromosome moved into another chromosome
What is reciprocal interchromosomal translocation?
exchange of genetic material between different chromosomes
What does the short arm consist of?
Satellite DNA= non-coding repetitive sequences + genes for RNA
Metacentric
When the centromere is located exactly in the middle
Acrocentric
When the centromere is moved towards the ends of the chromosome
When can Robertsonian translocation occur?
When the centromere is moved towards the ends of the chromosome
5 acrocentric chromosomes in our genome
13
14
15
21
22
Down syndrome
Due to trisomy 21 or Robertsonian translocation between chromosomes 14 and 21
Reciprocal translocation between acrocentric chromosomes
could form one chromosome with 2 long arms and a centromere and 2 short arms which is then lost
Nullisomic
Lack of a pair of homologous chromosomes of one chromosome LETHAL
Monosomy
one of the 2 homologous chromosome is missing LETHAL
Double monosomy
two chromosomes are missing, but in 2 different pairs of homologus chromosomes
Trisomy
one extra chromosome
only non-lethal is trisomy 21
Tetrasomy
2 extra homologous chromosomes
Double tetrasomy
2 extra chromosomes on 2 different homologous chromosomes
Triploidy
A condition which there are 3 copies of chromosomes [XXX or YYY] LETHAL
Why are sex chromosome mutations more likely to be compatible with life?
Because of chromosome X inactivation
Turner Syndrome
Women who lack one X chromosome
Human aneuploidy
abnormally high number of chromosomes
Anaphase lagging
One chromosome is left behind during separation and is lost during cell division
Non-disjunction in meiosis I
All of the 4 daughter cells will be chromosomally abnormal
Non-disjunction in meiosis II
2 will be normal and 2 daughter cells will present aneuploidy
