Higher Eukaryotic Chromosomes Flashcards
What is meant by karyotype?
The number and visual appearance of the chromosomes in the cell nuclei
True or False:
The number of chromosome is indicative of species’ complexity
False. Number of chromosome is uninformative. Think of it as two books with the same content but different number of chapters
List the possible identifiers of a chromosome (3)
- Size
- Centromere position
- G-banding
Explain how centromere position can be a possible identifier (3)
A chromosome can have its centromere in several different positions:
- Acrocentric -> close to one end
- Submetacentric -> off-centre
- Metacentric -> centrally located
Explain what would be seen in Giemsa Staining
Giemsa staining is the staining of nucleic acids.
A-T will be seen as dark bands (gene poor)
G-C will be seen as light bands (gene rich)
List the possible types of abnormalities
- Numerical, change in gene number
- Structural, change in gene position
What is polyploidy?
The addition of one or more sets of chromosomes.
Ex. triploidy (3n = 69)
Humans too sensitive and often miscarriage occurs
What is aneuploidy?
The loss or gain of one or more chromosomes
What are possible structural changes that can occur?
- Deletion
- Duplication
- Inversion
- Translocation
What are the causes of each abnormality?
- Aneuploidy, non-disjunction
- Structural Abnormalities, DNA breakages or non-allelic homologous recombination
What is meant by inversion?
A chromosomal mutation consisting of the removal of a chromosome segment, its rotation through 180 degrees, and its reinsertion in the same location
What are the types of inversions? (2)
- Paracentric - inversions flanking the centromere
- Pericentric - inversions encompassing the centromere
What is meant by translocation?
The relocation of a chromosomal segment to a different position in the genome
Explain the pairing and segregation of reciprocal translocation
Chromosomes form a cross-shaped pairing
1. Alternate (T1 + T2) or (N1 + N2): complete and viable
- Adjacent (T1 + N2) or (N1 + T2): duplication and deletion of segements
What is Robertsonian Translocation?
Centric fusion of acrocentric centromeres
What is meant by synteny?
A situation in which genes are arranged in similar blocks in different species
Explain the Eutherian Karyotype
The theory that chromosomes from different species have shared ancestry. The genome remains the same but is split and rearranged in different blocks
What is the c-value paradox?
Genome size does not reflect complexity of an organism
If genome size does not correlate to complexity, what does it correlate to?
Amount of DNA derived from transposable elements.
Genes are relatively constant components of genomes. Therefore the additional DNA in larger genomes are due to repeated DNA sequences
What is the Cot Renaturation Curve used for?
It measures how much repetitive DNA is in a DNA sample using the principles of DNA reassociation kinetics
What is the principles of DNA reassociation kinetics?
the rate at which a particular sequence reassociates is proportional to the number of times it is found in the genome
Give examples of unique components of the genome (3)
- non-coding intervening sequences
- non-coding control sequences (promoters, enhancers etc)
- CpG islands
Where are genes most often found?
Genes are unevenly distributed in the chromosome. Genes are more concentrated in areas of high G-C content
What types of mutations can a duplicated gene acquire? (3)
- Inactivating mutation: inactivated paralog is known as pseudogene (invisible to nat. sel.)
- Alter activity of gene (neofunctionalisation)
- Function divided between dupe, complement one another. Subfunctionalisation
How is haemoglobin an example of repetitive sequences?
Genes for adult alpha chain in Chr 16 has a cluster of 5 repeated genes and beta chain in Chr 11 has cluster of 6 genes. However, gene families produce different proteins
Each cluster has pseudogenes
Which types of transposable elements appear most often in the genome? (2)
Retrotransposons called Long Interspersed Elements (LINEs) and Short Interspersed Elements (SINEs)
How are LINEs and SINEs so abundant?
SINEs and LINEs have integrated using reverse transcription
The DNA sequence transposes via RNA intermediate via copy and paste mechanism
LINEs are autonomous and encode own reverse transcriptase. SINEs use RTase produced by LINE
What are VNTRs?
Short sequences repeated over and over in tandem
Variable Number Tandem Repeats
What are the types of VNTR? (3)
Largest: Satellite (>100 bp) located in centromere area
Minisatellite (15-100bp)
Smallest: Microsatellite (<15bp). Located in telomere area
What are the causes of VNTRs? (3)
- Due to similarity, when lined up = unequal crossover
- DNA replication slippage (re-replication or lost of replication)
- DNA repair
