Midsem test - topic 1 Flashcards
(76 cards)
Sources of genetic variation
- independent assortment at metaphase 1
- crossing over at prophase 1
- fusion with 2 gametes
Human chromosome number
46 - 22 pairs and a pair of sex chroomosomes
Telocentric
centromere at one end (<1.7 ratio)
Acrocentric
centromere off centre (>1.7 ratio)
Metacentric
centromere in middle (>7 ratio)
Telomere role
stabilise the chromosomeW
What does nucleoli contain
rRna and components of ribosomes
Nucleolar organiser
- secondary constriction
- located in different positions in different species
- contains a cluster of genes that code for rRNA
Primary constriction
centromere
Why can horse and donkeys form a mule zygote
homologous pairs dont interact during mitosis but are similar enough to make zygote
Euchromatin
- loosely packed
- rich in genes
- increased recombination frequency
Heterochromatin
- tightly packed
- less genes
- decreased recombination frequency
Common chromosome stain
Giemsa
Chromatin
- DNA associated with histones
- not uniformly distributed
Nucleosomes
DNA packed around histones
Solenoid
nucleosomes organised into coils
Proteinaceous scaffold
final arrangement of solenoid coils
Prokaryotic genome size and density
- smaller
- more dense
Why are eukaryotic genomes less dense
- genes with multiple exons are spliced in multiple different ways
Major components of eukaryotic genome
- 1.5 % exons
- Unique = introns, non coding DNA, regulatory sequences, exons
- Repetitive DNA (L1 and Alu) -includes gene families, telomeric repeats, satellite repeats and transposable elements
Dispersed gene families
- DNA sequence of genes within family that have diverged to different functions
- all proteins coded by family of homologous genes
- some have become pseudogenes
- dispersed throughout genome
- Hemoglobin = alpha and beta globin gene families have multiple different genes at different stages of life
Tandem gene families
- multiple repeats of the same gene (duplication)
- organised as tandem repeats
- often share similar functions
- examples = histones and rRNA gene in nucleolar organiser
Satellite repeats
- highly repeated tandem sequences
- heterochromatic short AT rich tandem repeats in the centromere
- can be very abundant
- short DNA sequence repeats
- vary between individuals so can be used for DNA fingerprinting and paternity tests
Microsatellites
shorter repeated DNA sequence (2-6bp) at a particular locus on the chromosome