MOLECULAR GENETICS Flashcards
Mutation types
Gene mutation and chromosomal mutation
Gene mutation
- smaller
- detected only by observing phenotype
Chromosomal mutation
- bigger mutation
- detected by looking at chromosomes with microscope
On basis of cause- spontaneous and induced mutation
Deamination
Loss of an amino group from the base
Population genetics
Describes behaviour of alleles in population by focusing on forces that can cause allele frequencies to change over time (evolution)
It is a branch of genetics which is concerned with evolutionary processes of natural selection, genetic drift, mutation, migration and non-random mating
Allele frequency
Relative frequency of an allele at a particular locus of a population, expressed as fraction or percentage.
Allele
It is a type of gene/ variant of gene
A different version of DNA sequence at specific location on a chromosome
Genotype frequency
Relative frequency of a genotype in the population
Formula = f(AA) = no. of AA individuals/ N
Where, AA = individuals possessing that genotype
N = total no. Of individuals in the sample
Factors changing the genetic structure
- mutation
- migration
- genetic drift
- non random mating
- natural selection
Hardy Weinberg equilibrium
Allele and genotype frequencies in a population tend to remain constant in absence of disturbing influences
Which would include - no mutations, no migration, random mating, no natural selection, extremely large size of population, no gene flow
Remember,
In allele frequency
p + q = 1
Where,
p = dominant allele frequency
q = recessive allele frequency
Remember,
In genotype frequency
(p+q) (p-q) = 1
(After solving)
p2 + 2pq + q2 = 1
Where,
p2 = frequency of homozygous dominant genotype
2pq = frequency of heterozygous genotype
q2 = frequency of homozygous recessive genotype
On UV exposure, which kind of mutation is caused?
Formation of thymine dimers
An example of aneuploidy
Tuner syndrome
Mutator gene
Gene, which increases frequency of mutation in other genes
Chromosomes for down syndrome in female would be
45 + XX
What is the chromosome number in trisomic individual?
2n + 1
Homologous chromosomes
Contains DNA that codes for the same trait
Genotype
Set of alleles that an individual possesses
Phenotype
Appearance of a character
Heterozygote
An individual possessing two different alleles at a locus
Homozygote
An individual possessing two same alleles at a locus
Dominant and recessive
Allele of a gene that masks or suppresses expression of alternate allele is called dominant allele
Recessive allele is masked bydominant allele
Genotype and phenotype for F2 generation in a mono hybrid cross is
Genotype = 1:2:1
Phenotype = 3:1
Genotype and phenotype for F2 generation in dihybrid cross
Genotype = 1:2:2:4:1:2:1:2:1
Phenotype = 9:3:3:1
Phenotype for F2 generation in trihybrid cross
Phenotype = 27:9:9:9:3:3:3:1
Test cross
Cross of an individual with unknown genotype, usually expressing the dominant phenotype with a homozygous recessive individual to determine the unknown genotype
Back cross
Cross between F1 genotype and either of parental genotype
Linked genes
Genes located close together on the same chromosome and belong to the same linkage group
Crossing over
During meiosis, gene occasionally switch from one homologous chromosome to another, through crossing over process, which is responsible for recombination
If genes are closely linked
No recombination
Therefore, no independent assortment
If genes are not closely linked
Recombination occurs
Therefore, there is independent assortment
Remember
Frequency of recombination measures intensity of linkage
What are the three types of DNA replication?
Semiconservative
Conservative
Dispersive
DNA replication
Takes place from 5’ to 3’ direction
Take place in the S phase of cell cycle
Occurs once per cell cycle
Purines and pyrimidines
Purines = adenine and guanine
Pyrimidines = thymine and cytosine
Telomerase
It is an RNA dependent DNA polymer is that synthesis telomeric DNA sequences
It is active in normal stem cells and most cancer cells
DNA repair mechanisms
- For direct reversal
- photoreactivation
- methyl group removal - For single strand damage
- Base excision repair (BER)
- nucleotide excision repair (NER)
- mismatch repair (MMR) - For double strand breaks
- non-homologous end joining (NHEJ)
- homology directed repair (HDR)
- micro-homology mediated end joining (MMEJ)
