Genomics Flashcards
Allelic vs non-allelic
Same gene (allelic)
Different gene (non-allelic)
Law of segregation
The two alleles from each parent separate during meiosis
Monohybrid cross
One gene which gives phenotypic ratio of 3:1
How do you find out if a phenotype is caused by a recessive/dominant mutant gene
Cross a mutant with a wild-type individual; if the mutant is dominant then F1 will contain mutants, if if it recessive then it will be seen in F2
Law of Independent assortment
Different traits assort independently of each other
Dihybrid cross
Independent assortment; 9:3:3:1
Mutation in amino acid
Results in related proteins with some differences in function
Mutation in gene regulation
Changes the amount of gene product or/and changes when and where the gene is expressed
Mutation in intron and exon
Results in proteins with different functional domains present/absent
Recessive loss of function mutation
Partial loss of gene: leaking or hypomorphic mutation
Complete loss of gene: null mutation
Haplo-sufficient mutation
One wild-type allele provides enough normal gene to produce a phenotype because mutation is recessive
Haplo-insufficient mutation
A wild-type allele cannot provide enough normal gene product to produce a phenotype because mutation is dominant
Gain of function mutation
Increase in functional gene product - Hypermorphic mutation
New function - neomorphic mutation
Allelic series
Genes in order of dominance according to the phenotypes expressed
Conditional Mutants
Mutated phenotype occurs under certain environments
Restrictive condition: mutant phenotype
Permissive condition: wild-type phenotype
Penetrance
The proportion of individuals of a specific genotype that exhibit the corresponding phenotype
Incomplete penetrance: not everyone displays the mutant
Lethal alleles
Dominant lethal alleles
Homozygous mutant
Offspring ratio = 2:1
Recessive lethal alleles
F1 intercross of heterozygotes - ¼ of offspring will die
Offspring ratio = 1
Lethal alleles result in altered 3:1 ratios = dominant (2:1) or recessive (3:0)
Pleiotropic
A single gene with more than one phenotype
The complementation test
Determines whether recessive mutants are from the same gene or two different genes
Two homozygous mutants with the same phenotype are mated
If the F1 is the wild-type, the two mutations complement each other and represent two different genes
If the F1 is a mutant, the two mutations fail to complement and represent two different alleles of the same gene.
Gene interactions
Complementary gene interaction: the activity of both genes is needed for the final phenotype - 9:7
Duplicate gene interaction: either gene can carry out the biological process (redundancy) - 15:1
Dominant gene interaction: two genes with the same phenotype interact additively - 9:6:1
Epistasis
One gene masks the phenotype of another
Recessive epistasis: the recessive genotype of one gene blocks the phenotype controlled by another gene - 9:3:4 ratio
Mitosis
somatic cells - chromosomes replicate and divide, chromosome number is maintained
Meiosis
Germline cells - chromosomes replicate and undergo 2 rounds of division, chromosome number is halved
The chromosome theory of Inheritance
Sutton & Boveri (1902): The behaviour of chromosomes during meiosis can explain why genes are inherited according to Mendel’s Laws