Gene Interaction, genetic code and gen Flashcards
Incomplete dominance
blending the parental traits (making third phenotype)
polygenic type of inheritance - ex coat and eye colour
co dominance
both parental traits occur together
both alleles completely expressed
Epistasis
Multiple loci affecting two different loci
-their effects are NOT additive
Epistasis occurs:
- whenever two or more loci interact to create new phenotypes
- whenever an allele at one locus masks the effects of alleles at one or more other loci
- whenever an allele at one locus modifies the effects of alleles at one or more other loci
Epistasis is an interaction at the _____ level of organization
phenotypic
Cream dilution gene in horses
creates palomino and cremello from chestnut base colour
- cream dilution gene has two alleles Car and C
- Ccr allele is semidominant; it dilutes red to yellow in heterozygous state and red to pale cream in homozygous state
- C allele has no diluting effect on coat colour
eeCC
red coat colour
eeCCcr
palomino (gold coat with a white mane and tail)
eeCcrCcr
cremello
Mimic genes
mutations in different genes (different loci) with same phenotype
-wiry hair coat in cats (rex cats, La perm, American wirehair)
Pleiotropy
Multiple and varied effects of a single gene
-one gene affecting multiple tissues (stem cell migration)
Examples of Plieotrophy
white cats often, but not always
merle color and deafness
Lavender foal syndrome
Mutlifactorial traits
continuous scale- not categorical as mendelian traits
- independent genes at different loci
- strong environmental influence
- measured using a scale
performance trait
size (weight and height), milk yield, speed,
Diseases
OA HD Disc prolapse OC Wobbler
Polygenic traits
familial
severity scale
increased incidence with inbreeding
environmental influence
2 types of polygenic traits
threshold trait dominant gene(s) + modifying genes
Liability
probability of being affected (genotype and environment)
individual parameter
Threshold
level of liability above which all animals show the trait
population parameter
Expressivity
- all animals with the genotype show the phenotype, but to varying degrees
- refers to individual variability
- degree of variation in the severity of the defect
- variable expressivity - signs are always present
Penetrance
- polygenic trains mainly controlled by one gene
- either express the phenotype or not
- incomplete penetrance
- POPULATION VARIABILITY
- can be quantified
Phenocopies
-environment mimics the effect of a genotype
Heritability=
Vg/ (Vg+Ve)
-variance of genotype/ variance of phenotype
5 levels of genetic control
- transcription control- gene on DNA
- RNA processing control- primary transcript
- RNA transport control- mRNA
- Translation control- protein
- Post translation control - modified protein
RNA splicing occurs?
in the nucleus
Codons vs anti-codons
condons are the code on the mRNA
anti-codons are the code on the tRNA
Reading frame reads until
TAA
TAG
TGA
Mutations
=uncorrected mistakes in DNA replication which alter the DNA sequence
- somatic mutations - individual
- germ-line mutations - familiar
Types of mutations
point mutations
-substitutions- transition and transversion
-insertions
-deletions
Larger insertions and deletions
Splice mutations - mutations at the interface of axons and introns -introns remain in mRNA
Consequences of mutations
mis-sense -altered AA sequence Nonsense -preamture stop codon Silent -condon redundancy so new codon, but same AA
SNP
variation at a single position in a DNA sequence among individuals
- if more than 1% of a population does NOT carry the same nucleotide at a specific position this variation can be classified as a SNP
- if a SNP occurs within a gene, then the gene is described as having more than one allele
- SNPs can lead to variations in AA sequence
Epigenetic control
=how access to genes are regulated within the chromosome
- access to genes= acetylation of histone tails and DNA dementhylation
- murder of gene expression= methylation of DNA
X inactivation
females or individuals with two X chromosomes
- alleles on one X chromosome inactivated during embryogenesis
- each cell have different active allele
- x inactivation is random among alleles and not specific in time during embryogenesis
Imprinting
Monoallelic expression
-X inactivation in BOTH sexes
Origin of gene important - expression is parent of origin specific
Does NOT follow mender’s law of monogenic inheritance
Gene from father acts differently than gene from mother
Noncoding RNA and post-transcriptional regulation
- epigenetics and silencing of genes affects what sections of DNA are being transcribed
- area of small RNA guided gene silencing
- mRNA is for example often degraded or prevented from being translated by microRNAs
- microRNAs more stable than mRNA and sometimes cell and tissue specific
Mitochondrial inheritance
- maternal inheritance
- imparied energy production
- threshold effect- random allocation in number of mitochondria into oocytes during oogenesis
- affected males do not pass on disease
- affected or carrier females may or may not pass on defect
