extension to mandelian inheritance Flashcards
complete dominance
one allele completely masks the other gene 3:1 ratio
incomplete dominance
one allele does not completely mask the other, 2 of the same allele is needed. the heterozygous is a blend of the two.
co-dominance
both alleles are present in phenotype - neither is dominant ratio = 1:2:1
ABO (co-dominance)
A and B are dominant, O is recessive. glycosyl-transferase enzyme adds a sugar group. it can create the A or B antigen. if both transferases are active both antigens are present
overdominance
the heterozygote is better for survival/reproduction than either homozygote
sickle cell anemia
homozygous dominant - unaffected but non resistant
heterozygous - unaffected and resistant
homozygous recessive - affected but resistant
mosaicism
present in individual or tissue of at least two cell lines that differ but come from a single zygote
somatic mosaicism
present in some tissues but not in the gametes
germ-line mosaicism
mutation is only in germ line cells
lethal alleles
homozygous genotype is lethal changing 1:2:1 to 2:1 ratoi
penetrance
some have the same genotype but not express the phenotype. when penetrance is <100% it is incomplete penetrance
variable expressivity
penetrance is all or nothing
expressivity is the severity of expression of phenotype
pleiotropy
one variant has multiple effects
genetic heterogeneity
single phenotype caused by variants at different alleles or different loci
allelic heterogeneity
different variants within a give locus can be seen with a genetic condition
locus heterogeneity
same phenotype from variants at many different loci
complementation test
test whether mutant alleles are in the same gene (non-complement) or in different genes (complement)
different gene
homozygous for mutations that show same phenotype but are in different genes, the progeny are wild-type. they complement one another
same gene
homozygous for mutations that show same phenotype but are in same gene, the progeny are mutant. they fail to complement one another
anticipation
trait becomes more strongly expressed or expressed earlier passed from one generation to generation
common caused by dynamic mutations, expansion of trinucleotide repeats in tandem
complementary gene action
both genes are required for the correct phenotype ratio = 9:7
epistasis
phenotype produced by variant of one gene that blocks or masks the phenotype of another
recessive epistasis
ratio 9:3:4. only able to block phenotype if homozygous recessive
bombay phenotype (recessive epistasis)
O blood type parent and A blood type parent making a AB offspring. due to presence/absence of substance H. it allows antigens to bind to it. if not there prevents binding.
dominant epistasis
ratio 12:3:1. if dominant allele B is present. B phenotype is present. if b is recessive and A is dominant, A phenotype is present. if both recessive other phenotype is present
duplicate genes
either dominant gene is required. 15:1
effect of environment on phenotype
- temperature
e. g. coat colour change in the arctic fox (cold = white, warm = brown - chemicals
e. g. phenylketonuria (PKU) in humans loss of enzyme to metabolise amino acid Phe. low Phe diet = good. alter environment to remove Phe
genomic imprinting
allele is transcriptionally inactive depending on parent whom you received the allele from. methylation or chromatin modifications (epigenetic changes)
sex-linked traits
inherited characteristics conditioned by sex of individual
e.g. baldness is autosomal dominant in males and recessive in females
sex-limited traits
characteristic only appears in one sex
e.g. ovary development
cytoplasmic inheritance
inheritance of parental characters through non-chromosomal DNA
mitochondrial DNA is cytoplasmically inherited since the information is not segregated at mitosis
homoplasmy
every mitochondrial genome carries the causative mutation
heteroplasmy
contain a mixed population of normal and mutant genomes in each cell
