Lecture 2 Flashcards
incomplete dominance
heterozygote shows a mixture of two alleles–phenotype varies in proportion to the amount of protein
codominance
traits of both alleles show up in the phenotype for heterozygotes– neither phenotype is recessive
non-mendelian inheritance
when the inheritance of phenotype is not as clear cut as Mendel observed in his experiments for inheritance of alleles
penetrance
the percentage of INDIVIDUALS with a specific genotype that exhibit the expected phenotype (it’s a population thing)
expressivity
the degree that a given genotype is expressed phenotypically in ONE INDIVIDUAL
cytoplasmic inheritance
inheritance due to NON-chromosomal mutations via female gametes (can be from mitochondria or chloroplasts)– literally only the female’s genotype matters
endosymbiosis
evolutionary theory that eukaryotic cells arose from prokaryotes (mitochondria have their own circular DNA, they have similar sized ribosomes 70S, double membrane, same size as bacteria, and can be produced by division of pre-existing mitochondria and chloroplasts)
heteroplasmy
the presence of more than one type of organelle genome (occurs when mitochondrial DNA from sperm leaks into egg cytoplasm at time of fertilization–very rare)
proband
Person being studied
propositus
male
proposita
female
Assumptions with disease-causing mutations:
- Affected individuals for a dominantly inherited trait are usually heterozygous - For recessively inherited diseases, most unrelated individuals will not be carriers
TRAITS OF A PEDIGREE– autosomal recessive
- -unaffected parents with affected progeny
- -m/f equally affected
- -rare phenotype in general population
- if affected individuals do not appear in every generation, it is recessive
TRAITS OF A PEDIGREE– autosomal dominance
- phenotype occurs in every generation
- affected parents transmit phenotype to both sons and daughters
- roughly half of children of affected individuals will show phenotype
TRAITS OF A PEDIGREE– X-linked dominant
- affected female transmits to male and female equally
- affected male transmits to 100% daughters, 0% sons
For both x-linked traits, fathers can never pass sex-linked traits to sons
TRAITS OF A PEDIGREE– X-linked recessive
- only females are carriers
- carrier female will transmit to 50% sons (affected) and 50% daughters (carriers)
- affected male cannot transmit to sons but 100% of daughters are carriers
For both x-linked traits, fathers can never pass sex-linked traits to sons
TRAITS OF A PEDIGREE– Y-linked inheritance
- only from father to sons
- no daughters affected
Since most Y-linked genes involved in spermatogenesis, mutations can cause sterility and are unlikely to be passed down
TRAITS OF A PEDIGREE– mitochondrial DNA inheritance
- moms pass to everyone
- affected males do not transmit mtDNA or the disease phenotype
Baye’s Theorem
helps to determine carrier status of an individual in a pedigree
If a diploid organism is heterozygous at six different gene loci, e.g. Aa;Bb;Dd;Ee;Gg;Hh, how many different gametes would they make?
2^6 gametes
Use equation 2^n, with n being the number of heterozygous genes
null mutation (amorph)
a mutation that gives no function, even if the protein gets made
silent mutation
mutation that occurs either in a noncoding region, or does not change the amino acid coding for it
leaky mutation (hypomorph)
partial loss of function– gene sits on the border of an active site of chromosome
Why are x-rays so damaging to DNA?
Because they break both strands of DNA, really hard to repair
How might one distinguish a hypomorph from an amorph?
Take a deletion-removing segment of DNA, cross the deletion with the either hypomorph or amorph so that the only functional copy is the mutation. If it looks worse, you’ve got a hypomorph, if it looks the same, you’ve got an amorph (loss of function)
hypermorph
more than usual function–activity of the gene is increased either by increasing the amount of the protein or the protein’s efficiency
neomorph
uncommon– mutation that results in a new function of the mutant gene, often (but not always) with loss of the normal function
antiomorph
uncommon– gain of function mutation that acts in opposition to the normal gene’s function, usually dominant or incomplete dominant (stronger than null)
haplosufficiency
one copy is enough for it to function normally–wild-type is dominant to mutant
haploinsufficiency
mutant allele is dominant to wild-type because individuals heterozygous or homozygous for the mutant allele are both mutant in phenotype
pleiotropic allele
a single chromosomal mutation that affects several different characteristics (multiple phenogypes)
Agouti is a recessive lethal pleiotropic allele for huge mice–since recessive lethal ones are dead, viable ones can only be heterozygous
