Unit 6 - extensions of Mandelean Genetics Flashcards
what is a typical case of Mandelean Genetics
Mandel chose to examine traits with just two alternative forms (Dominant and recessive). In this case phenotypes would display only one of two forms; Dominant (AA/Aa) and Recessive (aa)
How alleles create a phenotype (3)
*the overall phenotype of an individual is the consequence of the protein products for the allele of said gene
*For example: A wild-type allele R+ produces 50 units of an active enzyme and a mutant allele r produces little or no active enzyme (0 units). For this case 40 units of said enzyme will produce the wild-type phenotype. So RR individuals have 100 units, Rr have 50 and rr have 0. So the rr type does not express the wild-type phenotype.
*Genes Like R+ are considered to be haplosufficent, meaning only one copy is required for normal function. If it were to say only produce 20 units, it would be haploinsufficent, as one copy is not enough for normal function.
Loss-of-Function mutations (3)
*Mutation causes a significant decrease or complete loss of function gene product
*Loss-of-function mutation that produce no functional gene product are called null mutations or amorphic mutations, and are often lethal when homozygous
*multimeric proteins (made of two or more polypeptides joined together to make a protein) are susceptible to dominant negative mutation, which prevent the polypeptides from interacting normally
Gain-of-function mutations (3)
*Are usually dominant
*Can be hypermorphic and produce more gene activity than normal (hyper =more)
*or neomorphic where gene activity not found in the wild type is produced (neo = new)
incomplete dominance (3)
*Notation is slightly different (A1 and A2 instead of A and a)
*Also called partial dominance
*is when heterozygous individuals display an intermediate phenotype (IE parents are red and white but child is pink)
Codominance (3)
*Codominance leads to heterozygotes with a different phenotype than that of either homozygote
*Both alleles are expressed in this case
*for example a black cow and white cow mate creating a black and white cow
Allelic series (3)
*for some gene, a single locus may have more than one allele, this is said to have multiple alleles
*An order of dominance among these alleles forms a series called an allelic series
*for example, in rabbits the allele C is responsible for coat color. A single loci may have one or all of C, Cch, ch, or c, where C is dominant to Cch, which is dominant to ch, which is dominant to c.
Lethal alleles (3)
*Some single-gene mutation are so shit that they literally kill a Mf (not always directly, for example it would suck to be a black arctic fox = lethal allele)
*these are called lethal Alleles (duh?) and are recessively inherited (only homozygotes die)
*Typically occur in very low frequencies
Lethal Alleles in plants (4)
*In plants, lethal alleles can be either Embryonic or gametophytic.
*Embryonic lethals fail to produce progeny and can be detected with a 3:1 (living : dead) ratio of seeds
*when living seeds are planted, they produce a 2:1 (heterozygous : homozygous rec) ratio
*Gametophytic lethals fail to generate gametes
Lethal Alleles in Animals (2)
*can be detected by having missing classes of prodigy
*for example : mice the A codes for yellow pigment, and R codes for an essential protein. An Allele mutation, causes the promoter to bind to A rather than R, so in heterozygotes, the mice have yellow fur but still produce the essential protein (from the copy of the gene), but in homozygotes, the protein is not produced and they die!
Delayed age of onset (3)
*dominant lethal alleles can dodge-roll natural selection if they have a delayed age of onset
*IN this case, the abnormalities they produce are not evident until after the individual has reached reproductive age
*and example of this is Huntington disease, a fatal disorder that does not usually show symptoms until the affected individual is in their late 30s/40s
Sex-limited traits (2)
*the Sex of an organism can infliuence gene expression due to different hormones present
*These traits are known to be sex-limited; where both sexes carry the genes but they are only expressed in one sex
*for example , female nipples producing milk where males do not
Sex-influenced traits
*the phenotype corresponding to a particular genotype differs depending on the sex of a organism
*for example, both BB male and female goats have beards, and bb one do not. In males Bb has beard, in females they do not.
Penetrant types (4)
*An organism is penetrant for a trait when the phenotype is consistent with the genotype
*an organism that does not produce the phenotype generally associated with its genotype is nonpenetrant
*When the genotype is always expressed in the phenotype, the trait is fully penetrant
*traits that are penetrant in some individuals and nonpenetrant in others are called incomplete penetrance
Variable Expressivity
*In variable expressivity, individuals who carry the alleles for a trait show a phenotype, but to varying severity
*for example a hypothetical trait that causes blindness, hearing loss, and mobility loss (Hellen Keller syndrome), some individuals may be blind and deaf, some my be just blind, some my be just deaf etc.
