Genetics Unit 3

Dominant

Shows when only one copy is present

Recessive

Shows when two copies are present

Haplosufficient

Wild-type dominant if one copy is enough for normal function in heterozygotes

Haploinsufficient

Wild-type recessive if one copy is not enough for normal function

WT baseline

Loss of function

Decrease or loss of functional gene product, can be a null/apomorphic mutation or a leaky/hypomorphic mutation

Null/apomorphic mutation

Loss of function; produces no functional gene product, lethal when homozygous

Leaky/hypomorphic mutation

Loss of function; partial loss of function, usually but not always recessive, the same product is produced but there's less of it

Dominant negative mutations

When homozygous, creates a mutated product that has an abnormal effect with the gene product of another, multiple gene products are impacted and not just their own

Gain of function

Increase or change of gene products

Hypermorphic

Gain of function; more gene products produced

Neomorphic

Gain of function; Mutation causes new functions

Incomplete/partial dominance

Intermediate phenotype for a heterozygous blend, ex. CrCr is red and CwCw is white, CrCw makes pink, then when CrCw self-fertilizes, 1

Codominance

Both genes are expressed at the same time, ex. white cow and brown cow makes a cow with brown and white markings

Allelic series

Multiallelic genes effect the order of dominance, ex. C is dominant over all alleles, a few alleles are partially dominant then all alleles can be dominant over one allele

Lethal alleles

Mostly recessively inherited, only homozygous dies, distortions in segregation ratios, embryonically lethal when recessive, shows later in life when dominant; ex. Ay is a visible dominant mutant allele that gives mice yellow coats instead of brown, Ay is recessive embryonic lethal, AyAy is lethal but AAy is not lethal; recessive lethal and dominant visible

Delayed age of onset

Dominant lethal alleles, ex. Huntington's disease doesn't show until late 30s early 40s, you need only one copy for lethality, you can reproduce before it kills you so it passes on

Sex-limited traits

Sex-specific gene expression, both sexes carry the genes for a trait but only one sex expresses the trait, ex. lactation is female-specific

Sex-influenced traits

Sex influences expression of trait, both sexes express the trait to varying degrees, dominant in one sex but recessive in the other sex

Penetrance

When the phenotype is consistent with the genotype, a trait is penetrant, if the genotype is always expressed in phenotype -> fully penetrant, sometimes genotype and phenotype match -> incompletely penetrant; ex. polydactyly, you can have the allele to have extra fingers but you don't have extra fingers

Variable expressivity

Varying degree of severity in phenotypic expression, same genotype with different combination of symptoms

Pleiotropy

One gene affects multiple traits, ex. sickle cell also affects the eyes, liver, and heart

Epistasis

One gene masks or modifies the phenotype of a second gene, dihybrid traits, all phenotypic ratios stem from 9;3;3;1

Complementary

9;7, both precursors are needed to get the colored phenotype, two gene interactions needed to get the color

Duplicate gene action

15;1, at least one dominant is needed to get the colored phenotype, double recessive is colorless

Dominant

9;6;1, two dominant alleles make one phenotype, recessive allele for one gene and dominant allele for the other gene makes one phenotype, double recessive makes a phenotype

Recessive epistasis

9;3;4, homozygous recessive alleles mask the phenotypic expression of alleles at a second locus

Dominant epistasis

12;3;1, dominant allele will mask phenotypic expression of alleles at a second locus

Dominant suppression

13;3, dominant allele prevents expression of the second locus

Syntenic genes

Genes on the same chromosome, alleles cannot sort independently and are called linked genes, if the genes are far apart enough independent assortment can happen

Recombinant chromosomes

Homologs cross over and undergo recombination, making them this

Parental chromosomes

Does not undergo recombination, unchanged

Genetic linkage

Frequency of gamete genotype to progeny phenotypes, if linked parental alleles are higher frequency

Complete genetic linkage

No crossover, only parentals

Incomplete genetic linkage

Crossover, parentals are still most common

Recombination frequency

Represented by r, calculated b the number of recombinants over the total number of progeny, higher r means further apart, if r is less than 0.5 then the traits are linked, parental alleles will always be 50% of the progeny at least since crossover only happens between two chromatids not all four

Linkage map

Using r values, sees how far apart genes are from each other, measured in m.u (map units) or cM (centimorgans)

Recombination hotspot

Places where crossover is more common, makes genes seem further apart than they are

Recombination coldspot

Places where recombination rarely happens if ever, usually around the centromere

Haplotype

Two loci close together, two alleles that are often if not always inherited together