chapter 4 part 2 Flashcards
what is the C gene responsible for in mammals
coat color
what does C gene produce
enzyme involved in melanin production
allelic series of C gene
C, c(ch), c(h), c
how many alleles are there of the C gene?
dozens
C
produces functional enzyme (tyrosinase enzyme that is 100% active) and full coat color
c(ch)
produces dilute phenotype called chinchilla
c(H)
produces phenotype called Himalayan with little pigment on body but full color on extremities
c
fully recessive null allele and produces an albino phenotype (amorphic)
is the C allele haplosufficient or haploinsufficient
haplosufficient
activity of enzyme produced by c(ch)
less than 20% active - hypomorphic
how is the c(h) allele temperature-sensitive?
- functional at lower temperatures (extremities)
- non-functional at higher temperature (core)
lethal alleles/mutations
inherited as recessive alleles (all homozygotes die)
how are lethal alleles detected
can be detected as distortions in segregation ratios caused by 1+ missing classes of progeny
what is the Agouti Locus an example of
lethal alleles
Agouti Locus
- wild type coat color in mice = agouti, produced by combo of yellow/black pigments along each hair
- Ay - dom allele, causes yellow pigment along entire hair in heterozygotes
- Ay lethal in homozygous state
all yellow mice are _____________
heterozygous
outcome of cross A/Ay x A/Ay
1/4 AA Agouti
1/2 AAy yellow
1/2 AyAy, pre-implantation embryonic lethal
the Ay allele is…
- dominant for yellow coat color
- recessive for survival
what is the Ay mutation caused by
deletion that affects 2 genes, Agouti and RAly
Ray gene
produces protein essential for mouse development
what does the deletion between Agouti and Raly genes do
connect the Ray promoter to the Agouti gene, which destroys the Raly coding sequence
why do homozygous AyAy mice die?
due to lack of Raly protein, never implant in uterus
ex. of how genotypic and phenotypic ratios are complicated
- delayed age of onset
- sex-limited traits
- sex-influenced traits
- incomplete penetrance
- variable expressivity
- environmental modification
- pleiotropic effects
delayed age of onset
abnormalities of dominant lethal alleles not expressed until after affected ind. has reproduced
how can dominant lethal alleles sidestep natural selection?
delayed age of onset
ex. of delayed age of onset
Huntington Disease
Huntington Disease
fatal neurodegenerative disorder which doesn’t usually show symptoms until late 30s/40s
sex-limited traits
both sexes carry the genes for such traits, but they are expressed only in one sex
ex. of sex-limited traits
- mammalian breast and ability to produce milk = female
- horn development sometimes limited to males
- behavioral traits
what differentially influence the expression of genes and sex-limited traits?
sex hormones
the sex of an organism can influence gene expression due to ____________ ____________ _____________
differing hormone profiles
sex-influenced traits
those in which the phenotype corresponding to a particular genotype differs depending on the sex of the organism
ex. of sex-influenced traits
chin beard in certain goat breeds
- heterozygous for beard: phenotype influenced by presence/absence of androgenic (male) hormones
penetrance
observed phenotype is consistent with genotype
non-penetrance
phenotype associated with genotype is not visible
fully penetrant
when expected phenotype is always expressed from a particular genotype
incomplete penetrance
traits/genotypes that are nonpenetrant in a portion of the population
ex. of penetrance
polydactyly - dominant allele is non-penetrant in about 25-30% of ind. carrying it
polydactyly
autosomal dominant condition in which affected individuals have 5+ fingers and toes
variable expressivity
seen in ind. who show a phenotype but to a varying degree of severity
ex. of variable expressivity
Waardenburg syndrome - same genotype with different combination of symptoms
4 principal features of Waardenburg syndrome
- premature graying
- white forelock
- hearing loss
- different-colored eyes
ex. of environmental modification to prevent disease
phenylketonuria (PKU)
phenylketonuria
autosomal recessive condition caused by the absence of an enzyme involved in phenylalanine breakdown
hereditary disorder routinely screened for in infants
PKU
what is the inability to break down phenylalanine toxic to
developing neurons
key to preventing PKU
restricting phenylalanine in diet of infants
- can help people live normal lives
pleiotropy
alteration of multiple distinct traits by mutation in single gene
- one gene has many effects
ex. of pleiotropic gene
sickle cell disease
sickle cell disease
autosomal recessive condition caused by mutation in B-globin gene
- red blood cells take on sick shape and cause numerous physical problems and conditions
gene interaction
collaboration of multiple genes in the production of a single phenotypic characteristic or group or related characteristics
anabolic pathways
involve biosynthesis of complex compounds
catabolic pathways
involve degradation of complex compounds
ex. of pathways that involve interaction of multiple genes
signal transduction, developmental pathways
what does epistasis literally mean
“stands upon”
epistasis
alleles of one gene modify or prevent expression of alleles of another gene
mutation of one gene in a pathway may prevent what?
production of end product
what can gene interaction lead to
altered phenotypic ratios of wild type and mutant progeny
where is epistasis readily detected
among progeny of dihybrid crosses involving genes w/ both dom and rec alleles
no interaction ratio
9:3:3:1
no interaction
- absence of epistasis
- genes don’t interact to change expression of one another
complementary gene interaction
two genes must interact to produce overall phenotype - when genes work in tandem to produce a single gene product
duplicate gene action
redundant system in which a dominant allele at either locus gives rise to a wild type phenotype
- encode same product, or encode products that have same effect in pathway
complementary gene interaction ratio
9:7
duplicate gene action ratio
15:1
dominant gene interaction ratio
9:6:1
dominant gene interaction ex
- summer squash have disk shaped fruit if at least one dom allele expressed
- 1 of 2 dom alleles gives round fruit
- only recessive gives long fruit
recessive epistasis ratio
9:3:4
recessive epistasis ex.
labradors
- one gene responsible for eumelanin production
- second gene responsible for distribution of pigment on hairs
- dogs that can’t produce eumelanin or distribute pigment have yellow coat
recessive epistasis
homozygosity for recessive alleles at one locus will has the phenotypic expression of the alleles at a second locus
dominant epistasis ratio
12:3:1
dominant epistasis
dominant allele at one locus will bask the phenotypic expression of alleles at second locus
dominant suppression ratio
13:3
dominant suppression
dominant allele at one locus completely suppresses the phenotypic expression of alleles at second locus
ex. of no interaction
green, blue, and yellow parrots
ex. of complementary gene interaction
purple and white flowers
ex. of duplicate gene action
purple and white flowers
ex. of dominant gene interaction
squash (disk, sphere, and long)
ex. of recessive epistasis
labradors
ex. of dominant epistasis
white, yellow, and green squash
ex. of dominant suppression
white and blue flowers
