Chapter 3d - Genes of Variable Expressivity Flashcards
Genes of Variable Expressivity
- Pleiotropy
- Penetrance
- Phenocopy
single mutation simultaneously affects several traits
pleiotropy
examples of pleiotropy
- sickle cell anemia
- phenylketonuria (PKU)
- Marfan syndrome
- porphyria variegata (vampire’s disease)
what does the alleles of the b–globin gene influence
- type of hemoglobin produced
- red blood cell shape
- susceptibility to anemia
- malaria resistance
- organ function
- life-span
- rare inherited disorder that causes an amino acid called phenylalanine to build up in the body
- caused by a change in the phenylalanine hydroxylase (PAH) gene. This gene helps create the enzyme needed to break down phenylalanine
phenylketonuria (PKU)
caused by defects in gene called fibrillin-1, an important building block for connective tissues in the body
Marfan Syndrome
manifestations of Marfan Syndrome
- Pectus excavatum
- arachnodactyly
- dilation of aorta
- group of rare, genetic blood disorders that impact the production of hemoglobin, the iron-rich protein that transports oxygen in the blood
- Cutaneous porphyrias (porphyrias affecting the skin) leads to sensitivity to sun and light
porphyria variegata (vampire’s disease)
Ex. of people with Marfan Syndrome
- Abraham Lincoln
- Osama bin Laden
Ex. of people with porphyria variegata
- King George III
- Vincent van Gogh
- Nebuchadnezzar
- Paula Frias Allende
given genotype may or may not show phenotype
penetrance
Two types of penetrance
- complete penetrance
- incomplete penetrance
all individuals express a given genotype
complete penetrance
not all would express a given genotype
incomplete penetrance
ex. of incomplete penetrance
- Harelip
- Dominant retinoblastoma
- malignant eye tumor in children
- 90% penetrance
dominant retinoblastoma
when penetrant:
degree in which a particular phenotypic effect is exhibited in an individual
expressivity
two types of expressivity
- constant expressivity
- variable expressivity
trait in all individuals is identical
constant expressivity
ex. of constant expressivity
- kinky hair
- vestigial wings in Drosophila
not identical expression of trait
variable expressivity
ex. of variable expressivity
- polydactyly
- mouse spotting
penetrance and expressivity
- penetrance, with complete expression
- penetrance, with moderate expression
- penetrance, with minimal expression
- no penetrance, thus no expression
what influence the degree of penetrance and expressivity
- modifier genes
- environment
identical known genotypes yield 100% expected phenotype
complete penetrance
identical known genotypes yield <100% expected phenotype
incomplete penetrance
identical known genotypes with no expressivity effect yield 100% expected phenotype
constant expressivity
identical known genotypes with an expressivity effect yield a range of phenotypes
variable expressivity
identical known genotypes produce a broad range of phenotypes due to varying degrees of gene activation and expression
incomplete penetrance with variable expressivity
- environmentally-induced phenotype which closely resembles the phenotype by a known recessive gene
- or ‘aritifical phenotype’
phenocopy
ex. of phenocopy
- insulin-dependent diabetics
- thalidomide babies
- phenylketonuria of normal babies with mothers with PKU
- used as sleeping pill and tranquilizer in the early 1960s taratogenic when used during the first trimester of pregnancy
- mimics a recessive disorder, phocomelia, characterized by abnormalities in the bones of arms and/or legs
thalidomide
what does thalidomide babies mimic
phocomelia
what helps determine expression of genotype
environmental conditions
what changes the color of hydrangea flowers
pH of soil
carries allele specifying heat-sensitive enzyme for melanin production
himalayan rabbit
some effects of the environment
- age of onset (male pattern baldness)
- sex (male pattern baldness)
- temperature
what does temperature influene
- enzymes
- coloration in Siamese cats
- sex determination in reptiles
occurs more often in females than males due to the presence of estrogen
rheumatoid arthritis
baldness:
BB
bald in either sex
baldness:
Bb
bald in males only
baldness:
bb
normal hair in both
- traits where an allele is dominant in one sex but recessive in the opposite sex
- does not mean sex-linked
sex-influenced traits
sex influence is a phenomenon of __
heterozygotes
sex-influenced traits are __, meaning it is not sex-linked
autosomal
ex. of sex-influenced traits
scurs (hornlike growth) in cattle
found in both sexes but manifested only in one sex due to physiological/anatomical reasons
sex-limited traits
ex. of sex-limited traits
- genes for milk production in both bulls and cows
- genes for long pointed feathers in cocks and hens
- genes for beard development in men and women
