Gene Action Flashcards
What is gene action?
How the genotype of a particular trait affects the expression in phenotype
What are the types of gene action?
non-additive, sex-linked, sex-limited, sex-influences, and additive
What is non-additive?
one allele is expressed stronger than the other allele for the phenotype (1 allele controls phenotype?
What are sex-limited traits?
expression of this trait is limited to the sex
What are sex-influenced traits?
inheritance of a trait appears to be different in the 2 sexes even when they have the same genotype
What are additive traits?
two alleles contribute equally to the phenotype
What are sex-linked traits?
genes on the sex chromosome determine the phenotype, it affects the way genes are expressed
What are examples of sex-linked traits?
hemophilia, colorblindness, and muscular dystrophy
What is are examples of a sex-limited trait?
milk production, egg production, and crytorchidism
What is an example of sex-influenced traits?
male pattern baldness, horned or polled?
What are qualitative traits controlled by?
controlled by one or few genes
Which type of gene action are qualitative traits?
non-additive
What are the types of non-additive gene action?
complete dominance, incomplete dominance, and epistasis
What is complete dominance?
one allele of a pair can mask the expression of the other (recessive)
recessive expression=?
homozygous condition
What is an example of complete dominance?
Angus cattle have black fur (BB or Bb) and Hereford have red fur (bb)
What is incomplete dominance?
when heterozygous, there is a different phenotype
What is an example of incomplete dominance?
shorthorn cattle with RR is red, Rr is roan, and rr is white
What are the ratios of a incomplete dominance cross of RrxRr?
genotype: 1 RR: 2 Rr: 1 rr
phenotype: 1 red: 2 roan: 1 white
What is a heterozygote phenotype called for goats (long ear x short ear)?
medium
What is a heterozygote phenotype called for horse (chestnut x cremello)?
palomino
What is a heterozygote called for chickens (black x white)?
blue
What is epistasis?
interactions between non-allelic genes; the phenotypic effect of genes at one locus is dependent on what alleles are present at another locus distinct from the first locus
What are the types of epistasis?
Complete dominance epistasis, recessive epistasis, and no dominance (incomplete dominance)
What is complete dominance epistasis?
dominant alleles of one gene control the other
What is recessive epistasis?
homozygous recessive alleles of one gene control the other
What is no dominance epistasis?
heterozygous acts as a separate phenotype, and affects the other gene
What is sex determined by?
inheritance of entire chromosome
trait controlled by locus on X chromosome=?
relationship with inheritance of sex
Y chromosome=?
very few loci identified as controlling traits unrelated to sec of the individual
What does the X chromosome carry?
genes for many traits
What is an example of a sex-linked trait in animals?
color in cats
What is sex-linkage?
concerned with the inheritance of traits controlled by alleles on X chromosome (trait is affected by gene on sex chromosome)
What is CCB_?
bay
What is CcB_?
buckskin
What is cc__?
cremello
What is Ccbb?
palomino
What is CCbb?
chestnut
What are example of purebreeding in terms of cat coat color?
X linked black cats, also orange
What do orange and black cats intermating result in?
tortoise shell
What kind of coat color is tortoise shell?
codominance of orange and black alleles
Why are not all black and orange cat offspring torts?
must classify kittens by sex and color
How can there be a male tort?
XXY chromosome
What is XXY called in humans?
Klinefelter syndrome
What must a cat have in order to be a tort?
both black and orange alleles
What offspring will female torts produce?
different constitutions depending on the genotype of mate
How do females show recessive sex-linked traits?
homozygous
How many sons have recessive phenotype of a recessive sex-linked trait when heterozygous mother?
50%
How do calico cats work?
creation of barr bodies and piebald; x chromosome inactivation
What is piebald?
having 3rd color gene, allows for expression of white
What is x chromosome inactivation?
for females, only one X needs to be activated. The activated ones will form patch of fur that color
What are barr bodies?
inactivated chromosome
How does the presentation of polled or horned appear in males?
horned is dominant
How does the presentation of polled or horned appear in females?
polled is dominant
What type of gene action is baldness?
sex-influenced
What is cryptorchidism?
when one (mono-) or both of the testes fail to descend from the abdomen
What is pleiotropy?
one gene affects more than one trait
What is variable expressivity?
the existence of more than one grade of trait
What is overdominance?
interactions between gene alleles resulting in a heterozygote superior to either homozygote for a particular trait; extreme heterozygote
What is genetic correlation a result of?
1) pleiotropy
2) gene linkage
What is grade?
range
What is an example of overdominance?
sickle cell disease; heterozygotes carry sickle cell but don’t have it and are resistant to malaria
What is incomplete penetrance?
not all animals with a particular genotype exhibit the phenotype for that phenotype
What is an example of incomplete penetrance?
polydactyly in fowl, humans, dogs, and cats
What is variable expression?
range of expression of a phenotype
What does a lethal gene refer to?
embryonic death, shortly after birth
What does semi-lethal gene refer to?
death before puberty
What does detrimental gene refer to?
reduction in some measure of fitness or productivity
What kind of death is a horse who dies 2 months after birth?
lethal
Which type of lethal/detrimental gene can be predicted?
semi-lethal
What type of lethal/detrimental gene do albino giraffes have? Why?
detrimental; anti-social behavior and highly detectable
What type of lethal/detrimental genes are shorter dwarfism in cattle?
HH= normal Hh = comprest (slow growing/poor development)-detrimental hh = semi-lethal (death before puberty)
What is an absence of phenotype?
when a genotype is lethal it results in no possible phenotype outcome
What is an example of absence of phenotype?
In platinum foxes, PP is lethal. When crossing Pp x Px you get 2Pp:1pp instead of 1PP:2Pp:1pp
What is the early embryonic mortality rate of swine?
20-30%
What is the early embryonic mortality rate of cattle?
10-20%
What is gene linkage?
a condition where non-allelic genes (different traits) consistently travel together through meiosis and syngamy
What is syngamy?
the fusion of 2 cells in reproduction
How are loci affected by gene linkage?
2 loci are linked if they occur on the same chromosome
In terms of gene linkage (?) what happens to homologous chromosmes?
separated at meiosis; genes on the same chromosome tend to end up in the same gamete
What is the exception to gene linkage?
crossing over
What is crossing over?
reciprocal exchange of chromosome segments between homologs
What is the crossing over process?
mutual breaks occur at identical sites on each chromosome, chromosome fragments are exchanged
What is recombination?
formation of new combination of genes on a chromosome as a result of crossing over
Are cross over events common?
multiple are
What does the probability of recombination of genes at any two linked loci depend on?
the distance between the loci
What can the occurrence of crossing over help determine?
the sequence of genes on a chromosome
Where does crossing over occur more?
between distant genes than genes that are close together
What are quantitative traits controlled by?
many genes
What are quantitative traits?
expression over continuous range of values
What are examples of quantitative traits?
milk production and carcass merit
What is carcass merit made of?
IMF (intramuscular fat), REA (rib eye area), and FT (fat thickness)
Are qualitative traits affected by the environment?
no
Are quantitative traits affected by the environment?
largely (housing, nutrition, etc)
How do genes contribute to the phenotype in quantitative?
each gene contributes a certain amount toward phenotypic expression
What are qualitative traits?
yes or no trait (there or not there)
What are types of quantitative traits in beef cattle?
growth rate, carcass trait, reproductive traits
What are the factors of growth rate?
birth weight, weaning weight, yearling weight, average daily gain (ADG)
What are the factors of reproductive traits?
calving ease, yearling pregnancy, scrotal circumference, first service conception, stagability
What is calving ease?
selecting against dystocia
Why is scrotal circumference selected for?
measure of fertility and relation to the age of puberty in offspring
What is first service conception?
select for ones who can get pregnant on first service (first AI)
What is stagability?
produces one calf a year for constantly 3 years
What are some reproductive traits for poultry?
fertility of eggs, hatchability, laying persistence, age to first egg
What does selecting the best offspring do?
shift the mean in the positive direction (quantitative)
Is heritability a trait?
no
What is heritability represented by?
h^2
What are the two senses of heritability?
broad and narrow
What is the broad sense of heritability?
ratio of genetic variance to phenotypic variance
What is the formula for the broad sense of heritability?
h^2=Vg/(Vg+Ve)
What is the narrow sense of heritability?
proportion of genes expected to be passed from parent to offspring that contribute to expression of that trait
What is the formula for the narrow sense of heritability?
h^2=Bv/Vp
What is the formula for Vp?
Vp=Vg+Ve
What is the formula for Vg?
Vg = Bv+GCV
What does Bv stand for?
breeding value
What does GCV stand for?
gene combination value
What is narrow sense of heritability used for? Why?
animal breeding because it is more reliable as it looks at breeding value
What is broad sense of heritability used for?
humans
What is h^2 a measure of?
additive gene action
How is heritability expressed?
on a range from 0.01 to 1
What is low heritability range?
0.01-0.2
What is medium/moderate heritability range?
0.21-0.4
What is high heritability range?
> 0.41
What traits have low heritability?
reproductive, fertility, and survival
What traits have medium/high heritability?
growth and carcass
What does a highly heritable trait mean?
high performance animals produce high performing offspring, low performing animals produce low performing offspring
What does a lowly heritable trait mean?
performance records of parents reveal little progeny performance
Are all traits heritable?
no, some traits show no phenotypic differences, even though they are genetically determined
What is an example of a non-heritable trait? Why?
number of legs in dogs, because it is standard for dogs to have 4 (leg length on other hand is heritable)
What are the parts of additive gene action?
quantitative traits and heritability
