Chapter 5 Flashcards
incomplete dominance
one allele for specific trait is not completely expressed over its paired allele
Complete dominance
dominant allele masks the effect of recessive allele
Codominance
The phenotype of the heterozygote is not intermediate between
the phenotypes of the homozygotes; rather it simultaneously
expresses the phenotypes of both homozygotes
Levels of phenotype
Anatomical, Physiological, Molecular
Pheno Level affects in CF
– Gene responsible is on chromosome 7
– Encodes a protein termed CFTR (
* CFTR -regulates chloride levels and is mutated in CF
* Mutated channel stays closed, chloride ions build up
* In heterozygotes, enough functional CFTR is made to
prevent cystic fibrosis
Incomplete penetrance
genotype is not
producing expected phenotype
Penetrance
The percentage of individuals
having a particular genotype that express
the expected phenotype
Expressivity
the degree to which a trait is
expressed
Lethal Alleles
Causes death at an early stage of development, so some
genotypes may not appear among the progeny
Affects the Mendelian
genotypic and phenotypic
ratios in progeny!
Multiple alleles:
For a given locus, more than
two alleles are present within a group of
individuals
– The genotype of each individual diploid organisms still only
consists of two alleles!
– Inheritance of characteristics encoded by multiple alleles is no
different than those encoded by two alleles
Gene interaction
Effects of genes at one locus depend on the
presence of genes at other loci
Sex-linked characteristic
Phenotype Determined by
Sex-linked characteristic Genes located on the sex chromosome
Sex-influenced characteristic
Autosomal genes that are more readily expressed in one sex
Sex-limited characteristic
Autosomal genes whose expression is
limited to one sex
Genetic maternal effect
Nuclear genotype of the maternal parent
Cytoplasmic inheritance
Genetic maternal effect Cytoplasmic genes, which are usually
inherited from only one parent
Genomic imprinting
Genes whose expression is affected by the
sex of the transmitting parent
Epigenetics:
phenomena due to alterations to DNA that
do not include changes in the base sequence; often affect
the way in which the DNA sequences are expressed
Genetic Maternal Effect
– phenotype of the
offspring is determined by the genotype of the
mother.
Characteristics of cytoplasmically
inherited traits
- Present in males and females.
- Usually inherited from one parent, typically the maternal
parent. - Reciprocal crosses give different results.
- Exhibit extensive phenotypic variation, even within a single
family
Duplicate Recessive Epistasis –
Two recessive alleles at
either of two different loci are capable of suppressing a
phenotype
Dominant Epistasis
Only a single copy of an allele is required to inhibit
the expression of an allele at a different locus.
Recessive epistasis:
‒ Presence of two recessive alleles inhibits the expression of an
allele at a different locus.
‒ Labrador retriever coat color is determined by interactions
between genes at two loci
‒ One locus determines pigment produced by skin cells
‒ Second locus affects the deposition of the pigment into the shaft
of the hair.
epistatic gene.
The gene that does the masking
hypostatic gene.
The gene whose effect is masked
