Chapter 5. Extensions of Mendelian Inheritance Flashcards
Simple Mendelian inheritance describes the inheritance patterns that obey
- The Law of Segregation
- The Law of Independent Assortment
Simple Mendelian
Inheritance: Follows strict dominant/ recessive relationship
Molecular: Dominant allele encodes a functional protein, 50% to produce a dominant trait
X-linked
Inheritance: inheritance genes located on X chromosome. Males have one x while females have 2.
Molecular: Males always express the copy they carry.
Incomplete Penetrance
Inheritance: When a dominant phenotype is not expressed even though an individual carries a dominant allele.
Molecular: A dominant gene may be present but not expressed due to environmental factors or other genes
Incomplete Dominance
Inheritance: Occurs when the heterozygote has a phenotype that is intermediate between either corresponding homozygote.
Molecular: 50% of functional protein is not enough to produce the same trait as a homozygote with 100% of the same protein.
Overdominance
Inheritance: When a heterozygote has a trait that confers a greater level of reproductive success than either homozygote has.
Molecular: 3 main ways:
1. cells may have increased resistance to infection by microorganisms.
2. may produce more forms of protein dimers with enhanced function.
3. may produce proteins that function under a wider range of conditions.
Codominance
Inheritance: When a heterozygote expresses both alleles simultaneously without forming an intermediate phenotype.
Molecular: The codominant alleles encode proteins that function slightly differently from each other, and the function of protein in heterozygotes affects the phenotype uniquely
Sex-influenced inheritance
inheritance: effect of sex on the phenotype of the individual.
molecular: sex hormones may regulate the molecular expression of genes. This regulation can influence the phenotypic effects of alleles.
Sex-limited inheritance
Inheritance: trait occurs in only one of the two sexes.
Molecular: sex hormones may regulate the molecular expression of genes. Sex hormones that are primarily produces in only one sex are essintial for an individual to display a particular phenotypye.
Lethal Alleles
Inheritance: has the potential to cause death to an organism
Molecular: most commonly loss-of-function alleles that encode proteins that are necessary for survival.
2 reasons to understand Mendelian inheritance
- Predict the outcome of crosses
- how the molecular expression of genes can account for an individual’s phenotype
Wild-type allele
most prevalent version of a gene in wild populations
genetic polymorphism
more than one common allele that is considered wild-type
mutant allele
a less common version of a gene
How is one wild-type copy sufficient to provide full function?
- 50% of normal levels of protein are good enough.
- the one wild-type copy is unregulated in expression.
Dominant mutant alleles are….
less common in natural populations,
3 types of dominant mutant alleles
- Gain-of-function
- Dominant-negative
- Haploinsufficiency
Gain-of-function
- gene gains new or abnormal function
- may be overexpressed, producing higher levels of the protein
Dominant-negative
mutant protein acts to antagonize the normal protein
Haploinsufficiency
the mutant is a loss-of-function allele, and one wild-type copy is not enough to provide a function
What can explain incomplete penetrance and variable expressivity?
- environment
- modifier genes
Incomplete Dominance
heterozygote exhibits a phenotype that is intermediate between the phenotypes of the two homozygotes.
Overdominance
a heterozygote has greater reproductive success than either homozygote.
3 explanations for overdominance at the molecular/cellular level
- Disease resistance
- Subunit composition of proteins
- differences in protein function
Codominance
Many genes have multiple alleles (3 or more)
Sex-Influenced Traits
an allele is dominant in one sex but recessive in the other
Sex-Limited Traits
traits that occur in only one of the two sexes
Lethal Alleles
has the potential to cause the death of an organism
essential genes
required for survival
Nonessential genes
not required for survival
Pleiotropy
multiple effects of a single gene on the phenotype of an organism
Gene interactions
occur when two or more different genes influence the outcome of a single trait
Epistasis
an inheritance pattern in which the alleles of one gene mask the phenotypic effects of the alleles of a different gene
Complementation
a phenomenon in which two different patterns that express the same or similar recessive phenotypes produce offspring with a wild-type phenotype.
Gene modification
a phenomenon in which an allele of one gene modifies the phenotypic outcome of the alleles of a different gene
Gene redundancy
a phenomenon in which the loss of function in a single gene has no phenotypic effect, but the loss of function of two genes has an effect. Functionally if only one of the two genes is necessary for a normal phenotype; the genes are functionally redundant.
Complementation
Each recessive allele (c and p) is complemented by a wild-type allele (C and P). This phenomenon indicates that the recessive alleles are in different genes.
Epistasis
when a gene can mask the phenotypic effects of another gene
Gene modification
allele of one gene modifies the phenotypic outcome of a different gene
Gene redundancy
loss of function alleles may have no effect on phenotype
