Extensions Of Mendel’s Law Part 2 Flashcards
In large populations , more than one wild-type allele ma y occur—a p henomenon known as
Genetic polymorphism
prevalent alleles in a natural population as
wild-t yp e alleles
random mutations occur in population and alter preexistig alleles.
Mutant alleles
Because random mutations are more likel y to disrupt gene function,____ are often defective in their abilit ability to express a functional p rotein. Such _____ tend to be rare in natural populations. They are typically, but not alwa y s, inherited in a recessive fashion
mutant alleles
Phenylketonuria
Phenylalanine hydroxylase
Albinism
Tyrosinase
Tay-Sachs disease
Hexosaminidase A
Sandhoff disease
Hexosaminidase B
Cystic fibrosis
Chloride transporter
Lesch-Nyhan syndrome
Hypoxanthine-guanine phosphoribosyl transferase
One of three mechanisms accounts for most dominant mutant alleles:
a gain-of-function mutation
a dominant-negative mutation
haploinsufficiency .
chan g e the g ene or the p rotein encoded by a gene so that it gains a new or abnormal function
Gain-of-function mutations
For exam p le, a mutant g ene ma y be overex p ressed, thereb y p roducin g too much of the encoded p rotein.
Gain-of-function mutations
change protein such that the mutant protein acts antagonistically to the normal protein. In a heterozygote, the mutant p rotein counteracts the effects of the normal protein, thereby altering the phenotype.
Dominant-negative mutations
, the dominant mutant allele is a lossof-function allele.
Haploinsufficiency
is used to describe p atterns of inheritance in which a heteroz yg ote ( with one functional allele and one inactive allele ) exhibits an abnormal or disease phenotype
Haploinsufficiency
Haploinsufficiency
Another term used to describe the outcome of a trait is the degree to which the trait is expressed, or its______. In the case or polydactyly, the number or extra digits can vary. ror exam-ple, one mnaiviauar may nave an extra toe on only one root, wnereds a second individual may have extra digits on both the hands and feet.
expressivity
the range of phenotvpes is often due to two factors.
The______ may affect the outcome of the phenotype
One or more _____may also affect the phenotype.
environment
modifier genes
are those that are prevalent in a natural popu-lation.
Wild-type alleles
When a gene exists in two or more wild-type alleles, this
is
Genetic polymorphism
are often due to mutations that result in a reduction or loss of function of the encoded protein
Recessive alleles
Dominant mutant alleles are most commonly caused by
gain-or-function mutations, dominant-negative mutations, or haploinsufficiency
occurs when an allele that is expected to be expressed is not expressed
Incomplete penetrance
are those that are prevalent in a natural popu-lation. When a gene exists in two or more wild-type alleles, this is genetic
Wild-type alleles
A dramatic example of the relationship between environment and phenotype can be seen in the human genetic disease known as______
This autosomal recessive disease is caused by a defect in a gene that encodes the enzyme phenylalanine hydroxylase.
phenylketonuria (PKU)
refers to the effects of environmental variation on a phenotype. Specifi-cally, it is the phenotypic range seen in individuals with a particular genotype.
norm of reaction
Occurs When Two Alleles Produce an Intermediate Phenotype
Incomplete Dominance
Occurs When Heterozygotes
Have Greater Reproductive Success
Overdominance
Such heterozygotes may be more likely to survive and reproduce.
For example, a heterozygote may be larger, more disease-resistant, or better able to withstand harsh environmental conditions.
Overdominance
Alleles of the ABO Blood Group Can Be
Dominant, Recessive, or Codominant
. The i allele is recessive to both /^ and /”. A person who is homozygous ii has type___ blood and produces a relatively short oligosaccharide, which is called H antigen.
O
two alleles are both expressed in the heterozygous individual is called____. In this case, the /^ and /” alleles are codominant to each other.
codominance
The term _____refers to the phenomenon in which an allele is dominant in one sex but recessive in the opposite sex.
Therefore, sex _____ is a phenomenon of heterozygotes.
sex-influenced inheritance
The genes that govern ____traits are auto-somal, not on the X or Y chromosome.
sex-influenced
Some Traits Are Limited to One Sex
Sex-limited inheritance
Sex-limited traits are responsible for______, in which members of the opposite sex have different morphological features. This phenomenon is common among many animal species and is often striking among various species of birds in which the male has more ornate plumage than the female.
sexual dimorphism
• For___ traits such as scurs in cattle, heterozygous males and females have different phenotypes
sex-influenced
• are expressed in only one sex, thereby resulting in sexual dimorphism
Sex-limited traits
When the alleles of one gene mask the phenotypic effects of the alleles of another gene at a different locus, the phenomenon is called_____.
epistasis
