Chapter 4 (GG)

Dominant mutant alleles

1) gain of function 2) dominant-negative mutations 3) haploinsuffieincy

At the molecular level, what is the explanation for why the flowers of the heterozygous four-o'-clock plant are pink instead of red?

50% of the functional protein is not enough to give a red color

Codominance

A condition in which neither of two alleles of a gene is dominant or recessive. The phenotype of the heterozygote is a mixture of the phenotypes of the homozygotes

Explain why a single gene knockout does not always have an effect on phenotype.

A single gene knockout does not have an effect due to gene redundancy and possible explanations

Haploinsufficiency

A situation in which the total level of a gene product (a particular protein) produced by the cell is about half of the normal level and that is not sufficient to permit the cell to function normally.

I^AI^B

Add either one of the sugars (N^Amine and galactose) at the many sites available

Huntington's disease (chorea)

Autosomal dominant A human genetic disease caused by a dominant allele Characterized by uncontrollable body movements and degeneration of the nervous system Usually fatal 10 to 20 years after the onset of symptoms Chorea: dance

I^O

Cannot add either terminal sugar, and thus possess only the H substance

Incomplete Dominance (partial dominance)

Carl Correns Situation in which one allele is not completely dominant over another allele The phenotype of the heterozygote is intermediate between that of the homozygous 1:2:1 phenotypical/genotypical ratio At microscopic level --> heterozygote is intermediate

Recessive lethal allele

If the heterozygous state is tolerated A pair of identical alleles that are both present in an organism that ultimately results in death of that organism

Dominant lethal allele

If the heterozygous state leads to death

Gene redundancy

Loss of function in a single gene has no phenotypic effect, but loss of function of two genes has an effect

Condition lethal alleles

May kill an organism only when certain environmental conditions prevail

At which level(s) is incomplete dominance more likely to be observed-the molecular, cellular, and/or organism level?

Molecular or cellular level

Temperature-sensitive (ts) lethals

Mutation that alter structure of the encoded protein so that it does not function correctly at the non permissive temperature (rapidly degraded)

Bombay Phenotype

Persons with the rare homozygous recessive genotype, hh, do not produce the precursor antigen H Genetically Type B Functionally Type O Can not make the complete H (A complete H antigen is used as the precursor for the A and B antigens) Form of hypostasis

A and B antigens

Sugar groups that are bound to lipids and protrude from the RBC membrane

Which allele is an example of a loss-of-function allele?

The i allele is a loss of function allele

Pleiotropy

The multiple effects of a single gene on the phenotype of an organism Reasons: 1. The expression of a single gene can affect cell function in more than one way 2. The gene may be expressed in different cell types in a multicellular organism 3. The gene may be expressed at different stages of development Ex: sickle-cell anemia

Gene knockout

Tn the case of diploid species The condition in which both copies of a gene have been altered to an inactive form

Incomplete penetrance

a dominant phenotype is not expressed even though an individual carries a dominant allele (ex: individual who carries the polydactyly allele but has a normal number of fingers and toes)

Recessive epistasis

a form of epistasis in which an individual must be homozygous for either recessive allele to mask a particular phenotype (9:3:4)

Sex-linked gene

a gene that is found on one of the two types of sex chromosomes

Hemizygous

a male has a single copy of an X-linked gene (ex: male mammal)

Sex-limited inheritance

a pattern of inheritance in which phenotypic expression is limited to one sex

Essential genes

absolutely required for survival absence of their protein product leads to a lethal phenotype 1/3 of all genes are essential

Gene modifier effect

an allele of one gene modifies the phenotypic outcome of the alleles of a different gene

Mutant allele

an allele that has been created by altering a wild-type allele by mutation rare in natural populations

Temperature-sensitive allele

an allele whose product is functional only at certain temperatures

Simple Mendelian Inheritance

an inheritance pattern involving a simple, dominant/recessive relationship that produces observed ratios in the offspring that readily obey Mendel's laws.

Dominant-negative mutations

change a protein such that the mutant protein acts hostile to the normal protein production of a protein that inhibits the function of a normal protein

Gain of function mutations

change the gene or the protein encoded by a gene so it gains a new or abnormal function an over expression of a gene or its protein product

Two different strains of sweet peas are true-breeding and have white flowers. When plants of these two strains are crossed, the F1 offspring all have purple flowers. This outcome is due to

complementation

I^B

encodes an enzyme that can add the terminal sugar galactose to the H substance

I^A

encodes an enzyme that can add the terminal sugar to N-Amine the H substance

The pattern where allelic variants of two different genes affect a single trait is called

gene redundancy (interaction)

Semilethal alleles

lethal alleles that kill some individuals but not all Environmental factors and other genes may help prevent the detrimental effects of semilethal genes

Multiple alleles

more than 2 alleles for the same gene found in a population Only can be studied in populations -An individual can only have two alleles for any given gene (ex: blood type)

Nonessential genes

not absolutely required for survival ex: eye/hair color

Lethal allele

one that has the potential to cause the death of an organism Result of mutations in essential genes Inherited in a recessive manner

Wild-type alleles

prevalent alleles in a natural population promotes the reproductive successes of organisms in their native environments

Sex influence inheritance

sex of individual influences expression of phenotype, not limited to one sex or the other some alleles are recessive in one sex and dominant in the opposite sex

In humans, a gene found in the X chromosome but not the Y chromosome is called a(n) ______ gene.

sex-linked

Age of onset

the age at which symptoms of a disease first appear

Epistasis

the alleles of one gene mask the phenotypic effects of the alleles of a different gene -Dominant (12:3:1) -Recessive (9:3:4) -Complement (9:7) -Duplicate Gene Action (15:1) -Suppression (13:3) -principles of segregation and random assortment do NOT apply

Norm of reaction

the effects of environmental variation on an individual's traits

X-linked inheritance

the inheritance of genes that are located on the X chromosome

Overdominance (heterozygote advantage)

the phenomenon in which a heterozygote is more vigorous than both of the corresponding homozygotes -Disease resistance -Homodimer formation -Variation in functional activity (ex: sickle cells)

Gene interaction

the phenomenon in which two or more different genes influence the outcome of a single trait

Complementation

two parents that express the same or similar recessive phenotypes produce offspring with a wild-type phenotype (9:7)

Genetic polymorphism

when two or more wild-type alleles occur in population; each allele is found at a frequency of 1% or higher.