Genetics Ch. 4

Gene interaction

ways genes interact to influence a phenotype
may be more than two alleles for given locus within a population
dominance of one allele over another may not be complete
two or more genes may affect a single trait

Haplosufficient

one copy of it is enough for normal function

Haploinsufficient

one copy is not enough for normal function

gain of function

gene product acquires a new function or express increased wild type activity

Loss of function

there is a significant decrease or complete loss of functional gene product

null mutation/ amorphic mutation

loss of function mutations that produce no functional gene product, lethal when homozygous

leaky mutations or hypomorphic mutations

loss of function mutations that result in a partial loss of function

Dominant Negative mutations

dominant due to loss of function of multi metric protein due to an amino acid change in one subunit
spoiler effect on protein

Hypermorphic

mutation that produces more gene activity than normal
gain of function mutation

neomorphic

gain of function
mutations acquire novel gene activities not found in the wild type

incomplete dominance

heterozygous individuals display intermediate phenotypes between homozygous type

Codominance

leads to heterozygotes with a different phenotype than that of either homozygote

ABO alleles

4 different types

A blood type / B blood type

has A antigen on surface/ has B antigen on surface

Blood group antigens

glycolipids with lipid portion anchored in the red blood cell membrane

lethal mutations

inherited as recessive alleles, can be detected as distortions in segregation ratios caused by one or more missing classes of progeny

Sex- limited traits

sex-limited gene expression is a pattern of expression limited to one sex or the other

Sex influenced traits

the phenotype corresponding to a particular genotype differs depending on sex of the organism

Incomplete penetrance and variable expressivity

complicate interpretation of genotypic phenotypic ratios

variable expressivity

individuals who carry the alleles for a trait show a phenotype but to a varying degree of severity

Pleiotropy

alteration of multiple distinct traits by a mutation in a single gene

Sickle cell disease

autosomal recessive condition caused by mutation in the B-globin gene

Epistasis

alleles of one gene modify or prevent expression of alleles of another gene
minimum of two genes required

absence of epistasis

9:3:3:1 ratio is seen

complementary gene interaction

when two genes work in tandem to produce single gene product

Redundant system

a dominant allele at either locus gives rise to a wild type phenotype
duplicate gene action

Dominant interaction

9:6:1 dihybrid ratio

Recessive Epistasis

9:3:4 Ratio

Dominant Epistasis

12:3:1 ratio

Dominant suppression

13:3 ratio

Complementation analysis

distinguishes mutations in the same gene from mutations in different genes
occurs when the mutations in the parents affect different genes

Complementation Testing

two pure breeding organisms with similar mutant phenotypes are mated

Complementation Analysis

multiple crosses are performed among numerous pure breeding mutants to try to determine how many different genes contribute to a phenotype

Which of the following classes of mutations is generally recessive

...

Crossing true-breeding strains of petunia (red and white) produces an F1 with only pink flowers. If the F1 are selfed, what will the phenotype ratios in F2 be?

� red : � pink : � white

How many different phenotypes are possible in a one gene/three allele system that displays codominance to each other?

six

Which of the following is the most likely example of codominance?

A pure-breeding plant with red flowers is crossed to a pure-breeding plant with white flowers. All their progeny have flowers with some red patches and some white patches.

The color dilution gene in horses is an example of incomplete dominance.

true

The Beadle and Tatum experiments were based on all of the following assumptions except that _______.

two strains of auxotrophic Neurospora that grow on minimal medium supplemented with biotin have mutations in the same gene

n their first round of screening, Beadle and Tatum plated spores on minimal medium. The purpose of this screen was to _______.

determine whether any auxotrophic mutants had been generated

Which of the following can be inferred from the Beadle and Tatum experiments?

For a mutation resulting in the production of a defective enzyme involved in a biosynthetic pathway, the compound preceding the corresponding step will accumulate.

All of the following are required in complementation testing in yeast except _______

an auxotrophic organism

Two yeast strains are identified. As the result of different mutations, each in a separate gene, each strain is auxotrophic for compound Y, a compound required for growth. Which of the following results would be expected in a complementation test involvin

Cells would grow without supplementing compound Y.

For two mutations, each occurring in a separate gene, mutants can complement each other only if the genes are not involved in the same pathway.

False

_______________ indicates that less than 100% of individuals with a mutant genotype have the mutant phenotype.

incomplete penetrance

______________ indicates that the severity of a mutant phenotype differs among individuals with the same mutant genotype.

variable expressivity

A recessive allele that results in a complete loss of gene function is known as which of the following types of mutation?

Amorphic

Consider a recessive mutation that results in a complete loss of gene function. If heterozygous individuals (mutant/wild-type) are phenotypically wild-type, then the wild-type allele would be described as being _______.

haplosufficient

What types of mutants commonly result from regulatory mutations that increase the rate of transcription of a gene?

hypermorphic

If two alleles of a gene (T1 & T2) are incompletely dominant, then selfing individuals that are heterozygous for these two alleles will produce what phenotypic ratios among the progeny?

1:2:1

What type of molecule on the surface of red blood cells is responsible for the determination of ABO blood type?

Glycolipid

In 1905, Lucien Cuenot observed that crosses between two yellow mice consistently produced progeny ratios of two yellow : one agouti (wild-type). What is the explanation for the observed 2:1 phenotype ratio?

The yellow allele is a recessive lethal.

What is the name given to the phenomenon in which some individuals with a particular genotype fail to display the corresponding phenotype?

Incomplete penetrance

What is meant by variable expressivity in genetics?

A single genotype produces a range of phenotypes that differ in the degree or magnitude of expression of the particular trait specified by the gene.

In complementary gene interactions, two genes work in tandem to produce a particular phenotype. Functional copies of both genes are required to produce the phenotype. What phenotypic ratios would be expected among the F2 progeny of a dihybrid cross involv

9:7

In genetic complementation testing, crosses are performed between pure-breeding strains for recessive mutations that confer the same mutant phenotype. If the two mutations are in different genes, then what phenotypic ratios would be expected among the pro

All of the F1 progeny would be wild-type.