midterm material Flashcards
What is a “locus”?
Specific place on a chromosome occupied by a gene
Describe the 2 types of recessive mutations
Null/Amorphic alleles produce a non-functional protein OR no protein at all.
Hypomorphic alleles produce a poorly functioning protein OR reduced amounts of a normally functioning protein.
Describe the 2 types of dominant mutations
Hypermorphic alleles cause negative phenotypic consequences due to over-production of a normal protein OR production of a protein with increased activity levels.
Neomorphic alleles cause negative phenotypic consequences due to the presence of an altered protein that has a new function OR an altered protein that interferes with the wildtype protein.
What is Incomplete Dominance?
The heterozygous is an intermediate between the homozygous phenotypes.
What is Co-dominance?
The heterozygous exhibits phenotypes of both of the homozygotes.
What is an allelic series?
An allelic series describes the dominance hierarchy of multiple alleles.
What is a wildtype allele?
A functional enzyme or other protein is produced.
Sometimes wildtype is used to refer to the most common genotype or phenotype found in a population.
Name the term:
Half as much protein is synthesized but this is not enough to achieve the wildtype phenotype. Give an example.
Haploinsufficiency, example Manx cats
T or F:
A dominant allele can be a loss of function allele.
True.
What is the difference between dominant lethal alleles and recessive lethal alleles? Give examples.
Dominant lethal alleles can be expressed in both the homozygote dominant and the heterzygote. eg. Huntington’s.
Recessive lethal alleles are only expressed in the homozygote recessive. eg. Tay Sachs.
Name the term:
The proportion of individuals that have a particular genotype and express the expected phenotype.
Penetrance (variation in the population).
Name the term:
The degree to which a phenotype is expressed.
Expressivity (variation in the individual).
Name the 4 environmental factors that can affect phenotypic expression.
Age, sex, temperature, chemicals.
What is the “norm of reaction”?
The range of phenotypes expressed by a single genotype under different environmental conditions.
Describe the himalayan allele in rabbits.
The himalayan allele produces dark fur at the extremities, as the enzyme necessary for pigment production is inactive at high temperatures.
What is a phenocopy? Give an example.
A phenocopy is a change in phenotype caused by the environment that mimics the effects of a gene mutation.
The chemical thalidomide can produce a phenocopy of a rare trait called phocomelia.
Name the term:
The inheritance pattern of one trait will not affect the inheritance pattern of another trait.
Mendel’s Law of Independent Assortment
What is Complementation?
Complementation occurs when two strains of an organism with different homozygous recessive mutations that produce the same phenotype produce offspring with the wildtype phenotype.
T or F:
Complementation only occurs if the mutations are in different genes.
True. The other genome supplies the wildtype allele to complement the mutated allele.
What is a Heterogenous Trait?
A mutation in any of a number of genes results in the same phenotype.
What is Epistasis? Which is the epistatic gene and which is hypostatic?
Epistasis is the masking of the expression of one gene by another, where no new phenotypes are created.
The epistatic gene does the masking while the hypostatic gene is masked.
Compare “dominant epistasis” and “recessive epistasis”.
In dominant epistasis one dominant allele at one gene masks expression from another gene whereas in recessive epistasis homozygous recessive alleles at one gene pair mask expression from the other gene. In both cases only 3 distinct phenotypes are produced.
What is Pleiotropy? Give an example.
A single gene can cause a number of distinct and seemingly unrelated phenotypic effects.
Sickle cell and cystic fibrosis occur at the same gene.
T or F:
Inbreeding increases the frequency of homozygotes and decreases the frequency of heterozygotes.
True.
What is “heterosis”?
Heterosis, AKA hybrid vigor, occurs when two different inbred lines are crossed and the hybrid is heterozygous for many genes.
T or F:
The X and Y chromosomes pair during meiosis even though they are not homologous.
True.
What is an Autopolyploid?
A polyploid organism where are the chromosome sets are identical, and the chromosomes are all derived from the same species.
What is an Allopolyploid?
A polyploid organism that is the cross between 2 or more species.
What is the main issue with polyploidy, and what is the solution?
Many polyploids are sterile because their multiple sets of chromosomes separate irregularly. This is solved by doubling the number of chromosomes.
What is Aneuploidy?
Occurs when a diploid genome either lacks a chromosome or has an extra one.
In humans autosomal monosomies are lost during pregnancy. Name the 3 autosomal trisomies that are live births.
Down Syndrome (trisomy 21) Patau Syndrome (trisomy 13) Edwards Syndrome (trisomy 18)
XXY is known as?
Klinefelter Syndrome
XO is known as?
Turner Syndrome
