Chapter 4: Flashcards
Two postulates that are the possible of gene transmission
- Genes are present on homologous chromosomes
- Chromosomes segregate and assort independently
Gene interaction
Single phenotype is affected by more than one set of genes
X-Linkage
genes that are present in the X chromosome
Alleles
alternative forms of a gene
Mutation
Ultimate source of alleles
Note: new phenotype result from changes in functional activity if gene product
-Elimination enzyme function
-Changing relative enzyme efficiency
-Changing overall enzyme function
Wild-type alleles
Occurs most frequently in nature and is usually (not always) dominant
Due to natural selection
Loss of function Mutations
-New phenotype results from change in activity
-Mutation causes loss of wild-type function
Gan-of function mutations
-Mutation enhances function of will type
-Quantity of gene product increases
Neutral mutations
-No change to the phenotype
-No change to the evolutionary fitness of the organism
DO MORE RESEARCH ON THIS: Adding or moving the amino acid is dangerous
Dominant alleles are indicated by
-an italoc uppercase letter of uppercase case
Recessive alleles are indicated by
an italic lowercase letter, or an italic letter or group of letters
Mutant alleles are indicated by
an italic letter
Wild type alleles are indicated by
italic letter plus superscript + (e^+)
Incomplete or partial dominance
Intermediate phenotype
Niether alle is dominant
Example of dominance in snapdragon
Red snapdragon is crossed with whote snapdragon
F1 offspring: pink flowers
F2 generation: 1/4 red, 1/2 pink, 1/4 white
-Phenotypic and genotypic ratios are the same
Each genotype has its own phenotype
Incomplete dominance in humans example
Tay-Sachs disease
Threshold Effect
Normal phenotypic expression results
Certain level (usually 50% or less) of gene product is attained
In Tay-Sach’s disease, less than a 50 percent threshold
Codominance
-No dominance or recessiveness
-No incomplete or blending
-Joint expression of both alleles in a heterozygote
Multiple alleles
-Three or more alleles of the same gene
-resulting mode of inheritance unique
-Can only be studied in populations
Example of Multiple alleles
Human ABO blood groups
-example of muliple alleles
-A and B antigens present on surface of red blood cells
-Three alleles of a single gene responsible for ABO phenotypes
A and B antigens
CArbohydrate groups bound to lipid groups on red blood cells
H substance
-One or two terminal sugars are added
-O blood types (ii) only have the H substance protruding from the red blood cells
Essential genes
Absolutely required for survival
-Mustations can be tolerated if heterozygous
Why can mutations (if heterozygous) of essential genes be tolerated?
One type of allele is sufficient for survivial
Homozygous recessive will not survive
Recessive lethal allele
Mutaion of essential genes behaves as a recessive lethal alleleq
Lethal Allele
Has the potential to cause death of organism
-alleles are a result of mitations in essential genes
-inherited in a recessive manner
-
Dominant lethal allele + provide an example
-Presence of one copy of allele results in death
Ex. Huntigton’s disease
Huntigton’s disease
Dominant autosomal allele H
Onset of disease in heterozygous delayed until adulthood
Characterized by progressive degeneration o f nervous system, dementia, and early death
Agouti gene in mice (coat color)
Agouti allele A
Mutant yellow allele A^y
Mutant Allele (A^y)
Behvaes dominantly to normal allele to control coat color
Behaves as homozygous recessive lethal allele
Pleiotropy
Expression of single gene has multiple phenotypic effects
Example Marfan syndrome
Porphyria Variegata
Sex-limited inheritance
Expression of specific phenotype is limited to one sex
Sex-influenced inheritance
Sex of individual influences expression of the phenotype
Not limited to one sex or the other
Penetrance
Percentage of expression of the mutant genotype in a population
Expressivity
-Range of expression of mutant phenotype
-REsult of genetic background differences or environmental effects
Genetic background: Position effect
-The physical location of gene influences expression
-Translocation or inversion events modify the expression
-Gene relocated to condensed or genetically inert chromosome (called heterochromatin)
Conditional Mutations
Ideal temperatures for animals
Example: Darker fur on cooler areas of body (tail, feet, ears)
enzymes loose catalytic function at higher temps
Nutritional mutations in genetics
prevent ssynthesis of nutrient molecules in microbes
Phenotype may be expressed depending on diet
Example Phenylketonuria: loss of an enzyme to metabolize amino acid called phenylalanine, severe issues unless low Phe diet
