Lecture 9 Flashcards
What are the 2 postulates are the basic principles 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 on the X chromosome
alleles
alternative forms of a gene
mutation
ultimate source of alleles
- knew phenotypes result from changes in functional activity of gene product
- eliminating enzyme function, changing relative enzyme efficiency, changing overall enzyme function
Wild-type allele
occurs most frequently on and usually, but not always dominant
loss-of-function mutation
- new phenotype results from change in activity
- mutation causes loss of wild-type function
gain-of-function mutations
- mutation enhances function of wild type
- quantity of gene product increases
neutral mutation
- no change to the phenotype
- no change to the evolutionary fitness of the organism
mutant allele
italic letter e
wild type allele
italic letter with + superscript
What are the alleles if no dominance exists
- italic uppercase letters and superscripts are used to denote alternative alleles
incomplete or partial dominance
- intermediate phenotype
- neither allele is dominant
- blend of the alleles
- pink
incomplete dominance in snapdragon
F1: pink flowers
F2: 1/4 red, 1/2 pink, 1/4 white
each genotype has its own phenotype
threshold effect
- normal phenotypic expression results
- certain level of gene product is attained
- in Tay-Sachs disease <50%
Codominace
- no dominance or recessiveness
- no incomplete or blending
- joint expression of both alleles in a heterozygote
- both alleles are expressed
- blood type
Codominance in humans MN blood
Genotype = Phenotype
LmLm = M
LmLn = MN
LnLn= N
1:2:1 ratio
multiple alleles
- three or more alleles of the same gene
- resulting mode of inheritance unique
- can only be studied in populations
what is an example of multiple alleles
Human ABO blood groups
- 3 alleles of a single gene responsible for ABO phenotypes
Thee blood type alleles
- IA
-IB
-i: recessive - A and B produce their respective antigens, i allele does not product antigens
- A and B are dominant to i
- A and B are co-dominant to each other
A and B antigens are…
carbohydrate groups bound to lipid groups on red blood cells
H substance
- one or two terminal sugars are added
- o blood types only have the H substance protruding from red blood cells
Bombay phenotype
- female found to be homozygous for FUT1 at the fucosyl transferase locus
- prevents her from producing H substance
- no substrate to make A or B antigen
- results functionally in type O
