Flashcards in Modifications Of Mendel Deck (14):
Define incomplete dominance and give example
Expression of heterozygote is intermediate between dominant homozygotes
• Four o’clock plant- red white pink
• Mendel’s peas- smooth/wrinkled
• Tay Sachs disease- homozygous recessive, hexoaminidase enzyme activity
Define codominance and give an example
Phenotypic effects are fully and simultaneously expressed in heterozygote
• Red white cow- spotted
• Sickle cell haemoglobin
Define multiple alleles
More than two alleles occurring at a locus
• Drosophila and human eyes
• ABO blood groups
How does the ABO blood group system work? What is involved other than multiple alleles?
A and B each produce different antigens
O produces none
A n-acetyl galactosamine
AB produces both
Complete and codominance
One gene affects many characteristics
• All blue eyed white cats are deaf
• Sickle cell haemoglobin is change in one base/amino acid- many detrimental effects- anaemia, heart failure, enlarged spleen
Define gene interaction
Several genes affect one character. Alleles at one locus can alter the phenotype produced by an allele at another locus
• Sex limitation effects in males- testosterone> secondary sex characteristics
• BRCA1 mutations- increase in breast cancer due to interaction btw cell division genes and oestrogen
• Mouse coat colours- at least 5 interacting loci
One allele preventing another at a different loci from expressing its effects
What ratio results from a dihybrid cross involving epistasis?
Eg. Albino mice
Define complementation and give an example
Two strains of an organism with different homozygous recessive mutations that produce the same phenotype
w1w1 W2W2 =white
W1W1 w2w2 =white
cross-> F1 W1w1 W2w2 =purple
F1 cross F1 -> F2 9purple:7white
What are complementation tests?
Show whether two alleles at a locus are involved or two/or more different loci
I.e. Cross two mutant homozygotes from different populations
If same locus, mutant F1 phenotypes shown
If different loci, parental phenotype shown- now het’s at both loci
Eg. Human deafness- many loci- outer ear, cilia of inner ear, nerve connections to brain. Two deaf parents can have hearing child.
What is a test cross?
Dominant individual crossed with homozygous recessive to determine if individual is homozygous or heterozygous
Phenotypic traits disappearing then reappearing later in the phylogenic tree
What is a back cross?
Crossing a hybrid with one of it’s parents/genetically similar individual
-> offspring with genetic identity closer to parents