codominance and multiple alleles Flashcards
codominance meaning
in which both alleles are expressed in the phenotype
multiple alleles meaning
where there are more than two alleles, of which only two may be present at the loci of an individuals homologous chromosome
when does codominance occur?
where i stead of one allele being dominant and the other recessive both alleles of a gene are expressed in the phenotype
example of codominance
shorthorn cattle in which one allele codes for an enzyme that catalyses the formation of a different red pigment in hairs. the other allele codes for an altered enzyme that lacks this catalytic activity and so does not produce the pigment so hairs are white. as they are codominant 3 coast colours are found
what would happen if cattle are homozygous for the first allele
both alleles code for the enzyme and so pigment if produced. they have red hairs and a red coat
cattle that are homozygous for the second allele
no enzyme and hence no pigment is produced l. have white hairs and white coat
cattle whos alleles are in the heterozygous states
both coloured hairs are produced and the coast is therefore light red
what would happen if cattle with red coat is crossed with one with a white coat
the offspring has a light red roan coat
why can’t upper and lower case letters be used for alleles in codominance
this would imply that one was dominant for another. instead superscripts are used
example of multiple alleles
Blood groups. There are three alleles associated with the gene I which lead to the presence of different antigens on the cell surface membrane of red blood cells
which of the 3 alleles are dominant and recessive
A and B are codominant
O is recessive
how many of the three alleles can be present in an individual at any one time?
only two can be present in an individual at any one time as there are only two homologous chromosomes and therefore only two gene loci
what would in a cross between an individual of blood group O and one of blood group AB
rather than producing individuals of either of the parental blood groups it produces only individuals of the other two groups A and B
How may a cross between individuals of blood type A and B have children of shy for blood groups
both parents can be heterozygous a and o and b and o
