Test cross, Co-dominance and Multiple alleles Flashcards
why is a test cross used?
-to determine the genotype of an individual with dominant phenotype but an unkown genotype
what do you always cross with in a test cross?
-the recessive
what is the genotype of the parent if any of their offspring show the recessive phenotype?
-one of them has to be heterozygous
what is co-dominance?
-two alleles at a particular gene locus are different but neither has a dominant effect over the other
what is the result of co dominance in the phenotypes of individuals?
-the phenotypes of heterozygous and homozygous dominant are different when they would usually be the same
what is the ratio when two heterozygous co dominant parents are crossed?
-1:2:1
can one gene have more than two alleles?
-yes
what is an example of inheritance with multiple alleles? how many does it have?
-human blood group
-4 alleles A B AB O
which blood group always recessive?
- O
if a parent with blood group A and another with B have offspring, what is the percent chance that they will be blood group A, B, AB or O?
-all 25% each
what is the term used to describe allele combinations that cause the genotype to be unviable?
-lethal alleles
what do lethal alleles cause?
-typically the death of an organism
what are the two types of lethal alleles?
-recessive lethal alleles and dominant
when do recessive lethal alleles cause death? what is the effect of an organism having one recessive lethal allele?
-when two homozygous alleles are inherited
-if an organism carries only one of these recessive alleles then it will not cause death it has to have both copies recessive
when do dominant lethal alleles cause death?
-these cause death even when one copy is present e.g. when the organism is heterozygous
what is an example of a condition which is cause by inheritance of dominant lethal alleles?
-Huntington’s disease
