Lecture 3 - Punnet Squares & Test Crosses

Question 1

when crossing sex chromosomes, what is the expected ratio

Answer 1

1:1 or 50/50

Question 2

a punnet square is helpful with…

Answer 2

a simple way of visualizing the results of segregation during gamete formation as well as the random union of alleles during fertilization

Question 3

what is a test cross used for?

Answer 3

to ensure an organism is homozygous or of true breeding

Question 4

how is a test cross run?

Answer 4

1. label genotype under investigation as R_ (the underscore)
2. breed organism with another which is homozygous recessive
3. Results –> either the offspring will all be Rr and show dominant phenotype
   or
   the offspring will be 50% dominant trait and 50% recessive trait

Question 5

why can’t we let an organism self when conducting test cross?

Answer 5

because not all organisms are able to do this (animals)