As mentioned previously it is lucky that Mendel chose to study pea plants and even more lucky the specific characteristics of pea plants he examined If he were to study more plants or more characteristics he would have seen exceptions to his principles This is because as we know now each chromosome carries many genes with each gene at a particular locus If genes are located on different chromosomes like we saw in the previous example then they assort independently which is also exactly what Mendel saw But what happens to genes that are located on the same chromosome Well they may be inherited together if they are located near each other These genes are therefore known as linked genes 4 Refer back to the ratios of phenotypes of the offspring generated from the testcross in question 3 on the previous page How would these ratios change if the genes for seed texture and plant height were linked Why Using the same plant let s examine two new traits shape of pollen grains and number of leaves To determine whether these traits assort independently or are linked a cross is performed between a homozygous plant with round pollen grains and two leaves PPLL and a homozygous plant that has long pollen grains and one leaf ppll Examine the diagram below depicting the crosses and then fill in the chart with the expected number of offspring for each phenotype shown P Generation F Generation Testcross Offspring of Testcross PPLL PpLI Meiosis would produce 4 types of gametes Observed Expected PL 991 X PpL1 X Pl 350 ppll ppll PL 334 A plant that is homozygous dominant for both traits is crossed with a plant that is homozygous recessive for both traits The resulting offspring are all heterozygous for both traits One of these offspring is then used in the testcross An offspring from the F generation is then crossed with a plant that is homozygous recessive for both traits pl 1025 pl Meiosis would produce 1 type of gamete 2 700 Total Offspring