BIO340 Activity #4: 3-Point Cross, Gene Order and Mapping
I. Determining single-crossovers , double-crossovers and gene order.
We want to map the distance between genes for:
leaf color ,
leaf texture , and
plant fertility .
Your mapping cross is like a test cross. One parent is heterozygous for all
genes while the other parent is
homozygous recessive for all genes .
Gene order is not yet determined.
Below, write the genotypes of the
mapping cross individual and the cryptic individual:
Table 1: Progeny from Mapping Cross
Phenotype Frequency Phenotype Frequency
1. Green, rough, normal 95 5. Green, smooth, normal 900
2. Yellow, rough, normal 50 6. Yellow, smooth, normal 5
3. Green, rough, variable 5 7. Green, smooth, variable 50
4. Yellow, rough, variable 900 8. Yellow, smooth, variable 95
Based on these results, are the genes linked or not?
How would the phenotypic frequencies look if the genes were not linked?
Which two numbered phenotypes in Table 1, represent offspring of the parental types?
Using slash notation, the parental type offspring have genotypes:
The actual chromosomal configuration of the mapping individual in the cross must have been
Which two numbered phenotypes in Table 1, represent offspring from DCOs?
Using slash notation, the DCO offspring have genotypes:
Comparing the mapping individual’s chromosome configuration with the chromosome
configuration of the DCOs, you can tell which gene is in the center of the other two based upon
which gene “switched sides” from parental type chromosomes to DCO type chromosomes?
Which gene is in the middle?
