Chapter 9 - Patterns of Inheritance

AIM: Describe the rules that govern how traits are inherited.

A set of parents with the genotypes AABBEEFF and aabbeeff have offspring (F1) with the expected genotype of AaBbEeFf (male). One of these offspring are then crossed with another aabbeeff (female) individual. The genotypic ratio resulting is

1 AaBbEeFf : 1 AabbEeff : 1 aaBbeeFf : 1 aabbeeff

Draw a male cell showing the relevant chromosomes and the genes on those chromosomes.

I will put a more challenging mixed dependent/independent assortment problem on the quiz or test as extra credit like the one below. Everyone in the class is capable of doing this problem, it just requires extra studying. That is not to say there will not be an easier mixed problem…

Chapter 9 - Patterns of Inheritance

AIM: Describe the rules that govern how traits are inherited. If I were doing this problem, I think I would work backwards. I know the female gamete has to be abef. Therefore I know the male gametes because if a genotype of the offspring is AaBbEeff then the male gamete must have been ABEf, which fertilized the abef ovum. Using the same logic I would figure out the other male gametes: AbEF, aBef, and abeF. Now I need to figure out the arrangement of these alleles on the chromosomes. I know there will be fewer than four homolgous pairs since four pairs of homologous chromosomes would mean independent assortment (independent assortment would give far more male gametes…16). Looking at the four male gametes I notice that A is always with E, and a is always with e. Likewise I notice that b is always with F, and B is always with f. Therefore I would conclude that the arrangement would be two homolgous pairs of chromosomes. One pair (chromosome 1 let’s say) will have A and E together on one chromosome and a and e together on the other chromosome. The other pair would have b and F together on one chromosome and B and f together on the other chromosome.