For this modeling activity, assume that your species reproduces sexually. This assumption implies that it inherits half of its chromosomes from its mother and half from its father. Recall that in sexual reproduction, individuals inherit homologous pairs of chromosomes—one from the father and one from the mother. This arrangement allows for two alleles for every gene. The alleles can be dominant or recessive. You will model three traits controlled by three gene types on homologous chromosomes. Your genes should have these patterns of inheritance: Trait 1: Simple dominant/recessive inheritance

Example: In pea plants, YY and Yy genotypes will yield yellow pea pods, but inherited yy will yield green pea pods.

Trait 2: Co-dominance

Co-dominance occurs when there’s more than one dominant allele and they express equally.

Example: Human blood type is co-dominant. IA (type A blood), IB (type B), and i (O blood) are controlled by A and B dominant alleles. If a person inherits A and B alleles, they’ll have AB blood. O blood is caused by two recessive alleles.

Trait 3: Incomplete dominance

Incomplete dominance occurs when there is more than one dominant gene, but the expression of both genes creates a blending of traits.

Example: RR = red flowers, WW = white flower, but RW = pink flowers.

Come up with your three traits and the possible inherited phenotypes. Here’s an example:

Trait Phenotype 1 Phenotype 2 Phenotype 3 Phenotype 4
Seed Color
(simple/dominant recessive) Yy and YY
(yellow seeds) yy (green seeds) N/A N/A
Flower Color
(co-dominance) IRIR and IRi = red flowers IWIW and IWi = white flowers IWIR = red/white speckled ii = yellow flowers
Pod Shape
(incomplete dominance) PP = long, balloon-shaped pods FF = flat, narrow pods PF = long, flat pods N/A
To get started, think about the traits your species needs to help it survive in its environment. Come up with variations of these traits. You can include neutral traits (variations that won’t affect the organism’s survival), and beneficial traits (variations that would give the organism a better chance for survival). You can even include harmful genes or genes that could cause genetic diseases. Fill in the chart with the traits you chose and the possible inherited phenotypes.