Marc Pilon - Inheritence Flashcards
True breeding traits
When the observed form is the only form present for many generations.
Are there characteristics that can be irreversibly blended in succeeding generations?
No, and a recessive trait can reappear in succeeding generations.
Homozygous P generation, what is F2 generation?
P: RR x rr
F1: Rr x Rr
F2: Different combinations of alleles from each parent produces two different seed phenotypes. The seed phenotypes appear in a 3:1 ratio. RR, Rr, Rr, rr.
Test if a pea is homozygour or heterozygous
One pea is R_. Cross it with rr.
If F1 all show the dominant phenotype, R, the parental pea is RR.
If half the seeds in F1 show one phenotype, and the other half another phenotype, ratio 1:1, then the parental pea was heterozygous.
Dihybrid cross
A cross between identical double heterozygotes, like rY x rY.
Incomplete dominance
Example: the colour of eggplants.
True breeding plants that produce purple or white eggplants are crossed, making the F1 generation violet. Heterozygous plants produce violet fruit because the allele for purple is incompletely dominant over the allele for white.
When F1 plants are crossed, they produce purple, violet and white offspring in a 1:2:1 ratio.
Lethal alleles
Homozygous of one allele is lethal. Heterozygous is ok, for example yellow mice. Heterozygous of the other allele is the normal, black mouse.
Sex-linked traits
When the allele is on the sex chromosomes. For example colour blindness, where the allele is missing on the Y chromosome.
Environmental influence on gene expression
For example, colour of fur.
The temperature of the extremities is lower and allows expression of the black coat gene. The temperatures of most of the body is too high for the expression of the black coat gene, denaturating the protein.
Epistatic genes
When the expression of one gene is dependant on the expression of another gene. For example, the fur colour of dog, where the phenotype ratio is 9:4:3.
