Biol 114 Week 4: Beyond Mendelian Inheritance

Reciprocal Cross

crossing the opposite way (in this case, switching the traits of male and female parents). He mated females with white eyes with males with red eyes. The resulting F1 females had red eyes, BUT males had white eyes! Doesn’t seem to agree with Mendel.

Autosomal Inheritance

Inheritance of genes located on non-sex chromosomes

Sex-Linked Inheritance

Inheritance of genes located on the sex chromosomes

Multiple Allelism

The occurrence of more than two alleles for a locus in a population, even though only one occurs on each chromosome (2 on homologs in diploid cells). In Mendel’s world two alleles creates 3 genotypes and two phenotypes only.

Human Blood Types

Has 3 alleles at one locus (remember only 2 alleles per locus at a time can occur in a cell.

Beta-globin gene

in humans for making hemoglobin has over 500 different alleles that affect loads of variations having to do with living at various altitudes, different temperatures and resisting diseases

Incomplete dominance

Where a heterozygous genotype expresses an intermediate phenotype. Kind of like blending

Codominance

Both genotypes are expressed, not as a dilution of one (like incomplete) but as a combination of the two

Polygenetic effects

a single trait is affected by many genes with the effects being additive. Leads to continuous variation rather than an either/or situation

Pleiotropic effects

A single allele affects many traits.

Environmental effects

It’s important to distinguish how much of a trait is due to environmental pressures vs. how much is strictly genetic

Epigenetic effects

Environmental cues can cause certain genes to be turned on and off. These traits may last for generations, and then be switched back for generations. This gives some credence to Lamarck’s acquired characteristics