2. Dominant Genes
is expressed only when two copies of the gene are present.
is always expressed when present.
3. Recessive Genes
Opposed to dominant genes, is phenotypically expressed in the
homozygous state but has its expression masked in the presence of a
dominant gene.
is only expressed when no dominant genes are present.
4. How do we know of a trait is
dominant or recessive?
Traits are determined by the genes on the chromosomes. A gene is a
segment of DNA that determines a trait.
5. How do we know of a trait is
dominant or recessive?
Chromosomes come in homologous pairs, thus genes come in pairs.
Homologous pairs – matching genes – one from female parent and one
from male parent
6. How do we know if our traits are
recessive or dominant?
Based on parent’s genotype/phenotype
Could be:
Sex – linked Traits
Genes for these traits are located only on the X chromosome (NOT on the Y
chromosome). X linked alleles always show up in males whether dominant or
recessive because males have only one X chromosome
Incomplete dominance and Codominance
When one allele is NOT completely dominant over another (they blend) –
incomplete dominance
When both alleles are expressed – Codominance
