1. Basic Elements of Genetics
By Jane Horlings

2. Genetics The alternate forms of a gene are called alleles
Alleles are denoted by a letter or letters; dominant genes are typically denoted by a capital letter, recessive genes with a lower case letter

3. Genetics
If cells have the same allele for a certain trait, they are homozygous
We can say characterize this as homozygous dominant or homozygous recessive

4. Genetics
If cells have different alleles for the trait, it is termed heterozygous
A heterozygote would have one dominant and one recessive allele
A plant might have one allele for yellow seeds and one allele for green seeds

5. Genetics
Heterozygotes carry two different alleles (e.g. Hh); homozygotes carry identical alleles (HH or hh)
Heterozygotes have a recessive and a dominant allele for a particular characteristic (Hh)

6. Genetics We refer to the genetic makeup of an organism as its genotype
The genotype is what is in the genes
The physical appearance is the phenotype
The phenotype is what is “seen”

7. Genetics
The genotype of these peas might be Ww (one dominant gene, smooth, and one recessive gene, wrinkled)
The phenotype is smooth

8. Genetics
The phenotype of an individual does not always reveal its genotype
Heterozygotes (e.g. Hh) show the dominant trait H; the recessive trait h is masked
The phenotype of the homozygous dominant (HH) and the heterozygote (Hh) is typically identical

9. Genetics