1. Gregor Mendel – “Father of Genetics”
Genetics Review
Gregor Mendel – “Father of Genetics”

2. Genetics Vocabulary:
Heredity – the passing of traits from parent to offspring
Genetics– the study of heredity
Dominant – the expressed form of a trait; ex: T
Recessive – the trait that is not expressed; ex: t
Homozygous – when the two alleles of a trait are the same; ex: TT, tt
Heterozygous – when the two alleles of a trait are different; ex: Tt
Genotype – the set of alleles for a trait; ex: TT, Tt, tt
Phenotype – the physical appearance of a trait; ex: tall or short

3. Punnett Squares – a diagram that predicts the outcome of a cross
Monohybrid Cross – a cross between individuals that
involves one pair of contrasting traits
Dihybrid cross - a cross between individuals that involves
two pairs of contrasting traits
= RY, Ry, rY, ry

4. Example of a Monohybrid Cross Example of a Dihybrid Cross
Phenotypic Ratio: 9:3:3:1
Phenotypic Ratio: 9:3:3:1

5. Pedigree - a diagram that shows a trait inherited over several
Male
Female

6. Complex Patterns of Heredity
Sex-linked Disorders – occurs mainly in males b/c the mother
usually donates the recessive allele;
use the X and Y chromosomes to set
your punnette square
Polygenic Traits – traits influenced by several genes
Multiple Alleles – ex: blood types AB, A, B, & O have three
alleles (A, B, O)

7. Complex Patterns of Heredity
Complete Dominance – dominant trait is expressed as long as
on of the alleles is present
ex: BB (black) Bb (black) bb (white)
Codominant – two dominant traits are expressed at the same
time
ex: BB (black) BW (black & white) WW (white)
Incomplete Dominance - a trait that is intermediate between
the two parents
ex: BB (black) Bb (gray) bb (white)

8. Genetic Disorders – caused by a mutated gene that in turn makes a
defective protein
Example of genetic disorders:
sickle cell anemia – recessive disorder; RBC’s are deformed
hemophilia – sex linked disorder (X-chromosome); blood doesn’t clot
properly
colorblindness – sex-linked (X-chromosome)
Genetic counseling – identifies risks & counsels parents through a variety
of different tests
Gene technology (or gene therapy) – replacement of a defect gene with a
healthy one