Genetic Notes
I. General Information
A. Genetics – science of heredity (how we get and pass on traits)
B. Gregor Mendel – 1850
 Father of Genetics
C. Chromosomes
 composed of genes
 genes are a sequence of DNA that codes for 1 protein
 1 gene = 1 protein
- In some cases: 1 gene = 1 protein = 1 trait
- In most cases: genes/proteins work together to make 1 trait
II. Monohybrid Crosses: 1 gene = 1 trait
A. Alleles – a pair of genes that code for 1 protein
B. Genotype – the combination of alleles for a trait
– TT, Tt, tt
1. Dominant – allele whose trait is expressed
- T = tall
2. Recessive – allele whose trait is expressed only if the dominant allele is not present
- t = short
3. Homozygous – alleles are identical
- TT or tt
4. Heterozygous – alleles are different
- Tt
C. Phenotype – description of that trait (tall or short)
D. Segregation – occurs in meiosis
- process of separating the alleles into the different sex cells
- ½ will get 1 allele and the other ½ will get the other allele
- Ex: Parent Tt : ½ T and ½ t
TT: ½ T and ½ T ----- 1T
E. Punnet Square: Genotypic and Phenotypic ratios
- Predict all possible outcomes
- T = tall , t = short
- Parents T t ( ½ T and ½ t) X T t ( ½ T and ½ t)
Genotype
½T
Phenotype
½t
¼ TT
½T
¼ TT
¾ Tall
¼ Tt
2/4 Tt
½t
¼ Tt
¼ tt
¼ tt
¼ Short