1. Introduction to Genetics
Biology 30

2. What is GENETICS?
The science of heredity and variation in living organisms
A modern science that seeks to trace the patterns of inheritance

3. Genetic Terminology
Genetics – study of the inheritance of biological traits
Heredity – passing of traits from parents to offspring, through the use of genes.
Acquired Characteristics – developed based on the environment you live in. (Environmental dependent)

4. Genetic Terminology Chromosomes Genes Alleles
Produced from long strands of DNA
Long string of genes
Ex. Chromosomes 1-22 and the X,Y
Genes
Sections of a chromosome
Represented by a pair of letters designating a particular spot (loci) on a homologous pair of chromosomes
Units of instruction
Ex. Eye color
Alleles
Alternate forms of a particular gene
Have the same position of a pair of homologous chromosomes
Ex. Blue, Brown, or Green eye color

5. Genetic Terminology

6. Dominant – the allele that is expressed when present with another
Recessive – the allele that is masked when present with a dominant gene; is expressed when individuals are homozygous for 2 recessive genes.
Genotype – the genetic make-up of an individual; TT, Tt, or tt
Phenotype – the physical expression or appearance of an individual; TT tall, Tt tall, tt short

7. Homozygous – offspring inheriting identical alleles (TT – tall or tt – short)
Heterozygous – offspring inheriting different alleles (Tt – tall)
Hybrid – an individual which is heterozygous for one or more alleles
Monohybrid – studying a cross involving only one characteristic or allele
Dihybrid – studying a cross involving two characteristics or alleles

8. Parent generation (P1) – the parents involved in a cross
1st Filial Generation (F1) – the offspring from the P1
2nd Filial Generation (F2) – the second set of offspring extending from the P1
(ie, the children of F1)

9. Gregor Mendel Was a monk in the 1800’s who studied pea plants.
He crossed different types of peas to see what kind of offspring they yielded.

12. Review of Mendel’s Theories
Factors occur in pairs (genes)
As humans we have two “versions/alleles” of every gene
Dominant vs. Recessive
– dominant gene masks recessive gene
Law of segregation
– during sex cell formation these paired factors (genes) separate/segregate into separate sex cells

13. Pure Breeding vs. Hybrids
– pure breeding contains two genes that are identical (homozygous TT or tt) hybrids are heterozygous (Tt)
Law of Independent Assortment
– chromosomes separate independently of each other

14. Gamete Formation Represent traits using the same letter
i.e., earlobes
Free = E; attached = e
Gametes only contain one of each kind of gene
i.e., Ee parent makes gametes with either E or e

15. Single Trait Inheritance (monohybrid Crosses)
Comparing a single trait in two reproducing organisms
Use a Punnett square – a chart that shows potential gametes and offspring frequencies (ratios, probabilities)

16. Problem:
A homozygous round seed is crossed with a homozygous wrinkled seed. What are the genotype and phenotype frequencies in the F1?
b) cross 2 F1’s