Download Introduction to Genetics Notes

Introduction to Genetics Notes
GeneticsThe scientific study of heredity
What are Genes?
The chemical factors that determine traits
What are Alleles?
The different forms of a gene
Ex. Gene= plant height
Alleles= tall plants or short plants
19th centuryPeople wanted to understand how inheritance is passed on from generation to generation
Gregor MendelAustrian monk in charge of the monastery garden
- Worked with pea plants
Self- pollinationThe sperm cells in pollen fertilize the egg cells in the same flower
True-BreedingA plant is allowed to self-pollinate.
- This produces offspring identical to themselves.
Cross-pollinationProduces seeds that had 2 different plants as parents

7 Traits Mendel Studied
Cut away the pollen-bearing male parts and dusted the
pollen from another plant onto the flower
Why these 7 traits?
Each of these 7 traits had 2 contrasting characters (alleles)
Ex.
Seed
green seed
Color
yellow seed
Mendel’s Experiment
Mendel crossed plants with each of the 7 contrasting characters and studied their
offspring.
Parental
Generation
First Filial
Generation
-
To Mendel’s surprise, all of the offspring had the character of only one of the
parents (the other parent seemed to disappear)
1st conclusionBiological inheritance is determined by factors that are passed from 1 generation to the
next.
2nd conclusionPrinciple of Dominance: States that some alleles are dominant and others are recessive
DominantAn organism with a dominant allele for a particular from of a trait will always exhibit that
form of the trait.
RecessiveAn organism with a recessive allele will exhibit that form only when the dominant allele
for the trait is not present.
What happened to the recessive trait?
It was still there, but was masked by the dominant allele
Next,
Mendel crossed the F1 generation with itself and found that the traits controlled by the
recessive alleles had reappeared.
- This reappearance indicated that at some point the recessive allele separated from
the dominant allele.
SegregationThe separation of alleles during gamete formation
The recessive trait did not disappear!!!
When each F1 plant flowers and produces gametes, the 2 alleles segregate from each
other. So, each gamete carries only a single copy of each gene. Each F1 plant produces
2 types of gametes: a dominate allele (T) and a recessive allele (t)

Gene combinations that might result from a genetic cross
can be determined by drawing a Punnett square.

Punnet Squares – can be used to predict and compare the
genetic variations that will result from a cross

Cannot predict the precise outcome of an individual event
HomozygousOrganisms that have 2 identical alleles for a particular trait; a.k.a. Purebred
Ex. TT or tt
HeterozygousOrganisms that have 2 different alleles for the same trait; a.k.a. Hybrid
Ex. Tt
GenotypeGenetic makeup (letter combination)
Ex. TT, Tt or tt
PhenotypePhysical characteristic (what it looks like)
Ex. Tall or Short
How do you determine the genotype and phenotype of offspring?
Punnett squares are used to predict the outcomes of genetic crosses. The genotype and
phenotype are determined by looking at the result of the Punnett square.