1. Introduction to Genetics
Genetics is the study of heredity
The inheritance of traits

2. A trait is a characteristic passed from parent to offspring
A trait is a characteristic passed from parent to offspring. Some human traits include:

3. In the 1800’s Gregor Mendel used pea plants to study the inheritance of traits
A trait is a specific characteristic that varies between one individual in a population to another
When fertilization takes place it, produces a new cell
Pea plants self fertilize so they inherit their own characteristics
These are true breeding and produce purebred offspring

4. Mendel removed the male parts of the pea flowers and made controlled crosses between plants with different traits
This is called cross pollination

5. Cross pollination produces seeds that have two different parents
Mendel studied seven traits in the pea plants
He chose these traits because they show only one of the two contrasting characteristics

6. The different forms of a gene that produce traits
Are called alleles
The first cross breeding of different parent plants creates a hybrid filial
Also called F1 generation
Crosses between parents with different traits are called hybrids
When Mendel crossed true breeding tall pea plants with true breeding short plants he created a hybrid

7. Mendel crossed tall and short pea plants to create a hybrid
All of the offspring in the F1 generation were tall because the allele for the tall trait was dominant over the allele for the short trait
Did the allele for the recessive trait disappear?
When he let the F1 generation self pollinate the recessive trait re-appeared
At some point, the recessive allele segregated from the dominant allele

8. When Mendel repeated other crosses he obtained similar results

9. Which traits for the pea color and parakeet color are recessive?
How do you know?

10. Today these chemical factors that determine traits are called genes
Mendel realized that the principal of probability can be used to predict the outcome of genetic crosses
Mendel concluded that traits are inherited through the passing of factors from parents to offspring
Today these chemical factors that determine traits are called genes
The principal of dominance states that some alleles are dominant and some are recessive

11. The capital letter T represents the dominant allele
This chart shows the segregation of alleles during a cross between two hybrid parents
The capital letter T represents the dominant allele
The lower case letter t represents the recessive allele
Punnett squares can be used to predict and compare genetic variations that may result from a cross
Shows that the genes for traits sort independently

12. Phenotype and Genotype
Organisms that have two identical alleles for a trait are called homozygous (TT), or (tt)
These are known as purebreds
(TT) is homozygous dominant
(tt) is homozygous recessive
Organisms that have two different alleles for the same trait are heterozygous (Tt)
These are known as hybrids
An organisms physical characteristics is called the phenotype
The genetic makeup discussed above is called the genotype

13. A one factor Punnett square (monohybrid cross) follows one gene during a cross

14. A two factor Punnett square (dihybrid cross) follows two different genes from one generation to the next
Mendel found that traits would follow the laws of probability and show independent assortment
Found that different traits can segregate independently during fertilization

15. Intermediate inheritance
Purely dominant and recessive traits are rare in nature
Many genes show an intermediate inheritance
Incomplete dominance is when neither allele dominates over the other
Shows a blending of the two traits

16. When different dominant traits are crossed and both are present in the offspring this is co-dominance
A cross between a black chicken (BB) and a white rooster (WW) X
Producing a speckled offspring (BW)

17. a second type of co-dominance is human blood type
Like type AB blood

18. When two or more alleles for a trait exist in a population the gene has multiple alleles
Fur color in rabbits has multiple alleles
Blood type in humans also has multiple alleles

19. Traits controlled by two or more genes are called polygenetic traits
Human skin color is a polygenetic trait, over 4 genes are involved in determining skin color
Eye color is also polygenetic

20. The environment can also have an effect on gene expression
Seasonal coat color in foxes and seasonal wing coloration on butterflies
Hydrangea flower color to soil pH, goby fish change sex in male dominated populations are all examples of gene expression responding to environmental conditions

21. He used fruit flies called drosophila melanogaster
Another scientist that tried to advance the study of genetics was Thomas Morgan
He used fruit flies called drosophila melanogaster
They produced large numbers of offspring in a very short time
Only have 8 chromosomes to track
He found that Mendel’s principals also applied to the flies
The basics of Mendelian genetics can also apply to human genetics

22. The farther apart two genes are on a chromosome, the more likely they are separated by a crossover
The frequency of crossing-over between genes can be used to construct genetic maps