Genetics

 1. What is Genetics?

Genetics is the study of how traits are inherited or passed between generations. 

Genes are small sections of a chromosome that are responsible for making 1 trait. Each person has at least 1 pair of genes (1 from mom, 1 from dad) for each trait.

2. Who is Gregor Mendel?

The father of Genetics! He experimented with sweet pea plants in the 1800s.

With this experiment, he made 3 laws and called them: The Laws of Heredity

3. What's an allele? 

Alleles are the different forms of the same gene(trait)

So, the TRAIT is having hair while the ALLELE is blonde color or brunette colored hair.

Dominant Alleles: The controlling allele, Usually shown with a capital letter (B)

Recessive Alleles: The hidden allele, Usually shown with a lowercase letter (b)

4. Law of Dominance

The Dominant allele will prevent the recessive allele from being expressed.

The Recessive allele will appear when it's paired with another recessive allele in the offspring.

5. Law of Segregation

Allele pairs must separate so that each gamete created during meiosis has only ONE allele from each pair allele coding for the same trait.

6. Law of Independent Assortment

During gamete formation (meiosis), alleles for different traits sort themselves independently of each other. 

7. Punnett Squares: Monohybrid

A Monohybrid Cross contains 4 boxes; 

a cross between two heterozygous individuals.

RATIO: 1: 2:1 Genotype & 3:1 phenotype ratio in the offspring. 

Probability: 75% or 3/4 dominant phenotype

8. Punnett Squares: Dihybrid

A Dihybrid Cross contains 16 Boxes; reveals two traits for both parents. 

A cross with two heterozygous individuals would reveal a RATIO of 9:3:3:1 phenotype in offspring

9. Patterns of Inheritance

Sex-Linked Traits

Traits (genes) located on the X chromosome can have effects on the offspring.    They can have the trait, carry the trait in their genes, or not have the trait at all. 

Multiple Alleles

Presence of TWO or more Alleles for a trait

For Example Eye Heterochromia in Cats

People also have this too!

Polygenic Inheritance

One trait is controlled by many genes. Genes may be on the same or different chromosomes. 

150 genes have now been identified as having a direct or indirect effect on skin color.

Codominance

Phenotypes of 

BOTH HOMOZYGOUS parents produce 

HETEROZYGOUS offspring where BOTH ALLELES are equally expressed/dominant

Example:

A White Cow with a Red Bull can create a Spotted White and Red Calf. 

Incomplete Dominance

The phenotype of a heterozygote is intermediate between two homozygous parents.

Neither allele is dominant! So it displayed as a mix

Here is a Homozygous Red flower with a 

Homozygous White Flower to create a 

Heterozygous Pink Flower

Pedigree

The record of descent of an organism. Helps determine inheritance in families and in animals!