Genetics

Genetics.....

Mendelian Genetics 6.3 - 6.5

The groundwork of our understanding of genetics came from the Austrian monk known as Gregor Mendel in the mid 1800's.

He was fascinated with pea plants and used them in his experiments because they reproduced quickly.

He crossed two different color pea plants which he thought were "purebred" and observed their offspring traits (characteristics passed from parent to offspring).




He concluded that there was something causing the pea plant to appear different than the others.

This same concept can be used for our genetic makeup....

We have different forms of genes in our chromosomes called Alleles represented by letters. 



The terms Dominant (Strong allele) and Recessive (Weak allele) are used to determine the outcome of certain traits.

Dominant: Expressed when at least one strong allele is present and is most commonly seen in a population.

Recessive: Only expressed when two identical weak alleles are present.

Homozygous vs Heterozygous

Using this information we are able to determine the Genotype (Genetic makeup=GG, gg, or Gg) and the Phenotype (Physical characteristic=brown, tall, round etc....)

Tutorial on Punnett Squares 

Monohybrid Cross: When one trait is used for example one letter T (TT x tt) or(Tt x tt) or (tt x tt). The capital letter is written first.



Practice
More Practice

Dihybrid Cross

Laws of Genetics:

Law of Independent Assortment - alleles separate independently from each other during meiosis. 

What does this mean? 

This means one trait can result independently of another trait.

Tall is dominant to short plant. Green pea color is dominant to yellow.

Can the plant come out Short with Green peas? or Tall with yellow?

Dihybrid Cross: When two traits are used for example two letters R and Y. 
Male RrYy x Female RrYy (Tall & Green).

Possible Combos: 
Male:
Female:



Lets try some Punnett Square Problems....

Brown eyes (B) are dominant to blue eyes (b). Tall height (G) is dominant to short (g).

What are the chances of a child being born with blue eyes and tall in height.

Hunger Games
Practice 1
Practice 2
Dihybrid Cross Practice



Practice

Tall Height is dominant = T
Short Height is recessive = t
Purple Flowers are dominant = F
White Flowers are recessive = f
Straight Hair is dominant = H
Curly Hair is recessive = h

MONOHYBRID CROSS

Ex1: Tt x TT



Ex2: FF x ff



Ex3: Heterozygous parent for purple flowers is crossed with homozygous recessive for white flowers.



Ex4: Two heterzygous parent for tall height is crossed.

DIHYBRID CROSS

Ex5: TTHh x Tthh








Ex6: A tall and purple homozygous dominant plant is crossed with a heterozygous plant.








PEDIGREE ANALYSIS

Case of the Tell Tale Gene