1. Sci9ence of Heredity Lessons 1 & 2
Chapter 4
Sci9ence of Heredity
Lessons 1 & 2

2. Lessons 1&2- Genetics Heredity Alleles Genetics- study of heredity.
Passing of traits from parent to offspring
Alleles
Different forms of a trait that a gene may have
Ex. Having dimples or not having dimples?
Genetics- study of heredity.
The study of how
traits are inherited
through the
interactions of alleles

3. What are Phenotypes and Genotypes?
Phenotype: PHYSICAL appearance, or visible traits
Genotype: Organism’s GENETIC makeup, or alleles.
Homozygous: Two Identical alleles for a trait.
Heterozygous: Two Different alleles for a trait.

4. Mendel- The Father of Genetics
Australian Monk
Conducted genetic experiments using the garden pea.
1st person to trace one trait through several generations.

5. Mendel crossed 2 plants with different expressions of the trait and found that the new plants all looked like one of the two parents.
Hybrids
They received different genetic information (alleles) for a trait from each parent.
Dominant
Factors that dominate, or covered up.
In peas – Tall Dominated over Short Ex. Tt (heterozygous for tallness)
Recessive
Factors that seem to disappear
In peas- the short formed disappeared

6. Which Alleles are dominant?
Which alleles are recessive?

7. Punnett Square Shows you all the ways in which alleles can combined.
Handy tool used to predict results.
A lower case letter = recessive allele.
An upper case letter = dominant allele.

8. The letters form a code!!! Genotype Phenotype
Genetic makeup, of an organism
Ex. BB
Phenotype
The way an organism looks and behaves
Physical appearance of an organism
Ex. Brown hair

9. Most cells in your body have two alleles for every trait. Homozygous
Located on chromosomes.
Homozygous
An organism with two alleles that are the same
Ex. Homozygous dominant (TT) or
Homozygous recessive (tt)
Heterozygous
An organism that has two different alleles for a trait.
Ex. (Tt) or (Rr)

10. Let’s Make a Punnett Square
Punnet Square- a genetic tool that uses letters to represent dominant and recessive alleles.
letters representing two alleles from one parent are written along the top.
* Letters representing two alleles from the other parent are placed down the side.
Each square of the grid is filled in with one allele donated by each parent.
Letters= possible genotypes
Probability- helps determine the chance that something will occur.

12. F f F f 1 2 3 4 Male: top (Ff) (F) dominant for freckles
Female: side (Ff) (f) not having freckles
F f 1 2 3 4 F f

13. F f FF Ff F f 1 2 3 4 ff Male: top (Ff) (F) dominant for freckles
Female: side (Ff) (f) not having freckles
F f 1 FF 2 Ff 3 4 ff F f

14. Child in Box 1 = homozygous for freckles
Phenotypic Ratio: 3:1
Which box represents a child who does not have freckles: Box 4- ff
Box 3 represents: Ff- heterozygous for freckles

15. Using Pedigrees Pedigree
Tool for tracing a trait through generations of a family.
Important for breeding animals or plants
When geneticists understand how a trait is inherited, they can predict the probability that a baby will be born with a specific trait.