Genetics: The Study of HeredityI. Review

A. Why do you look like your parents? They gave you your DNA

B. How is this information transferred? Through sexual reproduction

(gametes and fertilization)C. What do we call a segment of DNA that

codes for a protein?Gene

D. Where are genes located?On chromosomes

E. How many chromosomes do humans have? 46 (23 from Mom, 23 from Dad)

F. How many genes are on human chromosomes?

Estimated at about 20,000 - 25,000 genes in the human genome, containing 3 million base pairs

II. General InfoA. Genetics is the study of heredity

1. Heredity – passing of traits from parent to offspring (baby)

2. Another word for “trait” is characteristic. A trait is something that can be scientifically observed, such as:

What determines our What determines our traitstraits??Our Our genesgenes!!

Another genetic trait we can investigate is called hitchhikers thumb:

B. Gene - a segment of DNA that codes for a protein. It controls an organism’s form and function.

1. Each gene can control one or more trait (ex. human eye color is controlled by at least 5 different genes!)

2. Human DNA is made of ~ 20,000 - 25,000 genes

3. A gene can have different forms or physical expressions of a trait known as an allele (ex. You have a gene for little finger type with two alleles: bent and straight)

C. Organisms get half of their genes from each parent when sperm and egg meet

Our genes influence how

we look

And in many cases genes

influence how we act

III.III. Gregor Mendel: Gregor Mendel: ““Father of Modern Father of Modern GeneticsGenetics”” (1824-1884) (1824-1884)

A.A. MendelMendel’’s Lifes Life

1.1. Austrian monk born in current Czech Austrian monk born in current Czech RepublicRepublic

2.2. Joined a monastery, then studied math Joined a monastery, then studied math and science at the U. of Viennaand science at the U. of Vienna

3.3. As a monk he taught high school and As a monk he taught high school and cared for the monastery garden, which cared for the monastery garden, which is where he developed his ideas on is where he developed his ideas on geneticsgenetics

4.4. Significance of his work was not Significance of his work was not recognized until the early 1900recognized until the early 1900’’ss

B. Mendel’s Experiment1. He cross-bred pea plants with different

characteristics, then studied 7 plant traits (seed/pea shape, color, height, etc.) of the hybrid offspring

Seed Shape

Flower Position

Seed CoatColor

Seed Color

Pod Color

Plant Height

PodShape

Round

Wrinkled

Round

Yellow

Green

Gray

White

Smooth

Constricted

Green

Yellow

Axial

Terminal

Tall

Short

Yellow Gray Smooth Green Axial Tall

2. All of the first generation offspring (F1) had the characteristics of only one of the parent plants (P)

DRAW THIS Why did the “short” trait appear in the F2

generation but not in the F1 generation?

P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Although Mendel did most of his

genetics work on pea plants, his ideas about

genetics also apply to

humans…

IV. Mendel’s Basic Principles of GeneticsA. Every trait is determined by a pair of

“units”B. Each parent provides one unit (allele)C. Each gene has forms called an allele.

A. If an organism has 2 of the same alleles for a trait, it is purebred.

B. If the organism has different alleles for a trait, it is hybrid

C. Example in pea plants: Height1. T = tall allele t = short allele2. Purebred plant is TT or tt3. Hybrid plant is Tt

D. Some alleles can cover-up the expression of the other

a. Dominant allele always showb. Recessive allele is hidden when

it is with a dominant allele

E. In the formation of sperm and eggs (gametes), one member of each allele separates into different gametes. This is called segregation

F. How the alleles segregate during gamete formation is determined by chance. This is called Independent Assortment

V. Important TermsA. Genotypes are the letters used to

describe the two alleles of a gene (ex. TT, Tt, tt)

1. Homozygous genotype means both alleles are the same (purebred) therefore we use the same letters

a. Dominant alleles are represented by Capital letters (ex. a plant that has two dominant alleles is homozygous dominant = TT)

b. Recessive alleles are represented by the same letter but lower case (ex. a plant that has two recessive alleles is homozygous recessive = tt)

A. Heterozygous genotype (hybrid) means one dominant and one recessive allele(ex. heterozygous = Tt)

B. Phenotype1. The physical expression of the

genotype (Ex. Eye, hair, skin color. Flower color, shape and location)

VI. Probability and Punnett Squares

A. Genetics & Probability1. Probability is the likelihood that a

particular event will occur (e.g. coin toss)

2. Can be used to predict the outcomes of genetic crosses

3. Probability does not predict precise outcomes

4. The larger the number of events, the more accurate the probability

5. In genetics, the larger the number of offspring, the closer the resulting offspring will be to what was predicted

B. Punnett squares1. Punnett square is a diagram used to

determine the gene combinations that might result from a cross

2. Used to predict genetic variations that will result from a cross

Monohybrid CrossMonohybrid Cross(cross for only one trait)(cross for only one trait)

Draw