Mendelian GeneticsBio 40S - Kelvin

Traits and Heredity

Every living organism is

made up of many different

traits, or distinguishing

characteristics, that make it

unique (ex: eye colour)

Transmission of traits from

one generation to the next

is called heredity.

GENETICS:

study of heredity

HEREDITY:

the passing of traits from parents to offspring

Gregor Mendel

Gregor Mendel

Spent 8 years studying

how traits were inherited

(1856 – 1863)

The first to identify

discrete units of heredity

(genes)

Selectively fertilized pea

plants with the pollen

from other plants and

analyzed the hereditary

patterns of certain traits.

Gregor Mendel

The first person to predict how traits were transferred between generations.

Concluded that inherited characteristics were carried in discrete, independent

units (later called genes)

Segment of DNA

Genetic Unit of instruction the code for a trait

Gene

Blending Theory of Inheritance

Before Mendel’s experiments, it had been

thought that a child was just a “blend” of

their two parents since Ancient Greece.

This failed to account for scenarios like two

brown haired parents having a blonde child.

By accounting for genes, Mendel rejected

this old theory.

Pea Plants

1. peas grow and reproduce quickly

2. their mating can be controlled

3. Pea plants can be self-fertilized or cross-fertilized

4. They have easily observable traits

Segregation and Independent Assortment

Mendel developed two extremely important genetic laws.

Law of Segregation:

The factors of inheritance (genes) are normally paired BUT are

separated or segregated in the formation of gametes.

The gene from each parent splits up, 50/50 chance of either

Law of Independent Assortment:

Each factor’s distribution in the gametes is not related to the

distribution of any other factor.

Genes for hair colour and eye colour arrange separately.

Many combinations

Traits

Each trait has only 2 possible forms or variations.

Yellow or green, smooth or wrinkled, tall or

short, purple flower or white flower, etc.

There are 2 different forms (alleles), dominant

and recessive, and every individual has 2 of

these genes (one from each parent)

Allele: A version of a gene

(can be dominant or recessive)

Alleles

A Purebreeding organism has either 2 dominant or 2

recessive alleles

When a Purebred Dominant individual and a Purebred

Recessive individual have offspring, the offspring will

be a hybrid and will get one allele from each parent

The Dominant allele “masks” the recessive allele

resulting in a dominant phenotype

Homozygous: Two of the same alleles

(both dominant or both recessive)

Heterozygous: One of each type of alleles

(one dominant, one recessive)

Capital letter represents dominant

Lowercase of same letter is recessive

If purple flower dominant to white…

•“Pp” represents allele for purple

•“Pp” represents allele for white

We will work to use letters that do not look the same both ways after this example ☺

Notation