Ch. 11. A Brief History In the past, people did not understand how traits were inherited, but there were many guesses based on things that could be observed.

Ch. 11

A Brief History

In the past, people did not understand how traits were inherited, but there were many guesses based on things that could be observed.

Two theories emerged….

Blending Theory - offspring are a straight mix

Particulate Theory

traits are inherited as "particles", offspring receive a "piece" from each parent, some pieces may hide the others Golden Doodle

The study of heredity (how traits are passed from one generation to the next)

Gregor Mendel was the first person to discover how traits are passed from one generation to the next (even

though no one knew what DNA or genes were yet).

He did this by experimenting with pea plants.

Mendel did his study on pea plants

which have many traits

-tall/short

-purple /white flowers

-round/wrinkled seed

• True-Breeding Plants -always

create plants that look like

themselves

• Hybrids – offspring of true-

breeding plants

Tall x Short = Hybrid

•Some traits are dominant over others.

•Tall x Short = all tall offspring (hybrids)

*Tall is the dominant trait

* Short is recessive

Molecule that contains the instructions for making all of the proteins needed for life

DNA wraps around proteins called histones. This forms chromatin.

When the chromatin condenses it forms chromosomes.

For every chromosome, we inherit two copies. One from mom and one from dad

Since they are the same type of chromosomes, they are called

homologous.

Genes are passed from parents to their offspring

The adult has two copies of each gene -- one from each parent.

These genes segregated from each other when gametes are formed-The alleles for different genes usually segregate independently of one another.

Forms of a gene may be dominant while others are recessive

Each “recipe” on the DNA is called a gene. Ex. Hair color and hair texture are

two different genes found at different loci (locations) on the

chromosomes.

There is often more than one version for a gene.

These are called alleles.

Example:▪ Gene = flower color

Alleles = purple or white

A dominant allele will ALWAYS be expressed if it is present in the DNA.

A recessive allele will be hidden or “masked” if a dominant allele is present. The only way an individual can

express a recessive trait is by inheriting two recessive alleles.

The genotype tells you which alleles an individual has inherited. Capital letters are used for dominant traits.

Lowercase letters are used for recessive traits.

The rule is to choose the first letter of the dominant trait. Example: Brown eyes are dominant over green eyes, so you would use “B” for brown eyes and “b” for green eyes.

An individual with two different alleles (usually one dominant and one recessive allele).

Genotype =

An individual with two of the same alleles is called homozygous.

Can be homozygous recessive

or homozygous dominant.

The phenotype tells you which trait is physically expressed in the individual.

Example: These puppies’ phenotype is yellow fur.

When a parent makes sperm or eggs, their

genes separate

        (PRINCIPLE OF SEGREGATION)

The GAMETES (egg or sperm) contain either

a T allele (tall) or a t allele (short)