DO NOW • Observe the colors

of each puppy in the photo. Record each puppies’ coat colors and patterns. Include as many details as you can.

• Observe the mother dog in the photo. Record her coat color and pattern.• Think it over: Based on your observations, describe what you think the puppies’ father might look like. Identify the evidence on which you based your inference.

GENETICS – THE SCIENCE OF HEREDITY

“Father of Genetics”

• Mid 1800’s, a priest who worked in the gardens of his monastery.

• Mendel was curious why some of the plants had different physical characteristics or traits.

• He noticed that often plants were similar to the previous generation, or their parents.

• He also noticed some plants were very different from their parents.

• He hypothesized as to how those traits were passed on.

Mendel’s work formed the foundation of today’s genetics…

• Heredity – the passing of traits from parents to offspring

• Genetics – scientific study of heredity

Why Peas?

• Lots of traits that exist in only two forms– Ex. tall/short (no medium), green/yellow

• Produce large numbers in each generation– Easy to collect lots of data

• Even though they usually self-pollinate, they could be cross pollinated – Mendel took pollen from the stamen of one

plant and placed it on the pistil of another

Mendel’s Experiments• Mendel started with

purebreds– Plants that always produce

offspring with the same form of trait

– How do you get a purebred?

• First experiment: the Parental Generation

(P generation)– Tall x Short

Mendel’s Experiment• All of the offspring of this cross are called the F1

generation.– F stands for filial which means “son” in Latin

•The F1 generation was ALL TALL!

–Even though one of the parents was short, all the plants were tall; the shortness trait seemed to disappear!

Mendel’s Experiments• Mendel then crossed two of the F1

plants

• The results in the F2 generation were very different

• The shortness trait came back!• Out of all the plants that grew, about ¾

were tall, while about ¼ were short.

Mendel’s Experiments

• Mendel wanted to see if this happened with other traits, so he cross-pollinated the pea plants and tested six other traits

• He always got the same results.

Flower Color

P generation - Purple purebred x White purebred

F1 generation - All Purple

F1 x F1 - Purple x Purple

F2 generation – ¾ Purple and ¼ White

Why did some traits show up more than others?

• Mendel reasoned that there must be some individual factors that control what gets passed on from parent to offspring– The female parent contributes one “factor”

while the male contributes one “factor”

• He also reasoned that one factor can mask or hide another factor.– Tall hides short; Purple hides white

• Genes: factors that control traits– Sections of DNA that

give instruction for one certain trait.

• Alleles: different forms of a gene– Gene: Plant Height– Allele: Tall or Short– Gene: Tongue Rolling– Allele: Can or Can’t

What is the Difference?

Individual alleles control the inheritance of traits

• Some alleles are DOMINANT– The trait always shows up

when its present

• Some alleles are RECESSIVE– Trait gets masked or

hidden• Will only show up if the

dominant trait is not present

Black fur is dominant to white fur in rabbits

DOMINANT AND RECESSIVE TRAITS

Use the Diagram on page 113 to determine which plant alleles were dominant and which were recessive:

• Plant height – Tall is dominant to Short• Pea Pod – Green is dominant to Yellow• Seed shape?• Seed Coat Color?• Flower Color?

Understanding Mendel’s Crosses

• Mendel started with purebreds: two identical alleles for stem height

tall/tall short/short

tall/short• The F1 generation were hybrids:

two different alleles for the one trait.

Understanding Mendel’s Crosses

• He next crossed two of the hybrids:tall/short x tall/short

Four possible resultstall/tall = tall planttall/short = tall plantshort/tall = tall plantshort/short = short plant

Using Symbols in Genetics• To make it easier, geneticists use

symbols to represent the alleles.– Capital letters represent the dominant trait– Lowercase letters represent the recessive

trait.

• Purebred tall = TT• Hybrid tall = Tt• Purebred short = tt

Describe Mendel’s crosses AGAIN, but his time use the letter symbols to represent the alleles for the gene PLANT HEIGHT.

Practice using the symbols

• Gene: Ability to roll tongue• Alleles: Can/can’t• Can is dominant to can’t• Use “R” to represent the trait• Purebred can = • Hybrid = What does it look like?• Purebred can’t =

Practice using the Symbols

• Gene: Eyecolor• Alleles: Brown/blue• Brown is dominant to blue• Use “B” to represent the trait• Purebred brown = • Hybrid = What color?• Purebred blue =