Introduction to Genetics

• Why you are you and not anybody else!

• However, children born from the division of one fertilized egg ARE genetically identical!

Are you Unique?

• Dimples?

• Able to roll your tongue or not?

• Curly or straight hair?

Are You Unique?• Widow’s

Peak or not?

• Free or attached lobes?

Are You Unique?• Second toe

longest or not?

Are YOU Unique?

• Complete table of your own traits (Anyone with a tail and blue skin?)

• Complete table of the class traits

Traits• Individuals have

many characteristics or traits that make each of us unique.

• Trait = specific characteristic that varies from one individual to another

Genetics – The Study of Heredity

• Interest in the passing of traits from one generation to the next is not new

• Agriculture was developed around 12,000 years ago. People selected the plants and animals with the best traits to raise.

• Example: Farmers selected wild grass plants with the largest seeds to produce corn

Gregor Mendel – Father of Genetics

• Born in 1822 in what is today the Czech Republic.

• At university he studied for the priesthood, as well as, math and science.

Gregor Mendel – Father of Genetics

• As an adult he lived in a monastery. He taught high school and worked in the monastery garden.

• Between 1856-1868, Mendel conducted experiments on inheritance with the common garden pea.

Pea Plants

Mendel’s Genetic Work

• Mendel experimented with 7 different traits of peas.

Mendel’s Genetic Work

• Mendel was extremely lucky in his choice of the garden pea for his study.

• This was a perfect organism for the study of inheritance.

What made the Pea so Perfect?

• Several of the characteristics were controlled by individual genes. – height of plant– color of pea pod

What made the Pea so Perfect?

• Reproduce sexually• Large number of

offspring (peas on a pod)

• Easy to handle in a lab

What made the Pea so Perfect?

• Genetic crosses are easily controlled

• Peas are True Breeding plants (=the parent plant normally produces offspring identical to itself), because they self-pollinate.

Mendel’s Genetic Research

• Mendel published his findings in the 1860’s but his ideas were ignored.

• At the time of Mendel’s publication of his work, scientists believed ALL inheritance worked through “blending.”

What happened to Copernicus and Galileo when they had new

ideas ?

Blending

• Example: White animals live in a meadow

• An animal is born with a mutation making it red

Blending

• Red animal breeds with white animals results in some pink animals

• Pink animals breed with white animalsresults in light pink animals

Blending• Light pink animals breed with white animals

results in white animals.

• Mendel’s work with garden peas proved that blending did NOT explain the transfer of traits from one generation to the next.

Mendelian Genetics

• Mendel studied 7 traits• He studied one trait at a time• He began his work by breeding together two

True Breeding plants.• A True Breeding plant self-pollinates and

always has offspring that share its traits. • Example: Tall plants always produce tall

plants. Short plants always produce short plants.

Mendel’s Experiments

• Mendel asked, “What happens if I cross a true breeding tall plant with a true breeding short plant?”

 

• _________________________________

According the theory of blending, what will be the results of this cross?

Medium tall plants

Mendel’s Results

• What were the ACTUAL results of a cross between a true breeding tall and a true breeding short plant?

• All of the offspring were TALL.

Definitions• True breeding plants are the

– Parents or P generation• The offspring of the P generation are the

– First Filial (filial = son in Latin) or F1 generation

How did Mendel conduct his Experiment?

• Flower Worksheet

♂= male

♀=female

Pea Flower

Mendel’s Experiment

• Mendel removed the stamen (♂) from a SHORT plant.

• He then removed pollen from the anther of a tall plant and brushed it on the stigma (♀) of a SHORT plant.

Mendel’s Results

• The plants produced seeds.• The seeds were planted • Every seed produced a TALL plant

• Mendel’s First Conclusion: biological inheritance is determined by factors that are passed form one generation to the next.

• Today we know these factors as genes. P generation

F1 generation

Mendel’s Second Experiment

• Mendel crossed plants from the F1 generation together.

• He created thousands of crosses this way.

• Each flower produced seeds.

• Thousands of these seeds were planted and grew into the F2 generation.

Mendel’s Results of the F1 Cross

• Mendel observed the thousands of plants he grew from seeds.

• He found the missing trait had reappeared!!

• Among the new F2 generation there was a 3:1 ratio of Tall to Short Plants

P generation

F1

generation

F2

Generation

Mendel’s Second Conclusion

• Second Conclusion: Principle of dominance – Some alleles are dominant and some are recessive. An organism with one or two dominant alleles for a particular form of a trait will always have that form.

**********************• An organism inherits TWO alleles for

every trait. One from its mother and one from its father.

Vocabulary

• Gene –

• Allele –

• Dominant -

• Recessive -

• Hybrid =

• Pure =

• True breeding =

Vocabulary

• Gene - unit of heredity information• Allele – form of a gene (Tall/Short). • Dominant - stronger of two alleles• Recessive - weaker of two alleles• Hybrid = offspring of parents with different

traits. A hybrid has one recessive gene and one dominant gene

• Pure = both genes are the same (2 recessive or 2 dominant) = homozygous

• True breeding = P generation = pure

Rules for Genetic Problems

• Two alleles for a gene are represented with the same letter.

• Dominant alleles are represented with an uppercase letter, and recessive alleles are represented with a lower case letter.

• The letter representing the gene is usually the first letter of the dominant trait.

• For example: Tall allele = T; Short allele = t

Rules for Genetic Problems

• Try this:– A pea plant has two alleles for seed color. – Yellow is the dominant seed color – Green is the recessive seed color. – What is the symbol for yellow seed color?

_____________– What is the symbol for green seed color?

_____________

Y

y

Rules for Genetic Problems

• Since a plant inherits two alleles for seed color it may be– YY = yellow seeded plant– Yy = yellow seeded plant – yy = green seeded plant. 

More Vocabulary

• Homozygous genes = same alleles for the trait (YY, yy) = pure

• Heterozygous genes = different alleles for the trait (Yy) = hybrid

• Genotype = genetic make-up of an organism.

• Phenotype = physical characteristic of an organism.

Punnett Squares

• Named after R.C. Punnett, British geneticist, 1875-1967

• Used to understand the probability of the outcome of a genetic cross.

Punnett Square F1 generation cross

Worksheets

• Genetic Crosses