Genetics: How genes make us who we are

• Genetics is the study of heredity• Heredity is the passing of traits from one

generation to the next• YOUR biological inheritance is the unique

blend of genes that are passed to you by your parents

II. Mendel- The Father of Genetics

• Gregor Mendel– Lived 150 years ago– Austrian monk– Good at Math– Taught high school– Grew pea plants – Careful and persistant

Mendel’s Model Organism – the Garden Pea

Mendel noticed that the peaPlants in his garden differed.He noticed 7 differences or traits which he decided to study.

Genetics Vocabulary to Know

• Trait – Inherited feature or characteristic: examples are eye

color, pea plant height• Allele

– One form of a trait. Example eye color: blue eyes or brown eyes

• Genotype– What the genes say Hh or HH or hh

• Phenotype– Outward appearance: having blue eyes

Mendel asked how are these traits inherited

IV. Mendel’s 1st Experiment• He mated tall x short plants and got all tall• What happened to the short plants, why did’nt the

two parents traits BLEND in the offspring??????

PP

FF11

V. Mendel’s 2nd Experiment• QUESTION: What happened to the short plants???• 2nd EXPERIMENT: Mendel allowed both the tall plants and the

short plants to self-pollinate• RESULTS: NOW the short plants ‘come back’, they can be seen

in the next generation BUT only ¼ plants are short

FF11

FF22

Characters investigated by Mendel

Mendel repeated this experimentWith 7 more pea plant traits

The results were always thesame

No matter which trait Mendellooked at he saw the 3:1 ratio in the off spring

He drew 3 conclusions from theseexperiments. Today we under-stand the molecular basis of Mendel’s findings.

Monohybrid Crosses Yielded Consistent Results

Therefore, the Principle of Segregation indeed is a general principle of genetics.

Mendel’s CONCLUSIONS from his experiments

Traits are inherited by some factor (which we now call genes) being passed from parent to offspring

There are different forms of each factor (gene) that produce the traits, these are alleles. Some alleles are dominant and some are recessive, the recessive will only show if the dominant is not present.

Each parent organism must not be giving BOTH of it’s alleles, they are separating and passing on only ONE to the offspring

Here is Mendel’s first experiment again with seed color instead of tall vs short

Imagine we can look inside the plant at the genes, the genotype, as well as see the outside, the phenotype

The genes for yellow color are YYThe genes for green color are yyYellow(Y) is dominant to green(y)

A Punnet square is used to show the possible results of the mating or cross

P generation is the parents

F1 is the first generation of children

Staying the Course – Mendel Continued Crosses to the F2 (the grandchildren)

What was learned?

The green trait was not lost or altered, even though it disappeared in the F1.

One trait is dominant to the other in its expression.

The reappearance of the recessive trait in ¼ of the F2, suggests genes come in pairs that separate in the formation of sex cells.

NOW 150 years later!!! we know more about Genes, Alleles, and Chromosomes:So this is what is happening inside the chromosome…

VI. More terms

Homozygous – a parent that has two identical alleles for a gene (ex: TT, tt, AA, aa)

Heterozygous – a parent that has two different alleles for a gene (ex: Tt, Aa)

Recessive – form of a trait which does not appear if in the presence of the other form, blue eyes

Dominant – form of the trait which is seen even if both alleles are present, example brown eyes