Genetics: The science of Heredity.

Where to begin? Gregor Mendel

§The "father of modern genetics” §Born on July 22, 1822 in Heizendorf, Austria. §Mendel raised and tested over 28,000 pea plants between the years 1856 and 1863, carefully analyzing seven pairs of seed and plant characteristics.

Gregor Mendel §He specifically studied plant height, pod shape, pod color, flower position, seed color, seed shape and flower color. §He made two very important generalizations from his pea experiments, know today as the Laws of Heredity.

Gregor Mendel §Law of Segregation Mendel's First Law §Law of Independent Assortment Mendel's Second Law

A few terms…... §Traits l Physical characteristics §Heredity l The passing of traits from parents to offspring. §Genetics l The study of heredity §Purebred l Always produces offspring with the same traits as the parents.

Back to Mendel §His first experiment……using pea plants he crossed purebred tall plants with purebred short plants plants. §What do you think he got? CD

Back to Mendel §Turns out, the first generation of plants were all tall! No short ones!

More of Mendel §He then took two of the offspring plants and crossed them…….What do you think he got? CD

More of Mendel §Holy Smokes…He got 75% Tall plants and 25% short plants!..How could this be? CD

Mendel Explained….. §From this experiment and others, Mendel concluded that factors must control the inheritance of traits. §These factors must exist as pairs..one from the male parent and one from the female parent.

Mendel Explained….. §Today, we call these genes l factors that control traits. §The different forms of a gene are called alleles.

Mendel Explained….. §Individual alleles control the inheritance of a trait. §Some alleles are dominant while others are recessive. §A Dominant allele trait always shows if the organism has the allele §A recessive allele is masked if a dominant allele is present.

How can we look at this... §Scientist use a simple grid to help sort out genetics and inheritance called a Punnett Square.

Punnett Squares §Chart that shows all possible combinations of alleles that can result from a genetic cross.

Punnett Squares Parent Generation P

Punnett Squares Parent Generation P Offspring Generation F1

Punnett Squares Offspring Generation F1

Punnett Squares Offspring Generation F1 Offspring Generation F2

Punnett Squares If an offspring has two different alleles for a trait, it is called a hybrid. Hybrid: Two different alleles for a trait.

Punnett Squares Let’s predict another... Offspring Generation F2

Couple more terms…. §Now that we have a basic concept of how gene pairs mix to express traits, we should give this mixing and expressing some niffy science terms…. §Phenotype: An organisms physical traits. l Height, color, shape, ear attachment etc. §Genotype: An organisms genetic makeup or allele combination.

Still More…... §A touch more detail……. §If an organisms genotype has two identical alleles it is called homozygous §Homozygous: Two identical alleles.

Which ones are Homozygous?

Still More…... §If an organisms genotype has two different alleles it is called heterozygous §Heterozygous: Two different alleles. l The same thing Mendel called a hybrid. l Hybrid is still commonly used.

Which ones are Heterozygous?

What about us? §Does this all work the same for humans? §Sure it does! §Let’s start with the simplest to sort…Male and Female

Human Genetics Female sex cell…Egg Male sex cell…sperm

How about sex-linked genes §Color blindness is carried only on the X chromosome. Usually expressed as X C or X c. What if you have a color blindness carrier(not color blind) for a mom and a normal father?

Sex-linked genes