Genetics

Vocabulary Genetics: The study of heredity, Genetics: The study of heredity, Heredity: the passing on of traits from an organism to its offspring Heredity: the passing on of traits from an organism to its offspring

Gregor Mendel An Austrian monk and biologist An Austrian monk and biologist Worked during the 1860s Worked during the 1860s Experimented with pea plants Experimented with pea plants Called “The Father of Genetics” for his discoveries which began the field of genetics Called “The Father of Genetics” for his discoveries which began the field of genetics Public Domain Public Domain

Mendel did his experiments in the monastery gardens. Public Domain

Why did Mendel choose to work with peas? Peas grow and reproduce quickly so he could study many generations. Peas grow and reproduce quickly so he could study many generations. They had a variety of different traits he could study at the same time. They had a variety of different traits he could study at the same time. He could easily breed or cross them through pollination. Peas normally self- pollinate but can be artificially cross- pollinated by transferring pollen from one plant to another mechanically. He could easily breed or cross them through pollination. Peas normally self- pollinate but can be artificially cross- pollinated by transferring pollen from one plant to another mechanically.

Experiment 1 Short pea plants X short pea plants All short pea plants Short plants are true breeders – short plants always have short plants as offspring

Experiment 2 Tall pea plants X Tall pea plants Sometimes Sometimes Sometimes Sometimes All tall pea plantsMostly tall plants (true breeders)with some short plants All tall pea plantsMostly tall plants (true breeders)with some short plants

Experiment 3 P 1 (Parent Generation): True breeding short X True breeding Tall Short X Tall P 1 Tall F 1 75% Tall & 25% Short F 2 Mendel concluded each plant must contain two factors for a particular trait – he called them characters, we call them genes.

Dominant vs. Recessive Genes are the units of heredity. Genes are the units of heredity. A gene may have different forms that are expressed as different traits A gene may have different forms that are expressed as different traits They may be dominant (the stronger trait) or recessive (the weaker trait) They may be dominant (the stronger trait) or recessive (the weaker trait) If both are present in an organism the dominant trait will be expressed and the recessive trait hidden. If both are present in an organism the dominant trait will be expressed and the recessive trait hidden. The different forms are called alleles. The different forms are called alleles.

Seven Traits of Peas that Mendel Studied 1. Plant Height - tall or short 2. Seed Shape – round or wrinkled 3. Seed Color – yellow or green 4. Pod Color – yellow or green 5. Position of Flowers – axial or terminal 6. Pod Shape – inflated or pinched 7. Flower Color – violet-red or white

Dominant vs. Recessive Dominant traits are represented by capital letters and corresponding recessive traits as the same letter in lowercase Dominant traits are represented by capital letters and corresponding recessive traits as the same letter in lowercase For example: the dominant tall allele is T and the recessive short allele is t For example: the dominant tall allele is T and the recessive short allele is t

Mendel’s Experiment 3 Using Symbols for Alleles P 1 TT X tt Purebred F 1 Tt Tt X Tt Hybrid Tt X Tt Hybrid F 2 TT Tt Tt tt F 2 TT Tt Tt tt 25% 50% 25% 25% 50% 25%

By convention, the dominant gene is written first in a gene pair no matter which parent it comes from By convention, the dominant gene is written first in a gene pair no matter which parent it comes from If an organism has two alike alleles (both dominant or both recessive) it is purebred for that trait If an organism has two alike alleles (both dominant or both recessive) it is purebred for that trait If an organism has one dominant allele and one recessive allele it is hybrid for that trait If an organism has one dominant allele and one recessive allele it is hybrid for that trait

The Law of Segregation A law that states that gene pairs separate during sex cell formation A law that states that gene pairs separate during sex cell formation This means that each sex cell (egg or sperm) contains only one allele for each gene This means that each sex cell (egg or sperm) contains only one allele for each gene

The Law of Independent Assortment A law that states that each gene pair for a trait is inherited independently of the gene pairs for all other traits A law that states that each gene pair for a trait is inherited independently of the gene pairs for all other traits Therefore if you have two hybrid traits, Tt and Rr, the sex cells may have the following combinations of alleles TR, Tr, tR or tr Therefore if you have two hybrid traits, Tt and Rr, the sex cells may have the following combinations of alleles TR, Tr, tR or tr

Incomplete Dominance Discovered by German botanist Karl Correns Discovered by German botanist Karl Correns When neither allele in a gene pair masks the other entirely but their effects blend to produce a result different from the purebred of either allele When neither allele in a gene pair masks the other entirely but their effects blend to produce a result different from the purebred of either allele

Incomplete Dominance First example: Red Four O'clocks X White Four O’clocks Red Four O'clocks X White Four O’clocks (RR)(WW) Pink Four O’clocks (RW) Public Domain:

Incomplete Dominance Second example: Creamy-white Horse X Chestnut-brown Horse (WW)(BB) Creamy-white Horse X Chestnut-brown Horse (WW)(BB) Palomino Horse (BW) A palomino is pale golden-brown with a white mane and tail Public Domain:

The Principals of Genetics 1. Traits, or characteristics, are passed on from one generation of organisms to the next generation. 2. The traits of an organism are controlled by genes. 3. Organisms inherit genes in pairs, one gene from each parent

The Principals of Genetics 4. Some genes are dominant, whereas other genes are recessive 5. Dominant genes hide recessive genes when both are inherited by an organism. 6. Some genes are neither dominant nor recessive. These genes show incomplete dominance.