Introduction to Genetics

Heredity the passing of traits from parents to offspring

Genetics the branch of biology that studies heredity

Gene piece of DNA that codes for a protein that is responsible for a trait found on chromosomes

Genes

Gene piece of DNA that codes for a protein that is responsible for a trait found on chromosomes basic unit of heredity

Trait features of an organism i.e. color of a flower

Allele different versions of a gene i.e. purple or white flowers on a pea plant

Dominant trait that is expressed even when another form of the trait is present allele that shows itself in the presence of the other usually represented with a capital letter i.e. purple flowers in pea plants (P)

Recessive trait that is not expressed when the dominant form of the trait is present allele that is hidden in the presence of the other usually represented with a lower case letter i.e. white flowers in pea plants (p)

Dominant vs. Recessive

Homozygous both alleles for a trait are the same can be homozygous dominant (PP, purple flowers) or homozygous recessive (pp, white flowers)

Heterozygous the alleles for a trait are different a plant with one copy of the dominant gene (P, for purple flowers) and one copy of the recessive gene (p, for white flowers) would produce purple flowers (Pp)

Homozygous vs. Heterozygous

Genotype the combination of alleles an organism has for a trait genotype = genes Ex: PP, Pp, or pp

Phenotype the physical appearance of a trait phenotype = physical Ex: purple or white

Monohybrid cross breeding that involves one pair of contrasting traits i.e. breeding a purple-flowered plant with a white-flowered plant

True-breeding breeding of organisms that will only produce offspring that have the same trait i.e. a purple flower that will only produce purple-flowered offspring when bread with a similar purple flower

P generation parental generation generally are true-breeding in controlled experiments the first two individuals that mate in a genetic cross

F1 generation first filial generation filialis – Latin, meaning “a son or daughter” the offspring of a cross of two parents (P) in a genetic cross

F2 generation second filial generation the offspring of a cross between two F1 individuals in a genetic cross “grandkids” of the P generation from “inbreeding” the F1 generation

Thomas Andrew (T.A.) Knight (a little background information…) A British horticulturist and botanist (plant scientist) Lived 1759-1838 Most of his influential work was discovered after his death

Thomas Andrew (T.A.) Knight bred a variety of true-breeding garden peas with purple flowers with a different variety of true-breeding garden peas white flowers (P generation) all offspring (F1 generation) had purple flowers when offspring were bred together, the next generation (F2 generation) had some purple flowers and some white flowers

Gregor Mendel

Gregor Mendel (a little background information…) An Austrian monk Lived 1822-1884 Trained as a mathematician and natural scientist. First to present the principles of heredity. Result of studying the inherited traits of peas over a period of eight years. His work was published but overlooked by the scientists of his time (1865).

Gregor Mendel (a little background information…) His work was rediscovered in 1900 after chromosomes had been named and their movements recorded in meiosis. Observed that there was a perfect match between the observed behavior of chromosomes in meiosis and Mendel’s hypothesis of inheritance.

Gregor Mendel “father of modern genetics” Mendel conducted work very similar to Knight’s work Mendel counted the number of each kind of offspring in each generation the data was then analyzed and used to make predictions about future generations

The Work of Gregor Mendel (a little background information…) Holt Biology, pg. 163

The Work of Gregor Mendel (a little background information…) Holt Biology, pg. 164

The Work of Gregor Mendel (a little background information…) Holt Biology, pg. 163

Gregor Mendel From his data analysis, Mendel created two Laws that helped him make predictions about future generations Law of Segregation Law of Independent Assortment

Law of Segregation two alleles for a trait separate when gametes are formed occurs because homologous chromosomes separate during Meiosis I

Law of Segregation & Meiosis

Law of Segregation

Law of Independent Assortment the alleles of different genes separate independently of one another during gamete formation

Law of Independent Assortment

Law of Independent Assortment the alleles of different genes separate independently of one another during gamete formation occurs because different pairs of homologous chromosomes separate RANDOMLY during Meiosis I

Law of Independent Assortment Holt Biology, pg. 163

The Work of Gregor Mendel (a little background information…) Holt Biology, pg. 164

Theory Building Mendel’s Laws pre-dated our modern understanding of meiosis When new technologies were created to allow us to observe the steps of meiosis, they helped to confirm what had been predicted in theory

Summary Why was Mendel’s work “more scientific” than Knight’s work?