Transcript Heredity
Gregor Mendel (1822-1884) Known as “The Father of Genetics” copyright cmassengale © Fall 2005, Pflugerville ISD, 7th Grade 1 Who was Gregor Johann Mendel? Austrian monk Studied the inheritance of traits in pea plants Developed the laws of inheritance Mendel's work was not recognized until the turn of the 20th century 2 © Fall 2005, Pflugerville ISD, 7th Grade Who was Gregor Johann Mendel? Between 1856 and 1863, Mendel cultivated and tested thousands of pea plants He found that the plants' offspring retained traits of the parents copyright cmassengale © Fall 2005, Pflugerville ISD, 7th Grade 3 Particulate Inheritance Mendel stated that physical traits are inherited as “particles” Mendel did not know that the “particles” were actually Chromosomes & DNA copyright cmassengale © Fall 2005, Pflugerville ISD, 7th Grade 4 Why did Mendel use pea plants? Can be grown in a small area Produce lots of offspring Produce pure plants when allowed to selfpollinate several generations Can be artificially cross-pollinated copyright cmassengale © Fall 2005, Pflugerville ISD, 7th Grade 5 Mendel and His Peas • Mendel tested 7 traits: 1. 2. 3. 4. 5. 6. 7. Flower color Flower position Seed color Seed shape Pod shape Pod color Plant height http://www.fieldmuseum.org/exhibits/traveling_mendel.htm © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas • Mendel crossed flowers that were truebreeding for each characteristic. • He crossed a purple (PP) flowered plant with a white (pp) flowered plant. (Parent Generation) http://biology.kenyon.edu/courses/biol114/KH_lecture_images/Mendel/Mendel.html © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas • Where did the white color go?? © Fall 2005, Pflugerville ISD, 7th Grade White Parent • The first generation (F1) of plants all had purple flowers. (pp) Purple Parent (PP) (Pp) (Pp) (Pp) (Pp) Mendel and His Pea Plants • In the second generation (F2) he had 3 purple flowered plants, and 1 white flowered plant. © Fall 2005, Pflugerville ISD, 7th Grade Purple Parent (Pp) Purple Parent (Pp) • Mendel took two of his first generation (F1 x F1) purple flowered plants and crossed them together. (PP) (Pp) (Pp) (pp) Mendel and His Peas • Mendel noticed in the first generation, all of the white flowers seemed to disappear. • He called this a recessive trait. • The white color faded into the background at first. • It showed up in the next generation when he pollinated the flowers. © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas • The color (purple) that seemed to mask over the recessive color was named the dominant trait. © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas • Mendel was responsible for figuring out that each plant carried two sets of instructions for each characteristic (one from the “mom” and one from the “dad”). • Like many scientists, his work was not accepted until after his death. © Fall 2005, Pflugerville ISD, 7th Grade Let’s Review 1. If you crossed a true-breeding black rabbit with a true-breeding white rabbit, all of the offspring would be black. Which trait is dominant in rabbits: black fur or white fur? 2. Which trait is recessive? © Fall 2005, Pflugerville ISD, 7th Grade Answer White Rabbit (bb) • The trait for black fur is dominant over the trait for white fur. The white fur trait is recessive. Black Rabbit (BB) (Bb) (Bb) (Bb) (Bb) http://www.buckeyevalleyfarms.freeservers.com/photo.html © Fall 2005, Pflugerville ISD, 7th Grade Science Humor © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas Vocabulary 1. Heredity- the passing of traits from parent to offspring. 2. Self-pollinate- A plant is often able to pollinate by itself because it contains both the male and female reproductive structures. © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas 3. True-breeding- all of the offspring will have the same trait as the parent when self-pollinated 4. First-generation- the very first set of offspring from two parents 5. Dominant trait- the trait observed when at least one dominant allele for a characteristic is inherited © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas 6. Recessive trait- a trait that is apparent only when two recessive alleles are inherited 7. Genes- a segment of DNA that carries hereditary instructions and is passed from parent to offspring 8. Alleles- multiple forms of the same gene © Fall 2005, Pflugerville ISD, 7th Grade Mendel and His Peas 9. Genotype- an organisms inherited combination of alleles. (BB) 10. Phenotype- an organisms inherited appearance (what you see) 11. Homozygous- having two identical alleles for a trait 12. Heterozygous- having two different alleles for a trait. © Fall 2005, Pflugerville ISD, 7th Grade