The Work of Gregor Mendel

Transmission of characteristics from is parents to offspring called. heredity The SCIENCE that studies how those characteristics are passed on from one generation to the next is called Genetics

The Father of Genetics is Gregor Mendel, a monk whose study of genetic traits was the beginning of our understanding about. how genes work

http://hus.yksd.com/distanceedcourses/yksdbiology/lessons/fourthquarter/chapter11/11-1/images/mendelexperiment.gif Mendel designed experiments using Pea plants in the monastery garden MALE part of flower makes Pollen (sperm) FEMALE part of flower makes egg cells http://www.cedarville.edu/academics/education/resource/schools/chca/2scideb/debwebpv.htm

In pea plants, the pollen normally joins with an egg from the same plant (= Self pollinating ) so seeds have ONE parent http://hus.yksd.com/distanceedcourses/yksdbiology/lessons/fourthquarter/chapter11/11-1/images/mendelexperiment.gif

MENDEL S PEA EXPERIMENTS Mendel started his experiments with peas that were true breeding = if allowed to self pollinate they would produce offspring identical to themselves. http://hus.yksd.com/distanceedcourses/yksdbiology/lessons/fourthquarter/chapter11/11-1/images/mendelexperiment.gif

MENDEL S PEA EXPERIMENTS Mendel removed pollen making parts and added pollen from another plant. This allowed him to cross-breed plants with different characteristics and study the results http://hus.yksd.com/distanceedcourses/yksdbiology/lessons/fourthquarter/chapter11/11-1/images/mendelexperiment.gif

A specific characteristic is called a trait Mendel in peas. studied 7 traits Pearson Education Inc,; Publishing as Pearson Prentice Hall

MENDEL S EXPERIMENTS P 1 generation ( ) F 1 generation ( = filial offspring) F 2 parental generation

Principles of Dominance Section 11-1 P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short Go to Section:

When Mendel crossed PURE PLANTS with 2 contrasting traits: (EX: Tall crossed with short) He always found same pattern: 1. ONLY ONE trait showed F 1 in the generation BUT... Missing 2. trait in F 2 3:1 the generation in a ratio returned

PATTERNS ARE THE KEY Image modified from: http://www.laskerfoundation.org/rprimers/gnn/timeline/1866.html http://www.accessexcellence.org/ab/gg/mendel.html

Mendel decided that there must be a pair of FACTORS that each control trait and that one factor must be able to the other. HIDE

We now know that Mendel s factors are genes carried on the pair of homologous chromosomes http://www.emc.maricopa.edu/faculty/farabee/biobk/crossover.gif

DIFFERENTgene CHOICES for a trait are called. ALLELES http://sps.k12.ar.us/massengale/genetics%20tutorial.htm

DOMINANT = An allele HIDES that the presence of another allele RECESSIVE = An allele is hidden by that the presence of another allele

Why did the recessive trait disappear in the F 1 generation and reappear in the F 2? The pattern corresponds to the movement of chromosomes during MEIOSIS Image modified from: http://www.laskerfoundation.org/rprimers/gnn/timeline/1866.html

WHAT DOES MEIOSIS HAVE TO DO WITH IT?

REMEMBER HOMOLOGOUS chromosomes SEPARATE during ANAPHASE I = SEGREGATION Image modified from: http://www.emc.maricopa.edu/faculty/farabee/biobk/crossover.gif

offspring an allele for F 1 received tallness from their TALL parent and an allele for shortness from their SHORT parent. The F 1 plants ALL LOOK TALL carrying but are an shortness allele for Images from: BIOLOGY by Miller & Levine; Prentice Hall Publishing 2006

EXPLAINING the F 1 CROSS LAW OF SEGREGATION alleles are separated when the F 1 plants made gametes When these gametes recombined to make the F 2 generation, the recessive trait reappears in ¼ of the offspring Image from: BIOLOGY by Miller & Levine; Prentice Hall Publishing 2006

Mendel s 3 laws Law of segregation: alleles (chromosomes) are separated into gametes Law of dominance: an organism only needs 1 dominant allele to express the dominant trait Law of independent assortment: alleles are separated randomly/independent of one another