The Work of Mendel

Heredity: the passing of traits from parents to offspring Genetics: Study of heredity Traits -inherited characteristics

Gregor Mendel was the first person to predict how traits are transferred. Austrian monk who studied garden peas. He is known as the “Father of Genetics”.

Why did he use peas? -Reproduce sexually -Gametes in the same flower -Fertilization could be controlled -readily available (in his garden)

Mendel transferred pollen from plant to plant and then studied resulting peas. Studied only one trait at a time.

The first pair of plants that he crossed were the “P 1 ” (parental) generation. The offspring of that cross he called the “F 1 ” (first filial) which in Latin means “son”.

Seed Shape Flower Position Seed Coat Color Seed Color Pod Color Plant Height Pod Shape Round Wrinkled Round Yellow Green Gray White Smooth Constricted Green Yellow Axial Terminal Tall Short YellowGraySmoothGreenAxialTall Mendel’s Seven F 1 Crosses on Pea Plants

Genes -chemical factors that determine traits. -Segment of DNA part of a chromosome. Alleles - the different forms of a gene. Example: yellow/green

The principle of dominance states that some alleles are dominant & others recessive.

Dominant traits: exhibited trait, written with 1 or 2 capital letters Example: Y Recessive traits: inhibited trait, written with recessive letters (lowercase letters) Example: y

Mendel’s Law of Segregation  Two alleles for each trait separate during meiosis.  During fertilization, two alleles for that trait unite.

Phenotypes & Genotypes Phenotype: appearance of an organism Example: short, tall, green, yellow Genotype: gene combination of an organism Example: tt, TT, Tt, yy, YY

Heterozygous: the 2 alleles are different Example: Yy -heterozygous (also called hybrid) Homozygous: the 2 alleles are the same (also called purebred) Example: YY means homozygous dominant, and yy means homozygous recessive

Monohybrid Crosses Crosses that differ by a single trait Example: yellow seed pea plant x green seed pea plant The first generation produced offspring resembling only one parent Example: all yellow seeds

The second generation produced: 3/4 of peas had yellow seeds 1/4 of peas had green seeds Mendel concluded that each trait has 2 factors (which are now called alleles). Inherit one allele from MOM and one allele from DAD. (Egg & sperm)

Punnett square- a diagram used to predict gene combinations.

Probability: the chance or percentage of chance of a trait being exhibited (The likelihood that a particular event will occur.)

Law of Independent Assortment  Random distribution of alleles occurs during gamete formation  Genes on separate chromosomes sort independently during meiosis.  Each allele combination is equally likely to occur.

Section 11-2 Tt X Tt Cross Go to Section:

Section 11-2 Tt X Tt Cross Go to Section: