Student Text Pages 76-81

I. Mendel’s experiments Left Hand Activity Finish A. crossing pea plantsFilling in the information. B. C. D. II. A. B. C. D

What were the results of Mendel’s experiments, or crosses? Mendel’s work was the foundation of genetics, the scientific study of heredity.  Gregor Mendel was curious about the different forms of characteristics, or traits, of pea plants.

Johann Mendel “Father of Modern Genetics” Johann became a Monk and name was changed to Gregor. Studied plants and pea plants genetics.

 Heredity is the passing of physical characteristics from parents to offspring.  Genetics is the scientific study of heredity.  Trait is a characteristic that an organism can pass on to its offspring through its genes.  Genes are the set of information that controls a trait; a segment of DNA on a chromosome that codes for a specific trait.

Mendel’s Experiments  Pea plants are usually self- pollinating, meaning pollen from a flower lands on the pistil of the same flower.  Mendel develop a method by which he cross-pollinated, or “crossed,” pea plants.

 A new organism begins to form when egg and sperm join in the process called fertilization.  Fertilization is the process in which an egg cell and a sperm cell join to form a new organism.  Before fertilization can happen in pea plants, pollen must reach the pistil of a pea flower through pollination.

Mendel’s Fertilization of Pea Plants

 Mendel crossed two pea plants that differed in height. He crossed purebred tall plants with purebred short plants.  These parent plants, the P generation, were purebred because they always produced offspring with the same trait as the parent.

 In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation.  However, in the F2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants.

 From his results, Mendel reasoned that individual factors, one from each parent, control the inheritance of traits. Today, scientists call the factors that control traits genes.  The different forms of a gene are called alleles.

Answer the questions to the study guide. All pages

What controls the inheritance of traits in organisms? An organism’s traits are controlled by the alleles it inherits from its parents.  Some alleles are dominant, while other alleles are recessive.

Dominant and Recessive Alleles  A dominant allele is one whose trait always shows up in the organism when the allele is present.  Recessive allele is an allele that is masked when a dominant allele is present.

 A recessive allele is hidden whenever the dominant allele is present.  A trait controlled by a recessive allele will only show up if the organism does not have the dominant allele.

Dominant Genes and Recessive Genes

 In Mendel’s cross, the purebred tall plant has two alleles for tall stems.  Purebred is the offspring of many generations that have the same trait.

 The purebred short plant has two alleles for short stems.  The F1 plants are all hybrids: they have two different alleles for the trait—one allele for tall stems and one for short stems.  Hybrid is an organism that has two different alleles for a trait: an organism that is heterozygous for a particular trait.  Geneticists use a capital letter to represent a dominant allele and a lowercase version of the same letter for the recessive allele.

 Mendel’s discovery was not recognized during his lifetime. In 1900, three different scientists rediscovered Mendel’s work.  Because of his work, Mendel is often called the “Father of Genetics.”

Students are to reread Pages Answer questions 1-2 all parts.