Chapter 4 Mendel’s Work Section 1

Gregor Mendel  Mid nineteenth century  Priest named Gregor Mendel  Worked in a garden at a monastery  Heredity:  Heredity: the passing of physical characteristics from parents to offspring

Why do pea plants have different characteristics?  Traits:  Traits: physical characteristics  Examples: stem height (tall or short), seed color (green or yellow) TRAITS  Pea plant TRAITS were often similar to those of their parents and sometimes they were different GENETICS  His studies laid the foundation for GENETICS – the scientific study of heredity

Mendel’s Experiments  The flower’s petals surround the pistils and the stamens  Pistil:  Pistil: produces female sex cells, or eggs  Stamen:  Stamen: produce pollen, which contains male sex cells, or sperm  Fertilization :  Fertilization : new organisms can form when the egg and the sperm join in this process

Self-Pollinating  Pea plants are usually self-pollinating  Pollen from a flower lands on a pistil of the same flowerCross-Pollinating  “crossed”  Mendel removed pollen from a flower on one plant, then brushed the pollen onto a flower on a second plant

Crossing Pea Plants  How are you going to study the inheritance of traits in pea plants?  Mendel decided to “cross” plants with contrasting traits  Example:  Example: tall plants with short plants  He started with purebred plants  Purebred:  Purebred: an organism is the offspring of many generations that have the same trait

The F1 and F2 Offspring Mendel crossed purebred tall plants with purebred short plants ---This is called the parental generation, or the P generation F1 offspring are all tall ---The offspring from this cross are the first filial generation, or the F1 generation He then allowed for the F1 offspring to self- pollinate F2 offspring are tall and short ---The offspring from this cross are the second filial generation, or the F2 generation

Results of a Cross P generation (one tall, one short) F1 generation (both tall) F2 generation (mix of tall and short)

 What other traits did Mendel study?  Pod color, seed shape, flower position  What were the two forms of the seed shape?  Round and wrinkled

Genes and Alleles  Genes:  Genes: factors that control a trait  Alleles:  Alleles: different forms of a gene  An organism’s traits are controlled by alleles it inherits from its parents. Some alleles are dominant, while others are recessive

Dominant Alleles vs. Recessive Alleles  Dominant Allele: an allele whose trait always shows up in the organism when the allele is present  Recessive Allele: an allele that is masked when a dominant allele is present

Let’s do some math…. Examples for Stem Height  One recessive allele + one dominant allele = dominant traits (tall stem)  One recessive allele + one recessive allele = recessive traits (short stem)

Alleles in Mendel’s Crosses  Combination of Alleles:  Hybrid tall---  Hybrid tall--- one allele for tall stems and one allele for short stems (one dom, one rec)  Purebred tall---  Purebred tall--- two alleles for tall stems (two dom)  Purebred short---  Purebred short--- two alleles for short stems (two rec)

Symbols for Alleles  Geneticists use letters to represent alleles  Dominant allele  Dominant allele is represented by a capital letter  Example: tall stems = T  Recessive allele  Recessive allele is represented by a lowercase letter  Example: short stems = t

 2 dominant alleles for tall stems = TT  2 recessive alleles for short stems = tt  1 recessive allele for short stems and 1 dominant allele for tall stems = Tt

Significance of Mendel’s Contribution  The importance of Mendel’s discovery was NOT recognized during his lifetime  Then, in 1900, three scientists discovered his work  They quickly realized the importance of his work Father of Genetics  Mendel is often called the Father of Genetics