Gregor Mendel  19 th century priest  Tended to gardens in a monastery  Worked with pea plants and heredity

Heredity  Passing of physical characteristic from parents to offspring  Mendel wondered why different pea plants had different physical characteristic

Pea Plants  Characteristics Tall vs. Short Green seeds vs. Yellow seeds Round shape vs. Wrinkled shape Pg 79

Traits  Each form of the characteristics is called a trait  Traits are often similar to parents  However, sometimes they are different from the parents

Genetics  Mendel’s work led to the foundations of genetics  Genetics is the scientific study of heredity

Mendel’s Experiments  Cross pollinate pea plants  Crossed plants with contrasting traits  Started with purebred organisms Purebred: offspring of many generations that have the same trait

F1 Offspring  F1 offspring is the first filial generation or offspring of a parent generation  Parent generations or P generation Usually purebreds

Mendel’s F1 Generation  P generation was purebred tall plant crossed with a purebred short plant  Mendel’s F1 generation all where tall plants  The short trait seemed to disappear!!

Mendel’s F2 Generation  Self pollinated his F1 generation  F2 (second filial) where both tall and short plants  ¾ were tall and ¼ were short  Remember the parents where both tall

Experiments with traits  In F1 generations only 1 form of the trait showed  In F2 generations the “lost” trait showed in ¼ of the plants

Reasoning  Each parent contributes a trait to the offspring  One factor can mask or hide another factor  Example: tall will mask short

Genes and Alleles  Genes are the factors that control a trait  Alleles are different forms of genes

Alleles  In pea plants, the gene that controls stem height has 2 alleles 1 for tall (T) 1 for short (t)  Gets 1 allele from each parent TT Tt or “tT” tt

Dominant vs. Recessive  Traits are controlled by alleles inherited from parents  Some alleles are dominant and other are recessive  If dominant allele is present you will have that trait (recessive is trumped by dominant)  Recessive alleles will only show if dominant allele is not present

In Pea Plant  Tall is dominant  TT = tall  Tt = tall  “tT” = tall  tt = short

Mendel’s F1  P generation were purebred, both alleles are the same TT and tt  F1 generation all have Tt One from each parent  All plants are tall because they all have the dominant allele

Mendel’s F2  Cross F1 plants or self pollinate them  Outcomes 2 dominant alleles = TT = tall 1 dominant allele = Tt or “tT” = tall 0 dominant alleles = tt = short

Symbols for Alleles  Letters represent alleles  Dominant Allele = capital letter  Recessive allele = lowercase letter  If different alleles dominant is first