MENDEL’S WORK Key Concepts What were the results of Mendel’s experiments or crosses? What controls the inheritance of traits in organisms?

Key Terms  Heredity  Trait  Genetics  Fertilization  Purebred  Gene  Alleles  Dominant allele  Recessive allele  hybrid

Mendel’s Work  Mendel experimented with thousands of Pea plants looking at their different traits to understand the process of heredity. His discoveries form the foundation of genetics.  Heredity –the passing of physical characteristics from parents to offspring  Trait- each different form of a characteristic  Genetics – the study of heredity

Mendel’s Experiments  Flowering Plant anatomy  Pistil – produces the female sex cells or eggs  Stamens – produce pollen which contains the male sec cells or sperm  Fertilization is when the egg and sperm join forming a new organism  In plants the pollen must reach the pistil for fertilization to occur. This is called pollination

Pollination  Pea plants usually self- pollinate. The pollen from their stamens lands of the same plants pistils.  Mendel developed a method to cross-pollinate pea plants. He took pollen from one pea plant and brushed it onto the pistil of another.

Crossing Pea Plants  Mendel crossed plants with contrasting traits  Ex. Tall plants with short plants  Started with purebred plants – a purebred organism is one who is the offspring of many generations of that have the same trait

The F 1 Offspring  Mendel crossed purebred tall with purebred short Parental (P) generation  Tall x short  Offspring from the cross are called F 1 (filial)  All F 1 offspring were tall

F 2 offspring  When F 1 were full grown, Mendel allowed them to self-pollinate  F 2 were a mix of tall and short  ¾ were tall and ¼ were short

Experiments with OtherTraits  Mendel crossed pea plants with other contrasting traits such as seed shape, seed color, seed coat color, etc.  In all crosses the F1 generation had only 1 form of the trait  In the F2 generation the “lost” form reappeared in ¼ of the plants.

Dominant and Recessive Alleles  Mendel’s Conclusion  factors control the inheritance of traits in peas.  They exist in pairs  The female parent contributes one factor and the male parent contributes the other factor  One factor in a pair can mask or hide the other factor

Genes and Alleles  Genes – factors that control a trait  Alleles – different forms of a gene  An organisms traits are controlled by the alleles it inherits from its parents.  Some alleles are dominant, while others are recessive  Dominant allele – trait always shows  Recessive allele –trait is hidden whenever dominant allele is present

Alleles in Mendel’s Crosses  Stem Height Cross  P generation tall tall x short short  F1 generation all were tall short- Look tall  F2 generation ¼ tall tall - look tall ¼ tall short + ¼ short tall – look tall ¼ short short – look short

Symbols for alleles  Letters are used to represent alleles  Capital letters are used for dominant alleles  Lowercase letters are used for recessive alleles  Purebred tall = TT  Purebred short = tt  Hybrid (one of each) =Tt

Significance of Mendel’s Contribution  Before Mendel most people thought that the traits of an individual were a blend of their 2 parents.  If they blended the Tt plants should be medium height  Mendel found out that traits are determined by individual alleles some of which are dominant and some recessive.  Recessive traits may seem to disappear in the offspring only to reappear in the next generation  Mendel’s work was not recognized during his lifetime, but was rediscovered in He is now considered the Father of Genetics.

Sources      book/Dictionary/Dictionary_C/dictionary_cross_pollination.htm book/Dictionary/Dictionary_C/dictionary_cross_pollination.htm        on.html on.html