Mendelian Genetics

Gregor Mendel, “The Father of Genetics” Mendel was interested in why offspring resembled their parents His work was the first to effectively utilize quantitative methods in the study of heredity (inheritance) – the transmission of genetic material from parent to offspring

Genetics genetics – the branch of biology that studies heredity Characteristics that are inherited are called traits Mendel was the first person to succeed in predicting how traits are transferred from one generation to the next

Mendel and his pea plants Why pea plants? 1. Several traits exist in two clearly different forms (example: purple or white flowers) 2. The plants reproduce sexually – two different sex cells, or gametes, are united (fertilization) to create a new organism  Pea plants can self-fertilize (offspring is produced using the reproductive organs of one plant) or they can be cross pollinated (fertilization between two plants)

Mendel and his pea plants 3. Pea plants are small, grow easily, mature quickly, and produce many offspring  significance: Mendel was able to collect a lot of data

Mendel’s Monohybrid Crosses Mendel worked with true breeding plants – if allowed to self pollinate they produce offspring with identical traits (to the parents)  The first trait Mendel studied was height

The First Generation Mendel crossed tall pea plants with short pea plants (P (parental) generation)  He found that all the off spring were tall plants (F1)

The Second Generation Next Mendel crossed plants from the F1 generation (all tall plants)  He observed that the newest generation (F2) had a ratio of 3 tall plants to 1 short plant (3:1, 75% tall and 25% short)

Mendel’s Conclusions 1. Biological inheritance is determined by factors that are passed from one generation to the next.  Today, scientists call the factors that determine traits genes  Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting form  the different forms of a gene are called alleles

Mendel’s Conclusions 2. Principle of Dominance  some alleles are dominant and some are recessive  An organism with a dominant allele for a particular form of a trait will always have that form  An organism with a recessive allele for a particular form of a trait will only have that form if a dominant allele for the trait is not present