Introduction to Genetics

Heredity Every living thing – plant or animal, microbe or human being – has a set of characteristics inherited from its parent or parents. Since the beginning of recorded history, people have wanted to understand how that inheritance is passed down from generation to generation. Most recently however, scientists have begun to unravel the mysteries that make each person unique. As a result, genetics, the scientific study of heredity, is now at the core of a revolution in understanding biology.

Gregor Mendel The work of an Austrian monk named Gregor Mendel was important to understanding biological inheritance Mendel carried out his work with ordinary garden peas. He knew that part of each plant produces pollen, which contains the plant’s male reproductive cells – sperm. Similarly, the female portion of the plant produces eggs. During sexual reproduction, male and female reproductive cells join, a process known as fertilization.

Gregor Mendel

Mendel’s Garden

Gregor Mendel When Mendel took charge of the monastery garden, he had several stocks of pea plants These peas were true breeding, meaning that if they were allowed to self-pollinate, they would produce offspring identical to themselves. Mendel wanted to produce seeds by joining male and female reproductive cells from two different plants.

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Genes and Dominance Mendel studied seven different pea plant traits. A trait is a specific characteristic such as seed color or plant height, which varies from one individual to the other. Mendel crossed plants with each of the seven contrasting characters and studied their offspring. Mendel called each original pair of parents the P (parental) generation and their offspring the F1 generation.

Genes From his experiments, Mendel concluded that biological inheritance was determined by factors that are passed down from one generation to the next. Today, scientists call these factors GENES Since sexual reproducing organisms have two parents, then they have two forms of the same gene – one from each parent

Genes These alternate forms of genes are called alleles If both alleles from each parent are the same, then it is said to be homozygous (dominant or recessive) IF they are different, then it is said to be heterozygous

Genotype vs. Phenotype An individual’s genetic make-up is known as the genotype The physical characteristics resulting from an individual’s genetic make-up is known as the phenotype.

Summary of Mendel’s Principles The inheritance of biological characteristics is determined by individual units known as genes In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. The dominant gene is the one that is expressed.

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