Genetics – Patterns of Inheritance Gregor Mendel – 1822-1884 Austria Monk in Brün (now Brno, Czech Rep.)

Important points regarding Mendel’s methods Chose traits with two clearly contrasting character states. Did controlled cross-breeding and carried them on for at least two generations. Mathematical rigor, high replication.

Mendel’s observations One characteristic is dominant and one is recessive. All F1 show dominant characteristic. ¾ of F2 show dominant characteristic, ¼ recessive.

Mendel’s Explanation – The law of segregation Each individual carries two copies of a gene for each characteristic. Each individual passes on one copy of the gene to each offspring. The offspring receives one copy of the gene from each parent. Genes are not changed during the individual’s lifetime.

Biological basis for Mendel’s law of segregation Genes are on chromosomes. Diploid individuals have 2 copies of each gene. These are not necessarily identical copies, they may be alleles (alternative forms of a gene). Meiosis separates them; each gamete carries one copy.

Vocabulary Gene – information that codes for a particular trait. Alleles – alternative forms of a gene. Genotype – the particular alleles that an individual has. Phenotype – the expression of those genes in the living organism (form, anatomy, chemistry, behavior, etc.) Homozygous – having two of the same allele. Heterozygous – having two different alleles.

How to tell a homozygous dominant from a heterozygote. Both show the identical dominant phenotype. Do a Test Cross. Mate with a homozygous recessive. If the unknown was hom. dom., all offspring will show the dominant phenotype. If the unknown was heterozygous, the offspring will be ½ dominant, ½ recessive.