Heredity, Genetics and DNA Understanding the CODES

Genetics Vocabulary Genetics is the study of heredity, a study of how certain characteristics are passed on from parents to children. Gregor Mendel, an Austrian monk, discovered the basic principles of heredity in the 19 th century.

The science of biological inheritance Genetics

A segment of a chromosome that produces a particular trait. Gene

A pair of hereditary factors that make up a gene (different forms of a gene) Alleles

A hereditary factor that “takes over” the gene determining the trait Dominant Allele

A hereditary factor that is hidden by a dominant allele Recessive Allele

Two identical alleles for a particular trait. TT Homozygous

Two different alleles for a particular trait. Tt Heterozygous

The genetic makeup of an organism due to the genes present Genotype

A particular physical appearance produced by genes Phenotype

Male and female sex cells Gametes

A fertilised seed Zygote

The display of all the chromosomes in a cell’s nucleus Karyotype

Genes Each trait – an expressed characteristic is produced by a pair of hereditary factors collectively know as GENES. Within a chromosome, there are many genes, each of which controls the inheritance of a particular trait. A GENE is a segment of a chromosome that produces a particular trait. For example, in pea plants, there’s a gene on the chromosome that holds the code for seed coat color.

Alleles A gene usually consists of a pair of hereditary factors called alleles. Each organism carries two alleles for a particular trait, one from the mother and one from the father. Another way to say this is that two alleles make up a gene, which in turn produces a particular trait.

Dominant & Recessive Alleles Dominant and RECESSIVE ALLELES: an allele can be DOMINANT or RECESSIVE. A Dominant allele – takes over. Written with a CAPITAL letter. (T) A Recessive allele – hidden by the dominant. Written with a LOWERCASE letter. (t)

Phenotype and Genotype When discussing the physical appearance of an organism we refer to its phenotype. When talking about the genetic makeup of an organism we refer to its genotype. The genotype tells us which alleles the organism possesses.

HOMOZYGOUS and HETEROZYGOUS When an organism has two identical alleles for a given trait, we say the organism is homozygous. For instance TT and tt would both represent the genotypes of homozygous organisms, one homozygous dominant, and one homozygous recessive. If an organism has two different alleles for a given trait, say Tt, that organism is heterozygous.

PARENT and FILLIAL GENERATIONS The first generation is always called the parent or P1 GENERATION. The offspring of the P1 generation are called the first fillial or F1 generation. The offspring of the F1 generation are called the F2 generation.

Mendel’s Law of Heredity 1.Law of Segregation – states that the members of each pair of alleles separate when gametes are formed. A gamete will receive one allele or the other. 2.Law of Independent Assortment – states that two or more pairs of alleles segregate independently of one another during gamete formation.