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 19th 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.