Introduction to Genetics

Introduction to Genetics

• Genetics is important to individuals, society, and the study of biology
• Genetic variation is the difference in the characteristics of individuals within a species

Alleles and Genotype

• An allele is an alternative form of a gene
• Different alleles can produce differences in the observable features (phenotype) of an organism
• The set of alleles for a given trait carried by an organism is called the genotype
• Thomas Hunt Morgan used the fruit fly (Drosophila melanogaster) to study genetics

Dominant vs. Recessive

• A dominant allele is expressed even if it is paired with a recessive allele
• A recessive allele is only visible when paired with another recessive allele

Chromosomes

• Every gene has its place (locus) on a chromosome
• Genotype is the combination of alleles found in an organism
• Phenotype is the visible expression of the genotype
• Wild-type phenotype is the most common or generally accepted standard
• Mutant alleles are usually recessive

DNA Structure

• DNA is a double helix molecule composed of two strands held together by hydrogen bonds between the nitrogen-containing bases
• The backbone of the DNA strand is composed of alternating sugar-phosphate molecules
• Adenine (purine) makes hydrogen bonds with thymine (pyrimidine)
• Cytosine (pyrimidine) makes hydrogen bonds with guanine (purine)
• The bonding between the nitrogen-containing bases in DNA is referred to as complementary base pairing

Nucleic Acids

• Nucleic acids are polymers of nucleotides
• Two varieties of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)
• DNA stores genetic information and is responsible for preserving, copying, and transmitting information within cells and from generation to generation
• RNA performs a wide range of functions within cells, including protein synthesis and regulation of gene expression

Structure of a Nucleotide

• Each nucleotide is composed of three parts: a phosphate group, a pentose sugar, and a nitrogen-containing base
• There are five types of nucleotides found in nucleic acids
• DNA contains adenine, guanine, cytosine, and thymine, while RNA contains adenine, guanine, cytosine, and uracil