AP Biology Unit 5: Genetics Simplified

Welcome to our exploration of DNA structure and replication!DNA is made up of four nucleotide bases that pair together in a specific way.Adenine pairs with Thymine through two hydrogen bonds.Guanine pairs with Cytosine through three hydrogen bonds.These base pairs are connected by a sugar-phosphate backbone, forming the famous double helix structure.During DNA replication, the double helix is unwound by an enzyme called helicase.DNA polymerase then adds complementary nucleotides to each separated strand.Finally, DNA ligase seals any gaps in the sugar-phosphate backbone.This process results in two identical DNA molecules, each containing one original strand and one new strand.Now that we understand DNA structure and replication, we're ready to explore how this genetic information is used to make proteins.Gene expression begins with transcription, where RNA polymerase reads the DNA template strand.As RNA polymerase moves along the DNA, it creates a complementary messenger RNA strand.The initial mRNA transcript contains both exons, which code for proteins, and introns, which are removed during splicing.Through splicing, introns are removed and exons are joined together to form the mature messenger RNA.Translation occurs at the ribosome, where the genetic code is converted into protein.Transfer RNAs, or tRNAs, bring specific amino acids to match the codons in the messenger RNA.Each three-letter codon in the messenger RNA specifies a particular amino acid or a start or stop signal.As translation proceeds, amino acids are linked together to form a growing protein chain.Let's examine how traits are inherited using Punnett squares.In this example, we have two parents with genotype Bb. The capital B represents the dominant allele, while lowercase b is recessive.When we combine these alleles, we get four possible genotypes: BB, Bb, Bb, and bb.Now let's look at a more complex example: blood type inheritance.Blood types show codominance, where both A and B alleles can be expressed together.Genetic variation is also created through the process of meiosis, particularly during crossing over.During crossing over, homologous chromosomes exchange genetic material, creating new combinations of genes.This exchange creates new combinations of alleles, increasing genetic diversity.Finally, let's examine how environmental factors can influence gene expression.Factors like temperature, nutrition, stress, and light can all affect how genes are expressed, even when the DNA sequence remains the same.