Biology: Genetic Variation and Breeding

Biology: Genetic Variation and Breeding

# Gene (DNA)

• Definition: A gene is a segment of a DNA molecule that carries the coding information for a specific product (polypeptide chain or DNA molecule).

• Structure:

• The basic building block of DNA is a nucleotide.

• There are four types of nucleotides: A (adenine), T (thymine), G (guanine), and X (xanthine).

• A gene has a double helix structure.

• The template strand of the gene is read in the 3′ -> 5′ direction.

• Genetic Code:

• With four types of nucleotides, there are a maximum of 64 codons (4^3 = 64).

• The start codon is AUG.

• The stop codons are UAA, UAG, and UGA.

• In prokaryotes, the start codon AUG encodes the amino acid formylmethionine.

• In eukaryotes, the start codon AUG encodes the amino acid methionine.

# DNA Replication Process

• Takes place in: The nucleus of the cell.

• Complementary Principle: Nucleotides between the two strands of a DNA molecule bind to each other according to the principle: A binds to T, G binds to X.

• Semi-Conservative Principle: During replication, the mother DNA only transmits 50% of its genetic material to its offspring.

# Transcription (mRNA synthesis)

• Definition: The process of synthesizing RNA from the template strand of a gene.

• Types of RNA:

• Messenger RNA (mRNA)

• Transfer RNA (tRNA)

• Ribosomal RNA (rRNA)

• Reading direction: 5′ -> 3′.

• Building block: 4 types of ribonucleotides (A, U, G, X).

• Size:

• Length: Lnu = Lrnu = 3.4 Angstrom.

• Mass: Mnu = Mrnu = 300 Da.

# Translation

• Definition: The process of protein synthesis.

• Building block of protein: Amino acids.

• Size:

• Length: Laa = 3 Angstrom.

• Mass: Maa = 110 Da.

• Takes place in: Cytoplasm.

# Genetic Code

• Characteristics:

• Read from a specific point.

• Universality: All species share a common genetic code.

• Specificity: A codon encodes only one amino acid.

• Degeneracy: Multiple codons encode the same amino acid.

# Regulation of Gene Activity

• Definition: Regulating the amount of gene product produced in each cell of the body.

• Levels of regulation:

• Transcriptional regulation: Regulating the amount of mRNA.

• Translational regulation: Modifying the protein.

# Genetic Variation

Genetic variation is the changes in the genetic material of an organism, leading to differences in phenotype.

# Breeding

Breeding is the process of selecting and breeding individuals with good genotypes to create plant and animal breeds with high productivity, good quality, and adaptation to environmental conditions.

Note: This is a brief introduction to some basic concepts in biology. To better understand these concepts, you should seek further information through specialized materials.