Biology Chapter: Chromosomes and Protein Synthesis

Chromosomes are long, thread-like structures made of DNA that house the genetic instructions necessary for the development and functioning of an organism. Genes, which are segments of DNA, provide the codes to produce specific proteins essential for various biological processes. Alleles represent the different forms of a gene, which contribute to the diversity in traits among individuals. The determination of biological sex is based on the presence of X and Y chromosomes, with females typically having two X chromosomes (XX) and males having one X and one Y chromosome (XY).

DNA and Protein Synthesis

• DNA controls cell functions by directing protein production (enzymes, carriers, receptors).
• DNA has two strands with four nucleotides (AT and CG).
• Messenger RNA (mRNA) has AU and CG bases.
• Protein synthesis occurs in the cytoplasm, outside the nucleus.
• Protein synthesis has two stages: transcription and translation.
• Transcription rewrites DNA's base code into mRNA's base code.
• Translation uses mRNA's base sequence to build amino acids into a protein.
• The gene remains in the nucleus while mRNA copies it.
• mRNA is produced in the nucleus and moves to the cytoplasm.
• mRNA passes through ribosomes.
• Ribosomes assemble amino acids into proteins.
• The specific mRNA base sequence determines the amino acid order.
• All cells in an organism possess the same genes, but not all genes are expressed in each cell.

Cell Division: Mitosis

• Mitosis is a nuclear division producing genetically identical cells.
• Mitosis is essential for growth, repair of damaged tissues, and replacement of worn-out cells and asexual reproduction in plants.
• Chromosomes replicate before mitosis.
• During mitosis, replicated chromosomes separate, maintaining the chromosome number.

Cell Division: Meiosis

• Meiosis is a reduction division (diploid to haploid) creating gametes (sperm and egg).
• Meiosis produces genetically varied cells.
• Gametes are produced by meiosis.

Monohybrid Inheritance

• Inheritance is the transmission of genetic information.

• Genotype is an organism's genetic makeup (e.g., Tt or GG).

• Phenotype is an organism's observable traits (e.g., tall plant or green seed).

• Genotype + environment + variation → phenotype

• Homozygous means having two identical alleles (e.g., TT or gg). Homozygous individuals are pure-breeding.

• Heterozygous means having two different alleles (e.g., Tt or Gg).

• Dominant alleles are expressed when present.

• Recessive alleles are expressed only if no dominant allele is present.

Pedigree Diagrams

• Pedigree diagrams track a characteristic's inheritance through generations.
• Pure breeding means an individual is homozygous for a trait.
• Diagrams determine the probability of inheriting a genetic disorder.

Genetic Diagrams

• Punnett squares show possible allele combinations in offspring.
• Dominant alleles are represented by capital letters, recessive by lowercase.
• Choose clear, different capital and lower case letters.

Modification of Mendelian Genetics

Codominance

• Codominance occurs when two alleles are equally dominant (e.g., 50%).
• Both alleles are expressed in the heterozygote phenotype.
• Example: If parents have red and white phenotypes, offspring may have both colours.

ABO Blood Group

• ABO blood group inheritance demonstrates codominance and multiple alleles.
• Three alleles (IA, IB, IO) determine blood type.
• IA and IB are codominant, both dominant to IO.

Sex-Linked Characteristics

• Sex-linked characteristics involve genes on sex chromosomes.
• X-linked recessive traits are often more common in males than females.

Explore the fascinating world of chromosomes, genes, and proteins in this quiz on biology. Learn about the structure of DNA, the role of chromosomes in genetics, and the complex process of protein synthesis. Test your understanding of key concepts such as transcription and translation, as well as the importance of amino acid sequences.