Genetics and Molecular Biology

• Study notes on Genetics and Molecular Biology

Gene & Allele

• Genes are segments of DNA contain instructions for making proteins that determine traits.
• Alleles are different versions of a gene that result in variations of a trait.

Nucleic Acids

• Nucleic acids consist of a sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base (A, T/U, G, C).
• Nucleic acids store and transfer genetic information and guide protein synthesis.

DNA Molecule

• DNA has a double helix structure composed of two strands.
• The sugar-phosphate backbone provides stability, while nitrogenous bases (A-T, G-C) are held together by hydrogen bonds.
• Adenine (A) pairs with Thymine (T) in DNA, while Guanine (G) pairs with Cytosine (C).
• In RNA, Uracil (U) replaces Thymine (T).

DNA Replication & Repair

• Helicase unzips the DNA strands during DNA replication.
• DNA polymerase adds complementary bases.
• Ligase seals the gaps between newly formed DNA fragments.
• DNA polymerase proofreads to fix mistakes.
• Mismatch repair corrects incorrectly paired bases.
• Excision repair removes and replaces damaged DNA segments.

RNA Molecule

• RNA plays a role in protein synthesis.
• mRNA (messenger RNA) carries genetic information from DNA to the ribosome.
• tRNA (transfer RNA) brings amino acids to the ribosome for protein assembly.
• rRNA (ribosomal RNA) helps form ribosomes and catalyzes protein synthesis.
• RNA is single-stranded, uses uracil (U) instead of thymine (T), and contains ribose sugar instead of deoxyribose.

Central Dogma of Molecular Biology

• Transcription (DNA → mRNA) occurs in the nucleus.
• RNA polymerase reads DNA and creates a complementary mRNA strand during transcription.
• Translation (mRNA → Protein) occurs in the ribosome.
• Ribosomes read the mRNA and use tRNA to assemble amino acids into proteins during translation.

Mutations

• Mutations are permanent changes in DNA sequence.
• Silent mutations have no change in the protein.
• Missense mutations change one amino acid, possibly altering protein function.
• Nonsense mutations create a premature stop codon, resulting in a shortened protein.
• Insertions add one or more nucleotides, while deletions lose one or more nucleotides.
• Frameshift mutations shift the reading frame, often causing major changes.

Meiosis

• Meiosis occurs in the testes to produce sperm in males and in the ovaries to produce eggs in females.
• Meiosis reduces chromosome number by half (from diploid to haploid) to ensure genetic diversity.

Key Concepts

• Haploid (n) is one set of chromosomes (gametes).
• Diploid (2n) is two sets of chromosomes (body cells).
• Sister chromatids are identical copies of the same chromosome, connected at the centromere.
• Homologous chromosomes are a pair of chromosomes (one from each parent) with genes for the same traits.
• Crossing over, occurring during Prophase I, is the exchange of genetic material between homologous chromosomes.

Steps of Meiosis

• Chromosomes condense, homologous pairs form, and crossing over occurs during Prophase I.
• Homologous chromosomes line up in the center of the cell during Metaphase I.
• Homologous chromosomes separate and move to opposite poles during Anaphase I.
• Two haploid cells form during Telophase I.
• Chromosomes condense again during Prophase II.
• Chromosomes align in the middle during Metaphase II.
• Sister chromatids are pulled apart during Anaphase II.
• Four haploid daughter cells form during Telophase II.

Meiosis in Males vs. Females

• Meiosis in males produces four sperm cells.
• Meiosis in females produces one egg and three polar bodies.

Reproduction & Development

• Study notes for the processes of reproduction and development

Male Reproductive System

• The path of sperm is: Testes → Epididymis → Vas Deferens → Urethra.
• Seminal vesicles provide fructose for energy.
• The prostate gland produces alkaline fluid to neutralize acidity.
• The bulbourethral gland provides lubrication.

Female Reproductive System

• The path of eggs: Ovary → Fallopian tube → Uterus

Developmental Stages

• Cleavage is rapid cell division without growth.
• Blastula formation is where a hollow ball of cells form.
• Gastrulation is the formation of three germ layers.
• Neurulation leads to the development of the brain and spinal cord.

Pregnancy Trimesters

• Organ systems develop during the first trimester.
• Fetal growth and minor development happens during the second trimester.
• The nervous system and lungs mature during the third trimester.

Birth Process

• The cervix opens during dilation.
• The baby is delivered during expulsion.
• The placenta is expelled during the placental stage.

Mendelian Genetics

• Study notes on understanding Mendelian Genetics.

Key Terms

• Genotype means the genetic makeup (e.g., AA, Aa, aa).
• Phenotype is the physical expression of a trait.
• Homozygous means two identical alleles (AA or aa).
• Heterozygous means two different alleles (Aa).
• Dominant refers to a trait expressed if one allele is present.
• Recessive refers to a trait expressed only if both alleles are recessive.

Mendel’s Laws

• The law of segregation means that alleles separate during gamete formation.
• The law of independent assortment means that traits are inherited independently.