Cellular Division: Mitosis and Meiosis

• Cellular division governs the creation of new cells.

Two Types of Cells

• Somatic cells are body cells that are diploid and undergo mitosis.
  • Mitosis results in two identical daughter cells.
• Germ cells are gametes that are haploid and undergo meiosis.
  • Meiosis results in four individual gametes (sex cells), containing half of the parent cell's genetic material

Cell Cycle

• Cells spend most of their time in interphase; metaphase is brief.
• G1 and G2 are growth phases where the cell prepares for division.
  • G1 involves the growth of cytoplasm and cellular structures.
  • G2 involves the duplication of centrioles.
• The synthesis phase involves DNA replication using chromatin.
  • This phase ends with two sister cell chromatids connected by a centromere.
• The M phase includes mitosis and meiosis.

Mitosis

• Prophase involves centrioles migrating and forming spindle fibers.
• Metaphase involves spindle fibers attaching to kinetochores at the equatorial plate.
• Anaphase involves spindle fibers pulling.
• Telophase involves cytokinesis, involving either a cleavage furrow (in animal cells) or cell plate formation from the center outward (in plant cells).

Meiosis

• Meiosis results in four unique daughter cells.
• All daughter cells have only one copy of each chromosome.

Meiosis I

• Prophase 1 includes homologous chromosomes aligning to form tetrads.
• Crossing-over of genetic material occurs.
• Metaphase 1 includes spindle fibers attaching.
• Anaphase 1 includes spindle fibers pulling homologous chromosomes apart.
• Telophase 1 results in two diploid daughter cells.

Meiosis II

• Prophase 2 involves DNA not being replicated.
• Metaphase 2 includes spindle fibers attaching to kinetochores.
• Anaphase 2 includes spindle fibers pulling.
• Telophase 2 includes cytokinesis, resulting in four unique haploid daughter cells.
• When two gametes merge, a zygote forms, which then uses mitosis to grow.

Chromosomes and Reproduction: Central Dogma

• Transcription involves DNA being read to make mRNA.
• Translation involves RNA being decoded to make proteins.
  • A gene is the recipe for one protein.
  • a gene is a piece of DNA that codes for a protein and a gene gets expressed when the protein it codes for is produced.

Central Dogma: Transcription

• DNA is double-stranded, while RNA is single-stranded.
• DNA pairs include:
  • A pairs with U
  • C pairs with G
  • G pairs with C
  • T pairs with A
• mRNA is produced based on the DNA template.
  • DNA unzips, and mRNA makes a pairing strand.
• In translation, a protein is produced based mRNA sequence.
  • DNA undergoes transcription to produce mRNA, which is then translated into a protein.
• A codon is a set of three nucleotides that encodes one amino acid.

Gene Code

• A codon consists of 3 nucleotides or nitrogenous bases.
• Exons code for proteins.
• Introns do not code for proteins.
  • I.e. Stop codon.
• DNA is transcribed into mRNA, which is then translated into proteins.
  • The RNA codon table is a reference guide for translation.

Mutations

• Mutations are damages to DNA.
  • Damaged DNA is frequently recognized and repaired or triggers apoptosis.
• Of all DNA, only about 2% are genes, that code for protiens.
• Many mutations are non-coding
• Mutations can be caused randomly, by age, environmental agents (radiation, sunlight, chemicals like tobacco), lifestyle factors (smoking, high fat diet), and viruses (HPV).
• Acquired mutations are not inherited
• Inherited mutations are present at birth.
• Mutations can cause disease or lead to cancer,
  • e.g., PKU (phenylketonuria) results from a missing liver enzyme that breaks down phenylalanine.
  • Problems can be avoided by maintaining a diet low in phenylalanine.

Use of Genetics to Identify Individuals

• Each person has a unique genetic code, differing by less than 1%, except for identical twins.
• Variation (polymorphism) makes each person's DNA profile unique, like a fingerprint.
• Restriction Fragment length polymorphisms can be used to create a DNA fingerprint!

Gel Electrophoresis

• Separates of DNA based on size, charge, and shape in a gelatin-like material using an electrical field.
  • DNA is negatively charged and moves toward the positive side.
  • Shorter DNA fragments move faster than larger ones.

Applications of DNA Fingerprinting

• Paternity Testing

  • A child's DNA fingerprint can be compared to its know mother's and the possible father's.
  • Half of a child's DNA belongs to its mother and half to the father.

• Crime Scene Investigation

  • DNA collected from a crime scene is compared to suspects to look for an exact match.

• Pedigree analysis uses the following notation:

  • XX indicates female
  • XY indicates male.

• Nucleic Acids

  • Deoxyribose Nucleic Acid (DNA)
  • Ribose Nucleic Acid (RNA)

• All life has at least DNA or RNA.

• Nucleic acids contain genetic informatio and execute processes accordingly.

  • I.e. Hormone and Protein Production

• Monomers of nucleic acids: Phosphate, Sugar, Nitrogenous Base

• Nitrogenous bases are classified as:

  • Purines (two-ringed Adenine, Guanine)
  • Pyrimidines (one ringed Thymine, Cytosine)

• DNA base pairings:

  • A-T
  • G-C

• Trait/Phenotype: is a physical characteristic encoded by a gene (what you see).

• Genes: segment of chromosomes that encode traits (genetic material in the chromosomes).

  • the same set of genes are on each chromosome
  • The version of the gene can be different.

• Alleles: one of several different alternatives of a gene

• Genotype: genetic composition of an organism; actual alleles of each genes carried by the organism.

• The Law of Segregation: two alleles for a gene must seperate during meiosis.

• Homozygous: same version of alleles, homozygous dominant or homozygous recessive. (BB or bb)

• Heterozygous: two different version of the alleles also known as hybrid (Bb)

• Dominant: the allele that determines the individuals phenotype in heterozygous.

  • the phenotype associated with the other allele is hidden.

• Punnett Square Method: a way to predict the genotypes and phenotypes of offsrping.

  • Shows statistics of potential outcomes of a genetic cross.

• Genotypic raio: actual genetic makeup and how alleles are combined.

• Phenotypic ratio: outward appearance from a combination of alleles/gene types.

• Incomplete Dominance: The dominant allele doesnt completely block the phenotype of the recessive allele.

• Phenotype looks like a blend between the two.

• Co-dominance: Both alleles act dominant and can both be expressed at the same time.

• Sex-linked Crosses: the genes are on the X or Y chromosomes.

  • Women are XX and Men are XY.