Meiosis, DNA Structure, and DNA Extraction

• Meiosis produces haploid gametes, such as sperm and egg cells, which contain only one copy of each chromosome.
• Meiosis results in the formation of four non-identical cells from one cell.
• The process creates four daughter cells, each with half the number of chromosomes, leading to genetically different haploid gametes.

DNA Structure

• DNA is a polymer composed of two strands coiled into a double helix.
• The strands are linked by complementary base pairs connected by weak hydrogen bonds.
• Nucleotides, consisting of a sugar, phosphate group, and one of four bases, form DNA.
• The four bases are Adenine (A), Cytosine (C), Thymine (T), and Guanine (G).
• A always pairs with T (A-T), and C always pairs with G (C-G).

Genome and Genes

• A genome constitutes the entire DNA of an organism.
• A gene is a section of DNA that codes for a specific protein.

DNA Extraction from Fruit

• Mash the fruit to increase its surface area and mix it with detergent and salt in a beaker.
• Detergent breaks down cell and nuclear membranes, releasing DNA.
• Salt causes the DNA to stick together.
• Filter the mixture to remove debris.
• Add ice-cold ethanol slowly to precipitate the DNA, which is insoluble in cold alcohol.
• The DNA appears as a stringy white precipitate.

Protein Synthesis

• A gene is a DNA section with a specific base sequence that codes for a specific sequence of amino acids.
• Three bases code for a single amino acid (codon).
• The base order controls the order and types of amino acids joined in a polypeptide chain.
• Polypeptide chains form specific proteins.

Types of Proteins

• Completed protein chains fold into unique shapes, enabling specific functions.
• Enzymes act as biological catalysts to speed up chemical reactions.
• Hormones carry messages around the body.
• Structural proteins provide physical structure and strength.

Transcription

• Transcription occurs in the cell nucleus.
• RNA polymerase binds to non-coding DNA in front of a gene.
• DNA strands unzip, and RNA polymerase moves along one strand, using coding DNA as a template to make mRNA.
• Base pairing ensures mRNA is complementary to the gene.
• mRNA moves out of the nucleus and joins with a ribosome.

Translation

• Translation occurs after mRNA binds to a ribosome where a protein can be assembled
• Amino acids are brought to the ribosome by transfer RNA (tRNA).
• The order in which they are brought to the ribosome matches the order of the base triplets in mRNA, also known as codons.
• tRNA contains an anticodon complementary to the mRNA codon, ensuring correct amino acid order.
• Amino acids are joined together by the ribosome to form a polypeptide (protein).

Genetic Variants and Phenotypes

• A mutation is a rare, random change to an organism's DNA base sequence that can be inherited.
• A mutation in a gene produces a genetic variant, which may code for a different amino acid sequence, altering the protein’s shape and activity.
• Altered protein activity can change an organism's phenotype.
• Mutations in non-coding DNA can affect RNA polymerase binding, altering mRNA transcription and protein production, thereby influencing the phenotype.

Gregor Mendel

• Trained in mathematics and natural history
• Observed characteristics passed on to the next generation in pea plants.
• Offspring inherit 'hereditary units' from each parent.
• One unit is received from each parent.
• Units can be dominant or recessive, and cannot be mixed together.
• Mendel's work wasn't recognized until after his death due to the lack of understanding of genes and chromosomes.

Definitions

• Gamete: An organism's reproductive cell (sperm or egg) with half the number of chromosomes.
• Chromosome: A structure in the nucleus made of a long strand of DNA.
• Gene: A short DNA section that codes for a protein, contributing to a characteristic. Most characteristics result from multiple interacting genes.
• Alleles: Different forms of a gene; humans have two alleles for each gene, inherited from each parent.
• Dominant Allele: Only one copy is needed for expression and the phenotype to be observed.
• Recessive Allele: Two copies are needed for expression and the phenotype to be observed.
• Homozygous: Both inherited alleles are the same (two dominant or two recessive).
• Heterozygous: One inherited allele is dominant, and the other is recessive.
• Genotype: The combination of alleles an individual has (e.g., Aa).
• Phenotype: The physical characteristics observed in the individual (e.g., eye color).
• Zygote: The stage of development immediately after fertilization, a diploid (2n) cell formed from the fusion of two haploid gametes.

Alleles

• Different alleles code for different forms of the same protein, leading to differences in inherited characteristics.
• An allele coding for a damaged protein form can cause illness, like Huntington’s Disease, where a misfolded protein results.

Monohybrid Inheritance

• Monohybrid inheritance is the inheritance of characteristics controlled by a single gene.
• It can be investigated using a Punnett square, which shows possible allele combinations in offspring.
• From the combinations, the ratio of these combinations can be worked out.
• The dominant allele is represented by a capital letter while the recessive allele is represented by the same letter in lowercase.

Family Pedigrees

• Family pedigree diagrams trace the inheritance pattern of a specific characteristic through generations.
• They can be to work out the probability of inheriting a genetic disorder.
• Males are squares, females are circles.
• Affected individuals are red, unaffected are blue.
• Horizontal lines indicate parents, with children shown underneath.

ABO Blood Group Inheritance

• Co-dominance is when two dominant alleles are expressed together.
• Multiple alleles is when three or more alleles can be present in the same loci, but, not necessarily all expressed at once.

ABO Blood System

• The ABO blood system expresses multiple, co-dominant alleles for A, B, and O.
• Only two alleles can be expressed at once.
• A and O alleles result in Type A blood.
• A and B alleles result in Type AB blood.
• Two A alleles result in Type A blood.
• Two B alleles result in Type B blood.
• Two O alleles result in Type O blood, making it rarer.

This lesson covers meiosis, the process that produces haploid gametes. It also explains DNA structure, including its double helix shape, base pairs, and nucleotide composition. Lastly, it describes how to extract DNA from fruit.