Mendelian Genetics: Biology II, Grade 11 STEM Finals

• General Biology II, Grade 11 STEM, 2nd Semester Finals

Mendelian Genetics

• Homozygous Dominant: possessing two dominant alleles, example DD
• Heterozygous: possessing a dominant and a recessive allele, example Dd; the individual shows the dominant phenotype
• Homozygous Recessive: possessing two recessive alleles, example dd
• Phenotype: Observable trait of an individual based on its genotype, examples are red flower, curly hair, etc.
• Phenocopy: A trait expressed due to specific environmental conditions, such as dyed hair
• Identical Twins: Also known as "Monozygotic Twins", derived from a single fertilization event
• Fraternal Twins: also known as "Dizygotic Twins", twins derived from separate fertilization events, resulting in two separate zygotes
• Monohybrid Cross: A cross involving a pair of contrasting traits, mating of two true-breeding individuals
• Two individuals crossed are the parental generation (P1); offspring are the first filial generation (F1)
• Crossing F1 individuals results in the second filial generation (F2); this is called selfing or self-fertilization
• Dihybrid Cross: Genetic cross involving two pairs of contrasting traits, also called a "two-factor cross"
• Punnett Square: A square diagram used to predict genotypes of a particular cross or breeding experiment
• It is named after Reginald C. Punnett, devised the approach in 1905
• Used to determine the probability of an offspring having a particular genotype

Mendel's Four Postulates

• Unit Factors in Pairs: Genetic characters are controlled by unit factors (genes) that exist in pairs
• Dominance/Recessiveness: When two unlike unit factors for a single character are present, one is dominant, the other is recessive
• Law of Segregation: During gametogenesis, paired unit factors separate randomly, each gamete receives one or the other
• Law of Independent Assortment: Two factors (genes) of each contrasting character assort independently of other factors

Pedigree Analysis

• Proband: The individual in the pedigree that led to the construction of the pedigree
• Autosomal Trait: a trait whose alleles are found in the autosomes
• Genotype: The gene pair an individual carries for a trait is symbolized with a pair of letters
  • Uppercase Letter (A) for a Dominant Allele, Lowercase (a) for Recessive Allele

Sex Linkage & Recombination

• Hemophilia: An inherited bleeding disorder; people with hemophilia bleed easily because they do not have enough clotting factors
• Clotting factors are needed for blood to clot to prevent excessive bleeding
• Duchenne Muscular Dystrophy (DMD): A genetic problem that causes muscles to weaken and atrophy
• Hypertrichosis: Long and strong hairs growing from the helix of the pinna
• Webbed Toes: The common name for "Syndactyly", a fusion of two or more digits of the feet
• Linkage: Genes for different characteristics are inherited together more frequently than predicted by probability
• Linked Genes: Found on the same chromosome
• Unlinked Genes: Found on different chromosomes
• Genetic Recombination: The production of offspring with combinations of traits different from either parent
• This occurs during crossing over of homologous chromosomes in Prophase I of meiosis
• Organisms have two sets of chromosomes: autosomes, or chromosomes other than sex chromosomes
• Sex Chromosomes: Chromosomes that carry the genes that determine sex
  • Most organisms including humans have XX = female, XY = male
• Sex Linkage: Genes linked or attached to a sex chromosome
• Sex-Linked Inheritance: A condition in which a gene is located or attached to a sex chromosome, resulting in sexually dependent inheritance

Sex-Linked Traits

• Tendency for certain characteristics to occur predominantly in one sex
• Y Chromosome: Shorter than X chromosome, has fewer genes for traits Some genes are only found on the X or Y chromosome
• Many recessive characteristics on the X chromosome appear more frequently in males
• X-Linked Inheritance: Relates to genes passed on via the X chromosome
• X-Linked Dominant: Alteration in one copy of a gene on the X chromosome can cause the condition in both males and females; affected males tend to have more significant conditions

X-Linked Recessive

• Female = XX (Affected or Non-Affected), carrier is usually not affected
• Male = XY, will be affected by the condition
• Y-Linked: Also called "Holandric Genes", related to genes attached to the Y chromosomes
• X Inactivation: Females have the same effective dose of most X-linked genes
• One X chromosome in each cell in female mammals becomes inactivated during early embryonic development
• Barr Body: The inactive X cell condenses into a compact object, discovered by Murray Barr

DNA Replication

• Deoxyribonucleic Acid: Also known as "DNA"; contains genetic instructions, composed of two strands
• Pairs: Adenine - Thymine (forms two hydrogen bonds); Cytosine - Guanine (forms three hydrogen bonds)
• Ribonucleic Acid: Also known as "RNA", is composed of one strand
• Pairs: Adenine - Uracil; Cytosine - Guanine
• Composition Of RNA Nucleotide: Ribose Sugar, Phosphate Molecule, and One of Four Nitrogenous Bases
• Types Of RNA: tRNA, mRNA, rRNA
• Purines - "Two Organic Rings"
• Pyrimidines - "Three Organic Rings"
• DNA molecule is a double helix polymer
• Each strand has a backbone of sugar + phosphate, DNA is wrapped around Histones
• Nucleosome: DNA is wrapped around Histones
• supercoiling creates compact chromosomes.
• Each chromosome has a million base pairs, 23 chromosomes per cell
• DNA Replication: Allows genetic information to be inherited
• The process of DNA Replication: Initiation, Priming, Polymerization, and Termination

Initiation Stage of DNA Replication

• Unwinding of DNA Strand.
  • Helicase: Unwinds the double helix, disrupts the hydrogen bonds between bases.
  • Creates a replication fork
  • Single-Strand Binding Protein helps prevent the DNA from re-pairing
  • The unwinding causes torsional strain, Topoisomerase breaks, untwists, and reconnects DNA; it is always ahead of the replication fork

Priming Stage of DNA Replication

• Priming: Addition of a small section of RNA
  • RNA Primase: Anneals and synthesizes an RNA Primer at a specific location to begin replication
  • 5' End of Leading Strand and Okazaki Fragment, 5-10 nucleotides long

Polymerization and Termination Stage of DNA Replication

• Polymerization: Building of daughter DNA strand by adding new complementary bases
  • DNA Polymerase III binds to the primer and generates a whole new complementary strand - nucleotides enter the enzymes active site and polymerase catalyzes formation of bond that joins each new nucleotide as it is added to the complementary strand
  • nucleotides are always added to the 3' end of the existing strand not the 5', and strands are antiparellel
• Direction of replication is in opposite directions for the opposing strands Leading Strand: Follows helicase synthesizing one continuous strand of DNA Lagging Strand: Copied one section at a time when more template is available

Termination of DNA Replication

• Termination: Replacing RNA primer by DNA, includes joining the sugar-phosphate backbones

DNA Polymerase I - replaces the primer nucleotides for the DNA nucleotides

• DNA Ligase - joins bonds together

Protein Synthesis

• The Cell and the Genome: The cell is the basic unit of all living tissue
• Nucleus: contains the genome in most human cells, the genome is divided into 23 pairs of chromosomes
• Transcription: DNA -- mRNA - RNA polymerase moves along the DNA, creating messenger RNA
  • Translation: mRNA -- Protein mRNA is read in triplets known as codons and each codon corresponds to an amino acid.
• tRNA delivers the correct amino acid, forming a growing chain

Genetic Engineering

• Also called "Recombinant DNA Technology" or "Genetic Manipulation", is the direct manipulation of an organism's genes using biotechnology
• DNA Cutting + DNA Joining = Hybrid DNA Organism
• Genetically Modified Organisms: Also known as "GMOs” or “Bioengineered Foods", whose DNA has been changed using genetic engineering techniques
• Restriction Enzymes: Enzymes used to create DNA fragments with sticky ends or blunt ends that can join with other DNA fragments
• Plasmid: A small extrachromosomal DNA molecule within a bacterial cell that is physically separated from chromosomal DNA
• Ligation: Joining of two nucleotides, or two nucleic acid fragments
• Vector: Any particle used as a vehicle to artificially carry DNA to another cell
• Biolistics: Projectiles to deliver DNA (Use of a "gene gun" to fire DNA-coated pellets on plant tissues)
• Heat Shock Treatment & Electroporation: Process used to transfer plasmid DNA into bacteria