Genetics: Pedigree Analysis & Key Terms

Genetics: Pedigree Analysis

• A pedigree chart diagrams the inheritance of a trait or health condition through generations of a family.
• "Phenylketonurics" are individuals who suffer from Phenylketonuria (PKU), having difficulty metabolizing phenylalanine.

Genetics

• Genetics studies genes which carry information passed from one generation to the next.

Terminologies

• Allele: A variant form of a gene (Dominant and Recessive); An allele is dominant when it effectively overrules the other recessive allele.
• Dominant Allele: An allele expressed if present in the genotype.
• Recessive Allele: An allele whose expression is masked by a dominant allele.
• Genotype: An individual's allele combination for a particular gene (Letters).
• Phenotype: An observable characteristic or physical appearance.
• Homozygous: Possessing identical alleles of one gene.
  • BB (Homozygous Dominant) or bb (Homozygous Recessive) ONLY
• Heterozygous: Possessing different alleles of one gene.
  • Bb (Heterozygous), the dominant allele's characteristics are shown.
• True-Breeding: Homozygous; self-fertilization yields offspring identical to self for a given trait.
• Hybrid: Heterozygous; self-fertilization yields offspring different to self for a given trait.

The Punnett Square

• Monohybrid Cross: Crosses only one trait.

Other Crosses

• Dihybrid Cross: Crosses two traits.

Pedigree Charts

• Male (Square) vs. Female (circle)
• Affected (shaded) vs. Unaffected (unshaded) individual
• Marriage/mating line (line connecting mates) vs. Sibship line (line connecting siblings)
• Fraternal twins (one birthline branching out into the individual twin) vs. Identical twins (same as fraternal twins but with a horizontal bar connecting the branches)
• Generation (Roman Numerals) vs. Individuals in the same generation, counting left to right (designated by Hindu-Arabic numerals)
• Proband (Arrow)

Pedigree Construction Practice

• Pedigree practice involves representing family relationships and traits through pedigree charts.

The Law of Segregation

• F1 Parents: Contain two separate copies of each hereditary factor, (either DOMINANT or RECESSIVE).
• Factors separate when gametes form, with each gamete carrying only one copy of each factor.
• Random fusion of all possible gametes occurs upon fertilization.

The Law of Independent Assortment

• Each pair of factors segregates (assorts independently) of other pairs.
• All possible combinations of factors can occur in the gametes.

Sex-Linkage and Recombination

• Sex-Linked Trait: The gene (pair) that determines a character (e.g., hemophilia) is located on the sex chromosomes.
• X-Linked Trait: A sex-linked trait where the gene or allele for the trait is found on the X chromosome.
• Y-Linked Trait: A sex-linked trait where the gene or allele for the trait is found on the Y chromosome.
• Sex-Influenced Trait: Any trait in a diploid organism whose expression is affected by an individual's biological sex.
  • A trait occurs at a higher frequency in one sex over the other.
• Sex-Limited Trait: Any trait in a diploid organism whose expression is limited to just one biological sex.

What is Sex-Linked Trait?

• The gene (pair) that determines a character (e.g., hemophilia) is located on the sex chromosomes.
  • Females have two X chromosomes, while males have one X chromosome and one Y chromosome.
• For X-linked traits, the allele on the X chromosome is shown as a letter attached to the X Chromosome.

What is Sex-Influenced Trait?

• Autosomal traits appear in both sexes but are expressed to a different degree in each.
  • It seems to act as dominant in one sex and recessive in the other.
• Hormonal or physiological differences between the sexes cause differences in the expression of certain genes (e.g., Male Pattern Baldness, Length of index finger, body hair, muscle mass).
• There are traits that occur in both sexes but can appear at a certain level: for example,, baldness is more prevalent in males since males have higher levels of testosterone.

What is Sex-Limited Trait?

• Sex-limited traits have genes that occur in both sexes (autosomes) but are normally expressed only in the gender having the appropriate hormonal determinant
  • There are traits that occur in specific sexes such as milk production or beard in males.
• It does not occur in all members of that sex.
• Hormonal or physiological differences between sexes may limit the expression of some genes to one biological sex only.

Comparison of Three (Traits)

• Sex-Linked: Found on the SEX CHROMOSOME!
• Sex-Influenced: Affected by an individual's BIOLOGICAL SEX! (differs in the degree of expression).
• Sex-Limited: Limited to just ONE BIOLOGICAL SEX.

Modifications to Mendel's Classic Ratios (Non-Mendelian)

• Co-Dominance: A type of inheritance in which two versions (alleles) of the same gene are expressed separately to yield different traits in an individual.

Gene Interaction

• Incomplete Dominance: Form of gene interaction in which both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype or blending of alleles.
• Multiple Alleles: When there are more than two types of alleles for a given locus or trait, there will result in more than two kinds of phenotypes that may be expressed for that trait.

Mendelian vs. Non-Mendelian Genetics

• Mendelian Inheritance: Genes and their corresponding traits are passed from parents to offspring by means of dominant and recessive alleles.
• Non-Mendelian Inheritance: The pattern of inheritance in which the two alleles are neither dominant nor recessive.

Incomplete Dominance Crossing

• A cross is performed to determine the genotypes and phenotypes of offspring.

Codominance Crossing

• Illustrates the genotypes and phenotypes resulting from the combination of alleles.

Multiple Alleles Crossing

• Explores the inheritance patterns when multiple alleles are involved.

Molecular Structure of DNA, RNA, and Proteins

• Polymer: A long chain molecule made up of a repeated pattern of monomers. The repeating unit is called a monomer.

Nucleic Acids

• Each nucleotide is made up of three components:
  • Nitrogenous Base
  • a pentose [fivecarbon] sugar
  • a phosphate group.
• Two nucleotides are bonded by a phosphodiester bond – which links the phosphate group of 1 nucleotide and the sugar of another nucleotide.
• DNA molecule has two strands of polynucleotides forming a double helix shape in an antiparallel orientation (complementary).
  • One pyrimidine and one purine are always partnered with each other

Base Pairings

• The two strands of DNA are linked together by hydrogen bonds between paired bases.
• Pairing a purine with a pyrimidine results in a uniform diameter for the helical shape of DNA.

Types of Proteins and Their Functions

• Enzymatic Proteins:
  • Function: Selective acceleration of chemical reactions
  • Example: Digestive enzymes catalyze the hydrolosis of bonds in molecules.
• Defensive Proteins:
  • Function: Protect Against diseases.
  • Example: Antibodies inactivate and help destroy viruses and bacteria.
• Storage Proteins:
  • Function: Storage of Amino Acids
  • Example: Casein, the protein of milk, is the major source of amino acids for baby mammals.
• Transport Proteins:
  • Function: Transport of substances
  • Hemoglobin, the iron-containing protein of vertebrae blood, carries oxygen from the lungs to other parts of the body. Other proteins transport molecules across membranes.
• Hormonal Proteins:
  • Function: Coordination of organism's activities (production of hormones)
  • Example: Insulin, secreted by the pancreas, causes other tissues to take up glucose, regulating blood sugar concentration.
• Receptor Proteins:
  • Function: Response of a cell to chemical stimuli
  • Example: Receptors built into the membrane of a nerve cell detect signaling molecules released by other nerve cells.
• Contractile and Motor Proteins:
  • Example: Motor proteins are responsible for the undulations of cilia and flagella.
  • Actin and Myosin proteins are responsible for the contraction of muscles.
• Structural Proteins:
• Function: Support
• Example: Keratin is the protein of hair, horns, feathers, and other skin appendages.
• Collagen and elastin proteins provide a fibrous framework in animal connective tissues.

Structure of Proteins

• The structure of a protein is analogous to a long strand of yarn to the shape that can be knit from the yarn, and to the appearance of the sweater made by the yarn.
• Primary Structure: The primary structure of a protein is its sequence of amino acids.
• Secondary Structure: Proteins can fold and align themselves into Alpha-helix and Beta-pleated sheets (with repeating pattern).
• Random Coils: Do not have repeating patterns
• Tertiary Structure: The 3D arrangement overall shape of a polypeptide resulting from the interactions between the side chains of the various amino acids.
  • 3D = Tertiary
• Quaternary Structure: The overall protein structure that results from the aggregation of these polypeptide subunits.
• Hemoglobin transports oxygen in red blood cells and is a protein with quatrernary structure.

DNA, RNA, and Proteins

• Genes along the DNA molecule direct the synthesis of RNA molecule which aid in the synthesis of polypeptides forming proteins.

The Central Dogma

• Translation, transcription, replication

DNA Replication

• DNA replication: The process on which more DNA is created.
  • Two copies of DNA (Conservative copies: one original and one new DNA strand).
  • Eukaryotic cells: Replication occurs in the nucleus and happens before mitosis/meiosis (interphase)
  • Semi-conservative Replication: One of the two old strands of DNA is conserved or present in each daughter molecule.
  • DNA Elongates in 5' to 3' Direction - Nucleotides add only to the 3' carbon end of a strand, never to the 5'
  • DNA Replication is Semi-Discontinous
  • The LEADING STRAND (3’ to 5’) is synthesized in a continuous manner (5’ to 3’). The LAGGING STRAND (5’ to 3’) is produced discountinously in short chunks called Okazaki fragments.

Enzymes Involved in DNA Replication

• HELICASE (Unzipping Enzyme) → Unzips or separates the two strands of DNA
• DNA POLYMERASE (The Builder) → Replicates DNA molecules to build a new strand of DNA.
• PRIMASE (The initializer) → Makes the primer (starting point) of replication)
• LIGASE (The gluer) → Helps glue DNA fragments together.

Steps in DNA Replication

• Helicase separates the strands during unwinding
• Single-strand binding proteins (SSBP) prevent the unwound strands from rejoining
• Topoisomerase unwinds the double helix so it lays flat
• Primase (Initlizer → primer) makes a short stretch of RNA on the DNA template
• DNA polymerase adds DNA nucleotides to the RNA primer → continues the process
• Leading (continous strand) synthesizes continues in a 5' to 3' direction
• Discontinous synthesis of the lagging strand produces Okazaki fragments since its not continuous
• After RNA primer is replaced with DNA nucleotides, Ligase glues fragments together.

Types of RNA

• mRNA (Messenger RNA): Carries the genetic information that specifies a protein.
• tRNA (Transfer RNA): Carries amino acid to the ribosome, which transfers amino acids to match the correct mRNA codon.
• rRNA (Ribosomal RNA): Forms the ribosome where the site of protein synthesis occurs.

DNA Transcription (DNA - mRNA)

• Transcription: The process in which DNA is copied (transcribed) to mRNA takes place in the nucleus,
  • Cytosine (C) pairs with Guanine (G)
  • Uracil (U) pairs with Adenine (A)

Steps in Transcription

• Initiation: RNA polymerase binds to a region of a gene called the Promoter and DNA unwinds exposing the RNA.
• Elongation: RNA Polymerase adds RNA nucleotides in a 5' to 3' direction.
• Termination: RNA polymerase reaches the terminator gene signaling the release of the new mRNA strand and the removal of the enzyme to the DNA template.

DNA Translation (mRNA - tRNA)

• Translation: The process where the information carried in mRNA molecules is used to create proteins, which, takes place in the cytoplasm(ribosomes).
• The specific sequence of nucleotides in the mRNA molecule provides the code for the production of a protein with a specific sequence of amino acids.
• tRNA has ANTICODONS to match mRNA CODONS

Steps in Translation

• Initiation: The small ribosomal subunit attached to the messenger RNA (MRNA).
• Elongation: The polypeptide chain increases in length one amino acid at a time.
• Termination: A protein complex called a release factor binds to the stop codon and cleaves the polypeptide from the last tRNA

Genetic Engineering & Biotechnology

• Classical breeding uses interbreeding to produce desirable traits through selected properties
• Selective breeding (under classic breeding) to created desirable traits.

Selective Breeding

• A process used by humans to develop new organisms with desirable traits or characteristics.
• Selective breeding in plants leads to generation of new types of foods from same ancestral plant source.
• Selective breeding generates different bread based on the diversity of the food

Genetic Engineering

• Molecular techniques modify traits with the use of a specific target.
• Introduction: New traits introduced to increase desired gene and undesired gene.
• Biotechnology pertains to the manipulation of organisms to create useful products.

Recombinant DNA Technology

• Recombinant DNA: A molecule containing DNA from two different sources
• Transgenic organism receives recombinant DNA.

Plasmid Insertion

• Biolistics: Gene Gun is used to fire small metal particles coated into plant tissues.
• Heat Shock Treatment of 42 c for 1 minute causes the core size of its cell membrane to open.
• Electroporation is expansion of the membrane ores through high intensity electric shock.

DNA Plasmids

• Technique used to separate DNA fragments of desired organisms from other DNA according to the size.

Genetic Engineering to Detect Cancer

• Technique used for the amplification of the sample to detect illnesses.

Genetically Modified Organisms

• Bacteria enhanced to promote health of plants through genetic engineering.
• Plants development to reduces waste from food spoilage.
• BT Corns Enhanced thru biotechnology to protect against pests
• Animals Biotechnology technique have been developed to insert genes into the eggs of animals.