Inheritance, DNA & RNA: Genetic Material

Inheritance Overview

• Inheritance is the study of how traits are passed from parents to offspring

Genome

• The genome is the entire genetic material of an organism

DNA

• DNA is a double helix formed of two strands linked by paired bases

Gene

• A gene is a short section of DNA that codes for a specific protein and controls our characteristics

Chromosome

• Chromosomes are long strands of DNA coiled with histone proteins in the nuclei

DNA and RNA

• Base pairs in DNA and RNA include adenine, thymine, guanine, cytosine, and uracil
• DNA is deoxyribonucleic acid, a double helix polymer containing genetic information
• DNA contains genes and is found in chromosomes in the nucleus of cells
• DNA is a polymer made from nucleotides (monomers)
• DNA consists of deoxyribose sugar (pentose) + phosphate + base (A-T, G-C)
• The sequence of bases in DNA controls the sequence of amino acids made

RNA

• RNA is ribonucleic acid, a single-stranded molecule responsible for protein synthesis
• RNA consists of ribose sugar + phosphate + base (A-U, G-C)
• The function of RNA is to transfer code in DNA out of the nucleus to ribosomes in the cytoplasm

Protein Synthesis

• Transcription involves DNA being transcribed onto an mRNA (messenger RNA) molecule
• The DNA helix is untwisted and unzipped in the nucleus by the enzyme DNA helicase
• Hydrogen bonds between complementary base pairs are broken during this process
• mRNA matches to its complementary base on the strand and moves out of the nucleus
• Translation involves the ribosome translating mRNA into proteins
• mRNA attaches to a ribosome that reads its bases in codons (groups of three)
• Start/stop codons in mRNA signal where the code for a protein begins and ends
• A codon codes for a specific amino acid, and tRNA has matching anticodons
• tRNA brings amino acids to the ribosome, which join when the base pairs on codons and anticodons match, forming a chain of amino acids
• A protein is released and folded to form its structure when the stop codon is reached

Genotype and Phenotype

• Genotype is the combination of alleles that control each characteristic
• Phenotype is the physical characteristic that can be seen or found

Allele Interactions

• A dominant allele's phenotype is expressed regardless of whether the genotype is homozygous or heterozygous; it only needs to be inherited once
• A recessive allele needs to be inherited from both parents for its characteristic to show up in the phenotype
• Codominance is the equal expression of equally dominant alleles in the phenotype

Homozygous and Heterozygous

• Homozygous refers to when the two alleles of a gene are the same
• Heterozygous refers to when the two alleles of a gene are different

Polygenic inheritance

• Polygenic inheritance occurs when phenotypes are controlled by more than one gene
• It allows for a wide range of combinations of phenotypes, such as height

Monohybrid Inheritance

• Monohybrid inheritance occurs when phenotypes are controlled by a single gene

Genetic Diagrams

• A Punnett square shows combinations of alleles in offspring, with the dominant allele shown first
• A family pedigree traces the pattern of inheritance of characteristics through generations

Mitosis and Meiosis

• Mitosis involves cell division that produces two genetically identical diploid daughter cells
• Mitosis occurs in growth and repair of cells, cloning, and asexual reproduction
• Mitosis is for replacement of cells or growth, not reproduction
• The process of mitosis undergoes one division
• A cell grows and all 46 chromosomes are replicated (96 chromosomes)
• The cell divides and the chromosomes are split, forming the daughter cells
• Meiosis involves cell division that produces four genetically different haploid daughter cells
• Meiosis occurs in the formation of gametes and increases genetic variation
• Meiosis is only used to make sperm and egg cells
• The process of meiosis undergoes two divisions
• A cell grows and all 46 chromosomes are replicated (96 chromosomes)
• The cell divides into two cells, each with 46 chromosomes
• The two cells then divide into four haploid cells, each with 23 chromosomes

Variation

• Variation refers to differences in DNA sequences of individuals within the same species
• Gametes are genetically different due to meiosis
• Random fertilization of gametes increases genetic variation
• Genetic variation means phenotypes depend on inherited alleles from parents
• Environmental variation refers to characteristics caused by differences in lifestyle, climate, or diet, such as accents, scars, or in plants, the amount of sunlight, minerals, water, etc
• Combined, genes decide inherited characteristics, while the environment affects how they develop

Mutations

• Mutations are rare, random, spontaneous changes in genes (DNA) that can be inherited
• Mutations can occur in any chromosome
• Mutations alter the base pair sequence in DNA, which can code for different proteins
• This leads to different proteins being made, which affects the phenotype
• The effects of mutations are most often none, rarely have a small effect and extremely rarely a significant effect
• Mutations are rare
• The codon codes for the same amino acid anyway
• It occurs in a recessive allele
• The mutation occurs in a minor section of DNA that does not code for anything obvious or important

Increased Mutation Rates

• Increasing mutation rates can be caused by ionizing radiation or chemical mutagens
• These damage bonds and cause changes in base sequences
• Increased rates of mutation can cause cells to become cancerous

Natural Selection

• Evolution is the cumulative change in the genetic makeup of a population over many generations
• The theory of evolution is based on the concept of natural selection

Variation and Survival

• There is variation within species, caused by different genes from sexual reproduction and mutations
• Some phenotypes will give individuals a survival and reproductive advantage
• Individuals are more likely to pass their genes on at a higher rate
• Repeated over generations, the advantageous phenotype becomes the norm

Antibiotic Resistance

• Antibiotics are chemicals that kill or inhibit growth and reproduction of bacteria
• Antibiotic resistance occurs when bacteria become resistant to antibiotics
• Bacteria reproduce and evolve in short time spans
• Variations caused by mutations can cause bacteria to be resistant
• Resistant bacteria do not die when treated with antibiotics and reproduce with less competition, passing on their genes for antibiotic resistance
• The whole population of bacteria becomes antibiotic resistant
• Causes of antibiotic resistance include unnecessary overuse of antibiotics, such as treating non-serious infections, failing to finish a prescribed course, or routine use in agriculture
• The effect is that it becomes harder to find working antibiotics, and infections become harder to control
• Always finish a course of antibiotics; otherwise, the worse bacteria will be left and reproduce, becoming resistant to that antibiotic