Mendel's Pea Plant Experiments

• Heredity is passing traits from parents to offspring and genetics studies DNA, genes, variation, and heredity
• Sexual reproduction shows heredity as it has lots of inherited characteristic variation
• Gregor Johann Mendel, the "Father of Genetics" experimented on pea plants (Pisum sativum) from 1856-1863
• Mendel's experiments led to the laws of inheritance

Mendel's Pea Plant Experiments

• Mendel chose seven distinct pea plant traits: seed color, seed shape, flower color, and plant height
• Mendel began with purebred plants, which consistently showed one trait over generations to avoid mixed genetic information
• Mendel performed cross-pollination, transferring pollen from the anther (male) of one plant to the stigma (female) of another, controlling mating
• The offspring (F1 generation) showed only one parental trait, indicating dominance
• Mendel allowed F1 plants to self-fertilize, creating the F2 generation
• Mendel analyzed the F2 generation, observing traits controlled by dominant and recessive alleles followed specific ratios

Results of Mendel's Experiments

• Mendel crossed pure tall and short pea plants
• The F1 generation were all tall with no dwarf plants
• The F2 generation were 3 tall offsprings for every 1 dwarf offspring
• Similar results occurred with other characters Mendel studied
• Mendel saw only one parent's characteristics in the F1 generation
• The F2 generation showed the other parent's characteristics as well
• Traits in the F1 generation are called dominant, while those appearing first in the F2 generation are recessive

Mendel's Conclusions

• Genes exist in pairs called alleles, passed from parents to offspring
• Homozygous alleles are the same, while heterozygous alleles are different
• Capital letters denote dominant characters (TT for tallness) and lowercase letters recessive (tt)
• Heterozygous genes (Tt) can appear tall but carry a recessive gene for future generations
• Phenotype is the plant's appearance, while genotype is its genetic makeup
• A plant with Tt genes appears tall (phenotypically) and has a recessive gene
• During gametogenesis, chromosomes halve in gametes, resulting in a 50% chance of either allele fusing with the other parent's allele to form a zygote

Mendel's Laws

• Law of Dominance: Offspring exhibit the dominant trait, expressing only the dominant allele
• Law of Segregation: Chromosome copies separate, causing alleles to segregate; traits do not mix in a hybrid pair
• Law of Independent Assortment: Genes for different traits are inherited independently, as they reside on different chromosomes

Information Transfer

• Genetic information is transferred from one generation to the next using DNA or RNA
• DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) carry biological information

DNA

• Most organisms use DNA, but some viruses use RNA as genetic material
• Watson and Crick discovered DNA's double helix structure, made of nucleotides
• The backbone consists of phosphates connected to deoxyribose, a five-carbon sugar
• DNA includes a phosphoric acid, deoxyribose sugar, and a nitrogenous base consisting of purines (adenine and guanine) and pyrimidines (cytosine and thymine)
• Adenine pairs with thymine via double hydrogen bonds
• Cytosine pairs with guanine via triple hydrogen bond
• Helices are bound due to hydrogen bonds

RNA

• RNA differs from DNA, as a single-stranded genetic material
• RNA has nucleotide bases similar to DNA, however uses uracil instead of thymine, pairing with adenine
• While DNA is the genetic material in most organisms, RNA is found in a only a few viruses
• tRNA (transfer RNA) transfers amino acids from mRNA to ribosomes
• mRNA (messenger RNA) carries codes for amino acids from DNA to ribosomes
• rRNA (ribosomal RNA) is found on ribosomes and helps in protein synthesis, as a component of the ribosome

Transcription, Translation, and Translocation

• Transcription: mRNA is synthesized per the nucleotide sequence of DNA
• The nucleotide sequence in DNA codes genes that control structure and function
• Information for protein synthesis is stored in nucleotide sequences of DNA
• Central Dogma: protein synthesis by DNA through RNA
• DNA Transcription to RNA Translation to Protein

Transcription

• Genetic information encoded in DNA synthesizes RNA molecules, specifically mRNA
• DNA serves as a template for complementary mRNA strands in the cell nucleus
• RNA polymerase catalyzes DIR INA by matching complementary RNA nucleotides to the DNA template

Translation

• mRNA information builds a corresponding protein
• Transfer RNA (tRNA) molecules bring amino acids to the ribosome, which facilitates linkage through codons (three-nucleotide sequences)
• Genetic code dictates how triplets translate into amino acids, with each codon corresponding to a specific amino acid or a start/stop signal
• Codon AUG initiates translation, while UAA, UAG, and UGA are the stop codons which end the process

Translocation

• In genetics, translocation involves moving a chromosomal segment from one location to another
• Genetic Translocation: Occurs between non-homologous chromosomes or within the same one, leading to disorders or genetic diversity
• Cellular Translocation: Molecules/structures move within a cell, e.g., proteins move into organelles, using the central dogma of molecular biology
• Transcription synthesizes mRNA, translation synthesizes proteins, and translocation moves genetic material

Chromosomes

• Chromosomes in eukaryotic cells consist of DNA and proteins, carrying genetic information as genes
• Chromosome numbers/structure vary by species
• Humans have 23 pairs of chromosomes (46 total): 22 pairs of autosomes and 1 pair of sex chromosomes
• Females have XX and males have XY chromosomes
• Chromosomes divide into two arms via a centromere: 'p arm' (short) and 'q arm' (long)

Chromosomal Disorders

• Caused by the change in chromosome number/structure
• Humans typically have 46 chromosomes (23 pairs)
• A duplicated chromosome is called trisomy, and a non-duplicated chromosome is called monosomy
• A duplicated set of chromosomes is called triploidy, and more duplication results in polyploidy

Syndromes

• Down's syndrome: Trisomy of chromosome 21 characterized by intellectual disability and heart conditions
• Turner's syndrome: Missing second sex chromosome (XO) characterized by mental disabilities and retarded sexual development
• Klinefelter's syndrome: Extra sex chromosome (XXY) and is similar to Turner's
• Edward's syndrome: Trisomy of chromosome 18
• Patau's syndrome: Trisomy of chromosome 13

Diseases by Chromosome Structure Alterations

• Deletion: Loss of a chromosome portion
• Duplication: Part of a chromosome duplicates resulting in repeat gene sequences
• Translocation: Portion of a chromosome moves to another (reciprocal or robertsonian)
• Inversions: Gene sequence of an inverted portion appearing inverted

Mutations

• Mutation causes sudden changes in genetic material, resulting in offspring differences, mutations in nucleotides
• Mutations are minor and major, and genetic disorders like sickle cell anemia occur
• Necessary process leading to evolution

Benefits of Heredity Science

• Diagnoses hereditary disorders
• Treats incurable hereditary disorders
• Prevents heredity disorders
• Creates hybrid animals and plants
• Uses industrial microbes

Evolution

• Earth History has various evolution theories including Lamarck's and Darwin's
• Evolution explains flora/fauna distribution
• Evolving transforms simple states through natural processes
• Evolution changes naturally like Earth's surface, oceans, and animals
• Ancient people believed modern animals/plants always existed
• Fifth century BC Xenophane showed differences in past/present organisms
• Democritus, Aristotle, Linnaeus, Buffon, Lamarck, Darwin, Weismann, and Hugo de Vries studied biological evolution with Lamarck and Darwin being the most popular

Lamarck's Theory of Evolution

• Lamarck stated that traits acquired from responding to environmental changes are passed down
• Differences occur between plants in different environments, which change the needs of orgamisms
• Adaption can cause an increase/decrease in organ use, unused organs become extinct, and all traits are passed down

Lamarck's Doctrines

• Influence of Environment: Organisms change as conditions change
• Organ Transformatio: Transformation is possible with increased need
• Law of use and disuse of organs: Organs become strong with use
• Inheritance of acquired characters: Traits get passed down
• Origin of new species: Traits lead to species creation

Examples of Lemarck's Theory

• Birds' skin developed with constant swimming
• Giraffe's necks grew to eat leaves off of trees in recent generations
• Ostrich wings became endangered as a result of disuse
• Snakes lost their chameleon legs because of continued misuse underground

Criticism of Lemarck's Theory

• Scientists said those altered traits cannot get inherited with experiments
• Drosophila couldn't birth blind flies after 60 generations
• Weismann cut rats tails for 22 generations without tailless births

Darwin's Theory of Evolution

• Darwin traveled Islands and developed Darwinism/natural selection theory
• According to Darwin, reproduction occurs at an excessive rate, causing geometric increases and habitat has limited surface area
• Struggle for existence includes intra/interspecific struggle for living things
• Earth lacks two of the same, as even children are both different
• Continued struggles cause transmitted variations
• Smaller changes are responsible for the emergence of different species

Darwanism

• Survival of the fittest causes others to become extinct
• Most important aspect is natural selection with chosen organisms breeding and inheriting favorable varieties
• Differences get greater, and new species are born
• Critcism includes: Darwin only discussed surviving fitness
• Natural selection leads to organism emergence
• Unexplained theory of extinction
• Only mutual struggle has been discussed of new offspring
• Existence of organs that don't help

Darwinism vs Lamarckism

Microbial Heredity/Evolution

• Central to diversity/adaptation
• Focuses on exchange, mutation, and selection in microbial
• Microorganisms adapt unlike higher organisms
• Vertical Gene Transfer Passes genetic information from parent to offspring
• Horizontal Gene Transfer Acquires Lateral Genes

Mechanisms of Microbial Evolution

• Catalysts is at the core of evolution because of spontaneous mutation
• Some mutations help, and natural selection prevails with bacteria and viruses
• High turnover rates allow for quick evolutionary respinse to environmental change

Natural Selection

• Microbial populations adapt, shaping their genetic composition
• Experience selective pressures, favoring individuals adapted to environments
• Fitness refers to surviving and reproducing with natural selection refining the microibal population

Genetic Drift

• Mechanims described as random
• Unlike natural selection where the traits are based on adaptive traits, genetic drift is driven by chance and random
• This can lead to a complete loss of alleles
• Experiencing fluctuations in size, genetic drifts becomes important
• When a small subset of individuals establishes a new population this is what causes this shift
• Without more pressures, alleles become dominant

Antibiotic Resistance

• Resistance evolves in response to antibiotics
• Genetic resistance is through Horizontal Gene Transfer, Mutations, and Mobile Genes elements
• Resistent microbes survive better that propagation of it, which helps in Microbial evolution

Definitions

• Gene: Basic unit of inheritance, a sequence of DNA that can mutate (can have 2 or more alternative forms)
• Alleles: Alternative forms of genes affecting traits
• Chromosomes: Thread-like nucleic acid structures (DNA and proteins) where genes are located
• Genotype: Complete heritable genetic identity
• Phenotype: Expressed form
• Dominant Alleles: Affects phenotype
• Recessive Alleles: Is a recessive allele
• Homozygous: Where alleles are the same
• Heterozygous: Alleles are different