Intro to Biology

• Evolution is not a progressive force that created the human brain from a simple bacterium.
• Life on Earth is cellular, with the exception of bacteria.
• Life on Earth can be divided into eukaryotes and prokaryotes.

Chromosomes

• Chromosomes are thread-like structures in the cell nucleus made of DNA and proteins, serving as packages of genetic material.
• Chromosomes contain genes that code for proteins and RNA.
• Humans have 46 chromosomes organized into 23 pairs (22 pairs of autosomes and 1 pair of sex chromosomes).
• Gametes (sperm and egg cells) contain 23 chromosomes.
• Human cells are diploid, containing two complete sets of chromosomes, one from each parent.
• Each pair of chromosomes includes one from the mother and one from the father.

DNA

• DNA stores genetic information in a double-helix shape.
• DNA comprises two strands of nucleotides with a sugar-phosphate backbone.
• The four DNA base pairs are adenine (A) with thymine (T) and cytosine (C) with guanine (G).

DNA Replication and Information Flow

• DNA replication copies DNA, ensuring genetic material is passed to daughter cells, essential for growth, tissue replacement, and repair.
• Only 2% of DNA codes for proteins (polypeptides); the rest is non-coding.
• Information flows in the cell from DNA to messenger RNA (mRNA) through transcription, then to transfer RNA (tRNA), and finally to protein through translation.
• mRNA carries genetic instructions from DNA to ribosomes.
• tRNA brings amino acids to ribosomes for protein synthesis.
• During translation, mRNA carries the DNA code to the ribosome, tRNAs (with a three-nucleotide sequence) bond to a unique amino acid, and the DNA code is transferred to make a specific protein.

Genes, Alleles, Genotype, and Phenotype

• Genes are nucleotide sequences coding for a protein at a specific location on a chromosome.
• Alleles are different versions of a gene (dominant or recessive).
• Genotype is the genetic makeup (e.g., AA, Aa).
• Phenotype is the observable trait (e.g., eye color).
• AA is homozygous dominant, Aa is heterozygous, aa is homozygous recessive.
• A human can have one or two types of alleles for a gene, but single genes do not create phenotypes.
• Two copies of a recessive gene are needed to express a genetic disease (aa).

Mutations

• Fathers pass on four times more mutations for childhood diseases than mothers because women are born with a finite number of eggs, while men produce new sperm throughout life via spermatogenesis.
• As men age, sperm precursor cells undergo more divisions, increasing the opportunity for new mutations to arise.

Simple Genes

• An example of a simple gene trait that is dominant only requires a single copy of the allele to express (e.g., Huntington's disease).
• An example of a simple gene trait that is recessive requires both alleles to be present for the trait to occur (e.g., cystic fibrosis).

Antigens

• Antigens are molecules (proteins, carbohydrates, or lipids) on the surface of cells that trigger an immune response.
• Blood types (A, B, AB, O) are determined by the presence or absence of antigens on red blood cells.
• The Rh factor (+ or -) is an antigenic protein on red blood cells that can cause complications during pregnancy or transfusions.

Hemolytic Disease of the Fetus

• Hemolytic disease of the fetus (HDF) happens when the mother's immune system attacks the fetus' red blood cells due to antigen incompatibility, usually related to the Rh factor.
• Rh- mothers carrying Rh+ fetuses can develop antibodies during the first pregnancy, which can then cross the placenta in subsequent pregnancies and destroy fetal red blood cells.
• HDF can be prevented by injecting the mother with a drug to prevent her antibodies from reacting to the baby's antigens.

Phenylketonuria

• Phenylketonuria (PKU) is a genetic disorder caused by a mutation in the PAH gene, which encodes the enzyme phenylalanine hydroxylase.
• PKU follows an autosomal recessive pattern, requires two defective copies of the gene, and leads to intellectual disorders.

Single Gene with 3+ Types

• Some single gene traits have more than two alleles, though each individual inherits only two
• An example includes the ABO blood system where AA and AO both result in a Type A outcome, BB and BO both result in a type B outcome, and OO results in Type O.

Polygenic Traits

• Polygenic traits are influenced by multiple genes (polygenes).
• Polygenic traits show a continuous range of phenotypes (e.g., height, skin color).
• Polygenic traits often follow a normal distribution in a population.
• Polygenic traits are influenced by both genetic and environmental factors.
• Height is controlled by hundreds of genes, each contributing incrementally, while nutrition plays a significant environmental role.
• Skin color is determined by multiple genes affecting the type and amount of melanin produced and environmental exposure to sunlight.

Traits Comparison

• Simple traits are influenced by 1 gene and polygenic traits are influenced by multiple genes.
• Simple traits have distinct phenotypic categories (e.g., tall/short, A/O blood type), whereas polygenic traits are continuous (e.g., varying heights).
• The inheritance pattern of simple traits is predictable, while the inheritance pattern of polygenic traits in less predictable.
• The environmental influence on simple traits is minimal, whereas there is significant environmental influence on polygenic traits.

Epigenetic Effects

• Epigenetic effects are changes in gene expression or phenotype without altering the DNA sequence.
• These effects can be caused by normal development, trauma, chemicals, drugs, aging, and diet.
• Epigenetic markers can last a lifetime but are typically erased during gamete production, although some are passed on and affect the prevalence of some diseases and cancers.

Sources of Genetic Variation

• Genetic variation is essential for evolution and the survival of species.
• Mutations are permanent changes in the DNA sequence that can create new alleles (e.g., single nucleotide errors during replication).
• Siblings don’t look identical because of sexual recombination and independent assortment of chromosomes during meiosis.

Meiosis

• During meiosis, a specialized cell division produces haploid gametes (sperm and egg cells) from diploid germ cells.
• 2^23 genetically different gametes can be made due to sexual recombination.

Race

• Races exhibit differences in morphology or genetics.
• Race is a social construct with little biological basis.
• Humans share about 99.9% of their DNA, implying minimal genetic differences between populations.

Skin

• Skin is the largest organ.
• Skin weighs approximately 10 - 15 lbs and has two layers: the epidermis (contains dead skin cells and pigmentation) and the dermis (houses blood vessels, nerves, and glands).
• Skin functions to protect, thermoregulate, and provide sensory perception.

Biology of Skin Color

• Melanin is the main pigment responsible for skin, hair, and eye color.
• Melanin protects against UV radiation, preventing DNA damage and folate degradation, making it a natural a natural sunscreen.

Evolution of Skin Color

• Early humans in Africa developed dark skin to shield against intense UV radiation.
• As humans migrated to regions with less sunlight, lighter skin evolved to facilitate vitamin D production.

Charles Darwin's View on Race

• Monogenic Perspective is Charles Darwin's belief that all humans belonged to the same species.
• Cultural Imperialism perspective is Charles Darwin's thought that European civilization was superior to indigenous cultures.
• Charles Darwin suggested that civilized races would eventually replace savage races, reflecting the era’s colonial mindset.

Human Evolution Timeline

• 6 million years ago: The last common ancestor of chimpanzees and humans existed.
• 1.9 million years ago: Homo erectus emerged in Africa and migrated to Eurasia.
• 600,000 years ago: Two evolutionary lines split, with Neanderthals in Europe, Denisovans in Asia, and Homo sapiens sapiens in Africa.

Multi-Regionalism Hypothesis

• The multi-regionalism hypothesis suggests that Homo erectus populations across different continents evolved into modern humans independently.
• This would mean human "races" diverged 1.7 million years ago.
• The multi-regionalism hypothesis has been debunked due to strong genetic evidence against it.

Genetics of Race

• The Human Genome Project found that all humans are more than 99% genetically identical.
• Richard Lewontin found that 85.4% of genetic variation is within populations, 8.3% is between populations within a race, and only 6.3% is between races.

Evolution of Skin Color and Adaptations

• Skin color evolved independently in different populations but skin color does not define race.
• Dark skin was the ancestral trait, and lighter skin evolved rapidly in northern populations due to vitamin D needs.

Sex

• Sex (noun) is a biological classification into male and female based on reproductive anatomy and gamete production.
• Males produce small, motile gametes (sperm), and females produce large, immotile gametes (eggs).
• Sex (verb) is the process of gene mixing, combination, or transfer between individuals, not limited to fertilization.
• Sexual reproduction is the combination of genetic material from two parents, which creates genetically diverse offspring.
• Asexual reproduction is clonal reproduction without gamete fusion.

Eukaryotic Reproduction

• All eukaryotes engage in sexual reproduction at some point in their life cycle.
• Animals primarily reproduce sexually while certain animals also exhibit asexual reproduction.
• Plants alternate their generations and some are dioecious (separate sexes) and others are hermaphroditic.
• Fungi have unique mating types. Fungi lack defined biological sexes but engage in sexual reproduction.

Asexual Reproduction

• During asexual reproduction, binary fission makes an exact copy (except for mutation).
• In asexual reproduction, no combining, mixing, or transferring of genes is involved.

Sequential Hermaphroditism

• Sequential hermaphroditism is not found in mammal or bird species.
• Protandry: Born male-to-female transition (e.g., clownfish)
• Protogyny: Born female-to-male transition (e.g., wrasses, groupers)

Males and Sex Determination

• Males evolved primarily to increase genetic diversity through gamete production.
• Some species exhibit male parasitism (e.g., anglerfish, where males fuse to females for reproduction).
• Chromosomal Sex Determination in Mammals consists of XX (female) and XY (male).
• Chromosomal Sex Determination in Birds consists of ZW (female) and ZZ (male).

Mating Systems in Animals

• Monogamy: One Mating Per Breeding Season (e.g., swans).
• Polygyny: One Male Mates with Multiple Females (e.g., lions, gorillas).
• Polyandry: One Female Mates with Multiple Males (e.g., seahorses).

Reproductive Traits

• Duration of parental care = Extended (18+ years for humans) vs. Shorter duration for apes
• Ovulation = Concealed for humans vs. Opened (e.g. swelling in chimpanzees) for Apes
• Sexual Receptivity = Constant for humans vs. Cyclical for apes
• Mating System = Mostly monogamous for humans vs. More polygamous for apes
• Sexual Dimorphism = Small for humans vs. Larger (gorillas) for apes
• Penis Size = Large relative to body for humans vs. Smaller for apes
• Breast Size = Permanently enlarged vs. Swell during lactation only

Genotypic Sex

• XX = Female (99% of biological females have this genotype).
• XY = Male (99% of biological males have this genotype).

Key Processes in Sex Determination

• Early Development (~6 Weeks): Embryo has primordial gonads, Wolffian Ducts develop into male structures, and Müllerian Ducts develop into female structures.
• Gene Activation (~7 Weeks): Sry Gene on Y Chromosome Triggers testes development and Testes produce testosterone, thus suppressing female development.
• Sex Hormones Drive Differentiation: Testosterone leads to male genitalia, and the absence of the Sry gene causes ovaries to develop.
• Puberty Completes Sexual Maturation with a surge in sex hormones which leads to secondary sexual characteristics.

Sex Hormones & Effects

• Testosterone is produced by testes to develop male sex organs and create muscle growth.
• Estrogen is produced by the ovaries, creating the female productive system and secondary sex traits.
• Progesterone is also produced by the ovaries to regulate the menstrual cycle and maintain pregnancy.