Albinism: Hopi Tribe and Genetics

Albinism in the Hopis

• Black Mesa in northeastern Arizona is the ancestral home of the Hopi Native Americans
• Oraibi, a Hopi village on Black Mesa, has existed since 1150 C.E. and is North America's oldest continuously occupied settlement
• In 1900, Aleš Hrdlička found 11 white Hopi Native Americans, with a genetic condition known as albinism

Albinism

• Albinism is due to a defect in enzymes required for melanin production, affecting skin, hair, and eyes
• People with albinism produce little to no melanin, resulting in white hair, light skin, and lack of iris pigment
• Melanin protects skin cell DNA from UV radiation and is essential for eyesight development
• Archibald Garrod described albinism's genetic basis in 1908 as an autosomal recessive trait
• Albinism requires two copies of an albino mutation, one from each parent
• Albinism can result from mutations in genes controlling melanin synthesis and storage
• Oculocutaneous albinism type 2, is common among Hopis, caused by a defect in the OCA2 gene on chromosome 15
• Albinism is present in almost all human ethnic groups, but the Hopis have a high frequency of it
• Albinism frequency in most human groups: 1 in 20,000 individuals
• Albinism frequency on Black Mesa: 1 in 200, a hundred times higher than other populations
• Geneticists speculate that the high albinism frequency relates to its special place in Hopi culture
• Historically, Hopis considered those with albinism important and a sign of pure Hopi blood
• Individuals with albinism performed Hopi ceremonies and held leadership positions
• Hopis with albinism received special treatment and were excused from farming due to increased risk of sunburn and poor eyesight
• Men with albinism may have had a mating advantage because they stayed in the village

Genetics

• Genetics studies heredity, inherited variation encoding, replication, expression, and evolution
• Genetics includes transmission, molecular, and population genetics
• Genetics is a rapidly advancing science with new discoveries reported frequently
• Genetics has significant economic and ethical implications
• The chapter introduces genetics and reviews concepts

Genetics: Importance to Individuals, Society, and Biology

• Genes significantly influence lives, affecting height, weight, hair color, and disease susceptibility
• Genes contribute to intelligence, personality, and are fundamental to who we are
• Genetics aims to separate genetic and environmental influences on individual variation.
• Agriculture began applying genetic principles to plant and animal domestication
• Extensive genetic alteration has improved modern crops and animals through disease, pest resistance and nutritional qualities
• The Green Revolution expanded food production using genetic methods
• Genetically engineered crops include corn, soybeans, canola, squash, and sugar beets
• The pharmaceutical industry uses genetically manipulated fungi and bacteria
• The biotechnology industry uses molecular genetic techniques for mass production
• Mass produced products include antimalarial drugs, growth hormone, insulin, clotting factor, antiviral drugs, enzymes, antibiotics, and vaccines
• Genetics generates bacterial strains to remove minerals, break down toxic chemicals, and produce biofuels
• Genetics plays a critical role in medicine
• Hereditary components are recognized in rare genetic disorders like sickle-cell anemia and Huntington disease, as well as common diseases such as asthma, diabetes, and hypertension
• Advances in genetics include diagnostic tests and identification of disease-causing mutations.
• Genomic data facilitates personalized medicine
• Rapid sequencing methods allow for complete genome sequence information to assess disease susceptibilities
• Gene therapy, direct gene alteration, is used to treat diseases but remains experimental and limited
• Genetics is crucial for biology students as it provides unifying principles
• Genetics underlies various biological disciplines like evolution and developmental biology
• Taxonomy, ecology, and animal behavior increasingly use genetic methods
• Studying any field of biology or medicine requires a thorough understanding of genes and genetic methods

Genetic Diversity and Evolution

• Life on Earth has an array of forms and features, adapted to almost every environment.
• Life's history involves emerging, disappearing, and changing forms.
• Organisms use similar genetic systems with a genome encoded in either DNA or RNA.
• Genetic instructions are in the same format, processes are similar
• These common features suggest that Earth life evolved from a primordial ancestor 3.5 to 4 billion years ago
• Biologist Richard Dawkins describes life as a river of DNA connecting all organisms.
• Study of one organism's genes reveals principles applying to others
• Investigating bacterial DNA replication informs human DNA replication
• Genes from one organism can function in foreign cells, enabling genetic engineering
• Similar genetic systems are the basis for diseases like AIDS, where viral genes function in human cells.
• Life's diversity and adaptations are products of evolution (genetic change over time)
• Evolution is first, differences arise randomly, and second proportions change over time
• Genetic variation is the base of evolutionary change and life
• Molecular genetics deciphers evolutionary relationships (example: Neanderthal DNA)
• Understanding genetics and genetic variation is vital for the past, present, and future of life

DNA in the Biosphere

• DNA molecules are small, but because all cells contain genetic information, there is a tremendous amount of DNA in the world
• The total amount of DNA in the biosphere is 5.3 × 1031 megabase pairs
• The DNA weighs approximately 50 billion tons
• Storing that much information would require 10^21 computers
• Scientists catalog and measure biodiversity through DNA analysis
• The Earth BioGenome Project (EBP) proposes sequencing the genomes of 1.5 million known eukaryotic species

Divisions of Genetics

• Genetics consists of three subdisciplines: transmission, molecular, and population genetics
• Transmission genetics (classical genetics) studies heredity and how traits pass between generations
• Transmission genetics deals with chromosomes, heredity, gene arrangement, and gene mapping
• Focuses on individual organism, inheritance, and gene passing
• Molecular genetics studies the gene's chemical nature, genetic information encoding, replication, and expression
• Molecular genetics includes replication, transcription, translation, and gene regulation
• Focuses on the gene structure, organization, and function
• Population genetics explores genetic composition of populations and its changes geographically and over time
• Population genetics studies evolution and the group of genes in a population
• Divisions are convenient but overlapping and can be further specialized
• Can be subdivided by organism and studied at different levels

Model Genetic Organisms

• Model genetic organisms are widely used in genetic research and serve as models for other organisms
• They have characteristics useful for genetic analysis and accumulated genetic information
• Six model organisms include:
  • Drosophila melanogaster (fruit fly)
  • Escherichia coli (bacterium)
  • Caenorhabditis elegans (nematode)
  • Arabidopsis thaliana (thale-cress plant)
  • Mus musculus (house mouse)
  • Saccharomyces cerevisiae (baker's yeast)
• Share life cycles and traits suitable for genetic study:
  • Short generation time
  • Manageable numbers of offspring
  • Adaptability to laboratory environment
  • Inexpensive housing and propagation
• Other species considered genetic models:
  • Neurospora crassa, Zea mays, Danio rerio, Xenopus laevis
• Homo sapiens is also studied intensively
• Zebrafish have helped identify genes affecting pigmentation
• The zebrafish is a small vertebrate, produces many offspring and is easy to rear
• Zebrafish mutant "golden" has light pigmentation and fewer melanosomes
• SLC24A5 gene in the zebrafish, affects calcium uptake
• The homologue in humans affects skin pigmentation, accounting for a percentage of the differences between Africans and Europeans

Early use and Understanding of Heredity

• Humans have been using genetic principles for thousands of years
• Domestication of plants and animals occurred approximately 10,000 to 12,000 years ago
• First crops included wheat, peas, lentils, and barley. and animals such as dogs, goats and sheep
• By 4000 years ago selective breeding was in use
• Assyrians and Babylonians developed varieties of date palms
• Ancient writings show awareness of heredity, for example Hindu sacred writings
• The Talmud shows an understanding of hemophilia inheritance
• Greek philosophers created pangenesis, where genetic information comes from each body part
• Specific particles, gemmules, carry information to reproductive organs for embryo
• Traits acquired in a person's life become incorporated into that person's hereditary information and are passed on to offspring
• The ancient Romans developed animal and plant breeding techniques
• Robert Hooke discovered cells
• Preformationism (inside the egg or sperm there exists a fully formed miniature adult, a homunculus, which simply enlarges in the course of development).
• Blending inheritance suggests that traits in offspring are a mix, such as with pigments

Science of Genetics

• Nehemiah Grew reported in 1676, that plants reproduce sexually
• Gregor Mendel discovered basic heredity principles
• Developments in nineteenth century cytology influenced genetics
• Robert Brown described the cell nucleus
• Matthias Jacob Schleiden and Theodor Schwann developed "cell theory"
• Walther Flemming observed chromosome division and described mitosis
• Biologists recognized the cell nucleus contains hereditary information
• Charles Darwin put forth the theory of evolution by natural selection
• Darwin recognized heredity's importance but did not understand inheritance
• Cytologists demonstrated the nucleus's role in fertilization
• August Weismann disproved inheritance of acquired characteristics and proposed germ-plasm theory
• 1900, year genetics was established by Gregor Mendel
• In 1902, Walter Sutton proposed that genes are located on chromosomes
• Thomas Hunt Morgan discovered the first mutant fruit fly
• Ronald A. Fisher, John B. S. Haldane, and Sewall Wright integrate genetics and evolutionary theory
• Bacterial and viral use in genetics began
• DNA recognized as repository of genetic information
• James Watson, Francis Crick, Rosalind Franklin, and Maurice Wilkins described the DNA structure
• The chemical structure of DNA studied worked out. Genetic material recombined in experiments
• Walter Gilbert and Frederick Sanger developed DNA sequencing methods
• Kary Mullis developed PCR process
• Gene therapy was introduced in 1990
• Haemophilus influenzae used in a bacterial sequence
• Eukaryotic organism sequence first released
• Jennifer Doudna and Emmanuelle Charpentier modify the CRISPR-Cas systems

Cutting Edge of Genetics

• DNA sequencing increased and rapid methods in use for DNA
• DNA sequencing can sequence single molecules
• Genes responsible for loss of flavor in tomatoes identified in research through flavor enhancing
• Blood tests have been developed providing detection of DNA from tumors, increasing potential for early detection of cancer
• Genetics information used to combat infectious diseases, creating vaccines from viruses like HIV, Zika and Ebola
• Human gene therapy has been harnessed to diseases ranging from Leukemia, to cancer
• Researchers have identified genes which allow traditional divers in Southeast Asia to stay underwater for longer periods of time
• Focus shifting from species to species differences
• Sequencing can asses risk of aquiring an individual future