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• Genetics is the biology branch studying heredity and organismal variation.

Genetics: Key Concepts

• The answer to why people inherit certain traits lies within the cell.

Chromosomes

• Chromosomes carry hereditary information (genes).
• They consist of nucleotides arranged in DNA.

DNA, RNA, and Proteins

• DNA is transcribed into RNA, which is then translated into proteins.

Nucleus

• The nucleus is a crucial cell part containing chromosomes.
• It's enclosed by a membrane.

Chromosomes

• Each cell contains 23 chromosome pairs.
• They become visible during cell division.

DNA (Deoxyribonucleic Acid)

• The genetic material composed of nucleotide polymers (polynucleotides).
• Polymers consist of repeating simple units.

The DNA Structure

• The double helix of DNA was discovered in 1953.
• It revealed how genetic information is stored.
• The discovery of DNA's structure revolutionized biology and genetics, enhancing the understanding of inheritance and evolution
• DNA has a twisted ladder appearance.
• It consists of two strands with nitrogenous bases.
• These bases are Adenine (A), Cytosine (C), Guanine (G), and Thymine (T).
• A pairs with T, and C pairs with G in the helix.

Nucleotides

• Form the basic units of DNA
• Composed of a phosphate group, deoxyribose, and nitrogenous base (A, C, G, or T).

The Human Genome

• It utilizes only four "letters."
• Purines are adenine and guanine.
• Pyrimidines are thymine and cytosine.

Purines

• Heterocyclic aromatic organic compounds with a pyrimidine ring fused to imidazole ring.
• They feature a double-ring structure.
• Adenine (A) and guanine (G) are examples of purines.
• Found in both DNA and RNA.
• It pairs with pyrimidines via hydrogen bonds.
• This maintains DNA and RNA stability.
• Adenine pairs with thymine (DNA) via two hydrogen bonds.
• Guanine pairs with cytosine via three hydrogen bonds.

Pyrimidines

• Pyrimidine is similar to benzene and has a single-ring structure.
• Examples include cytosine (C), thymine (T), and uracil (U).
• Cytosine- found in both DNA and RNA
• Thymine - DNA only
• Uracil - RNA only
• Pyrimidines pair with purines for accurate base pairing.
• Cytosine pairs with guanine.
• Thymine (or uracil) pairs with adenine.

DNA Functions

• It stores genetic information for organism characteristics.
• It replicates accurately for cell division and growth.
• Transcription and translation- DNA is transcribed into RNA, then translated into proteins.
• It's inherited, passing traits from parents to offspring.

DNA Replication

• DNA replication duplicates the molecule before cell division.
• The strands separate, and new complementary strands are built.
• DNA replication is essential for cell reproduction and inheritance.

Steps of DNA Replication

• Strand separation: DNA strands unwind, breaking hydrogen bonds.
• Complementation: Nucleotides pair with exposed bases on each strand.
• New strand formation: Paired nucleotides form new strands.
• Two DNA molecules: Results in two identical DNA molecules for cell division.

Importance of Accuracy

• DNA replication ensures accurate genetic copies during cell division.
• Without it, genetic errors and cellular dysfunctions can occur.

DNA, Genes, and Chromosomes

• DNA forms genes
• Multiple genes group into chromosomes.
• Chromosomes are located within the nucleus
• They contain all the genetic information.

Genes and Chromosomes:

• Genes are DNA segments with protein synthesis instructions.
• Chromosomes are structures of DNA and protein housing genes in the nucleus.

Alleles:

• Alleles are versions of a gene.
• Individuals inherit two alleles per gene, one from each parent.
• Alleles are located in homologous chromosomes.

Alleles: Homozygous vs. Heterozygous

• Homozygous: Identical alleles yield a homozygous individual for that gene (e.g., PP).
• Heterozygous: Different alleles yield a heterozygous individual (e.g., Pp).

Genetic Vocabulary

• Gene and allele are key terms.
• Dominant and recessive alleles influence expression.
• Genotype is the genetic makeup.
• Phenotype is the physical expression.
• Homozygous and heterozygous refer to allele pairings.
• Hybrid refers to mixed traits.
• Monohybrid and dihybrid describe genetic crosses.
• Generations are labeled F1, F2, etc.
• Reciprocal cross, backcross, and test cross are experimental techniques.

William Bateson:

• Founder of genetics, popularized Mendel's ideas after rediscovery.
• Genetic linkage co-discoverer, coined "epistasis" for gene interaction.

Genotype and Phenotype:

• Genotype: Genetic makeup.
• Phenotype: Physical appearance.

Genotype and Phenotype Expression:

• Phenotype is the expression of genotype.
• Influenced by genotype and environment.
• Trait example: height.
• Phenotype: tall or dwarf.
• Genotype: TT, Tt, or tt.
• Heterozygous: Inherited different gene forms.
• Homozygous: Chromosome copies have identical sequences.
• Hemizygous: Only one gene copy present diploid cells.

Heterozygous vs Homozygous Example:

• Tallness (TT or Tt), dwarfism (tt).
• Hemizygous: X chromosome genes in males

Hybridization

• The process of producing hybrid offspring by mating different varieties.
• Liger: A lion-tiger hybrid
• Hybrid offspring: exhibit differing traits.
• Monohybrid: cross differing by single gene.
• Dihybrid: experiment crossing two traits.

Monohybrid and Dihybrid Crosses

• Monohybrid: cross individual organisms differing by one allele pair under study.
• Dihybrid: cross between individual organisms differing by two allele pairs.
• Filial generation (F) is offspring.
• F1 is the first cross between distinct plants
• F2 is the cross's next generation.

Genetics: Reciprocal Cross

• Reciprocal cross assesses parental sex role on inheritance pattern.
• Parental sex roles can play a crucial aspect in hereditary traits
• All parent organisms must be true breeding.

Genetics: Backcross Technique

• The Backcross technique crosses a hybrid with parent.
• It recovers genetic identity closer to parent.
• It is used in horticulture, breeding, and gene knockouts.
• Tall (Tt) pea plant crossed with pure tall (TT) or dwarf (tt).

The Genetics Test Cross Method

• Test cross determines unknown genotype individuals
• It uses homozygous recessive organism.
• It also assesses dominant phenotype.
• Example: purple flower (PP or Pp) tested with white flower (pp).
• By assessing the genotype based on offspring

What are Genes?

• In humans, they vary from hundreds to millions of DNA bases
• Genes are composed of segments of DNA, the molecule that encodes genetic information in cells
• They instruct and regulates the production of molecules.
• Some genes don't encode protein.
• A gene is the basic unit of heredity.

Terminologies: Gene

• Determines offspring characteristics.
• "Gene" term coined in 1909 by Wilhelm Johannsen.
• Consist of continuous segment of DNA.
• Eukaryotes occupies the specific position on the chromosomes called locus (loci).

Gregor Johann Mendel: Historic Background

• Austrian monk born in Czech Republic, 1822.
• Studied theology, botany, scientific method.
• Worked eight years with pure pea lines.
• Prior to Mendel, heredity was "blending".
• Mendel's work (1856-1864) on Pisum sativum led to modern genetics concepts.

Gregor Johann Mendel Contributions

• In 1866 publication established Inheritance Principles.
• He couldn't replicate work in asexual plants.
• Mendel's work rediscovered in 1900 after 34 years.
• His work: Genes come in pairs and is inherited as distinct units
• He tracked gene segregation and their appearance in offspring.
• He recognized the mathematical patterns of inheritance

Rediscovery of Gregor Johann Mendel Findings

• In 1900 rediscovered independently by 3 botanist
• Carl Corens (Germany), Hugo deVries (Holland), Erich von Tsechermak (Austria).

The Seven Traits or Characteristics Mendel Assessed

• Pea's were shape, color, pod's color, shape, and stem length

Mendelian Inheritance Principles:

• It opposes believes of attributes blending
• Instead, heredity is based on discrete inheritance units
• The units being called genes afterward

The Gene Theory of Inheritance

• Gregor Mendel discovered the basic laws of heredity

Why did Mendel choose to study pea plants?

• Multiple variable traits that can clearly be seen
• Short Generations with offspring are many
• Mating easy- Pea plant can be controlled

Hybridization

• This is the process that create hybrid by mating different varieties or special

The Terminology of Generations

• True-breeding
• F1 Generation (first filial)
• F2 generation (second filial)

Geneticists Mendel's Laws

• The Law of Dominance
• The Law of Segregation
• The Law of Independent Assortment

The Law of Segregation

• Each trait we inherit, eye color or hair type, is controlled by two versions of a gene.
• During reproduction, are randomly split so that the egg or sperm gets only one version (not both).
• The baby ends up with one version of the gene from each parent - creating the pair

The Law of Independent Assortment

• The Law of Independent Assortment means that genes controlling different traits, like eye color and height, are passed down independently of each other. •
• Traits are passed down independently of each other
• Every trait is controlled by a gene
• Organisms have two versions of each gene
• Genotype nucleotide sequence
• Phenotype visibly expressed trait
• Geneticist has described genes without the knowledge of the DNA
• True-breeding plants have two identical alleles

The Law of Dominance-

• The Law of Dominance- An organism with alternate forms of a gene will express the form that is dominant.
• Gametes have only one allele
• The offspring have two alleles (one from each parent)

Additional Concepts

• Certain alleles are not completely dominant or recessive
• Multiple alleles
• Single gene can produce multiple phenotypes

Genetic Traits

• Include straight thumb, detached earlobes etc
• Huntington’s disease results from HTT gene mutation on chromosome 4
• The mutation involves excessive CAG repeats.
• This causes symptoms which typically begin between the ages of 30 and 50

Huntington's Disease Symptoms

• Symptoms worsen and come in 3 categories:
• Motor = involuntary movements.
• Cognitive = difficulty concentrating, memory loss
• Psychiatric = Depression, anxiety, and psychosis
• Inheritance is autosomal dominant.
• Genetic testing can confirm CAG repeat expansion in the HTT gene.

Managing Huntington's Disease

• There is currently no cure for the illness
• This includes with medications, psychiatric and counseling treatments

Huntington's Disease Prognosis

• The disease is progressive, meaning symptoms worsen over time
• Life expectancy usually between 15–20 years.

Tay-Sachs Disease (Recessive Inheritance)

• Caused by a mutation in the HEXA gene on chromosome 15
• Leads to deficiency of beta-hexosaminidase A beta enzyme
• Results in excessive GM2 ganglioside accumulation
• It is autosomal recessive
• Diagnosed through enzyme and by identifying the carrier genes

Diagnosing and Treating Tay-Sachs

• Testing of the enzyme
• Testing for the presence of carrier genes
• Treatment relies on managing symptoms and supportive care.
• There is no cure currently

Albinism

• Is a rare genetic disorder
• Characterized by a lack of melanin.
• Caused by mutations in genes
• It affects all skin and hair
• All ethnic groups
• Effects both males and females

Types of Albinism

• Albinism is either Oculocutaneous Albinism (OCA) or Ocular Albinism
• Primarily affects their eyes
• Often inherited in an X-linked recessive manner
• Occurs mostly in males

Oculocutaneous Albinism (OCA):

• Affects the skin, hair,
• Inherited in an autosomal recessive pattern.
• Must inherit two copies of the mutated gene (one from each parent) to express the disease
• Can vary from white to blonde
• This also results in increase risks of skin cancer

Phenylketonuria, Recessive Inheritance:

Is caused by mutations in the PAH gene

• This results in the body building up to toxic levels

Neuro & Cognitive

• The illness can result in mental disability if left untreated
• Physical - Fair skin and hair

Diagnosis

• Testing of the enzyme
• Testing for the presence of carrier genes
• Treatment relies on managing symptoms and supportive care.
• There is no cure currently

Non-Mendelian inheritance

• Genetic patterns that do not follow Mendel's laws of dominant and recessive traits.
• It focuses on traits that Influenced by environment, gene interactions etc
• Incomplete dominance, results in one parent not over powering the other. Rather they are combined

Dominance in Human traits

• The genes controlling the trait (hair) do not over power each other they both co exist

Incomplete Dominance

• Individuals with one allele for straight hair and one for curly hair tend to have wavy hair, which is a mix of both textures.
• When individuals with very light skin and very dark skin have children, their offspring often have an intermediate skin tone

Conclusion

• Codominance plays an important role in genetic diversity, -
• This can be a strong aspect in blood type compatibility, While not as common many species can rely multiple characteristics

Multiple Traits

• The presence a gene has more than 2 possible
• Can be ABO group

Multiple Alleles in Human Inheritance

• The more alleles present increase genetic diversity in a population They do not always indicate the disease , but rather a combination of 2 genes to influence the expression to be a mix of the 2 genes.