Honors Bio Final Exam

Chapter 8: DNA Structure and Function / Karyotypes

Key Terms and Definitions

• Bacteriophage: A virus that infects bacteria, used in molecular biology to understand DNA.

• Autosome: Any chromosome that is not a sex chromosome; humans have 22 pairs of autosomes.

• Karyotype: A visual representation of an individual's chromosomes, used to identify chromosomal abnormalities.

• Trisomy: A genetic condition where an individual has three copies of a chromosome instead of two, e.g., Down syndrome (Trisomy 21).

• Monosomy: A genetic condition where an individual has only one copy of a chromosome instead of two, e.g., Turner syndrome (Monosomy X).

• Nucleosome: The basic unit of DNA packaging, consisting of a segment of DNA wound around a core of histone proteins.

Key Research Studies

• Fredrick Griffith’s Research: Demonstrated the process of transformation in bacteria, concluding that a 'transforming principle' (DNA) could transfer genetic information.

• Hershey and Chase Experiment: Used bacteriophages to show that DNA, not protein, is the genetic material, confirming DNA's role in heredity.

• Typical Virus Structure: Composed of genetic material (DNA or RNA) surrounded by a protein coat (capsid), sometimes with a lipid envelope.

DNA Structure and Function

• Structure of a DNA Nucleotide: Composed of a phosphate group, a deoxyribose sugar, and a nitrogenous base (A, T, C, G).

• Base Pairing: Adenine pairs with Thymine (A-T) and Cytosine pairs with Guanine (C-G) through hydrogen bonds, forming the rungs of the DNA ladder.

• DNA Backbone: Made of alternating sugar and phosphate molecules, providing structural stability.

Karyotypes and Genetic Disorders

• Reading a Karyotype: Can determine the sex of an individual (XX female, XY male) and identify chromosomal abnormalities such as trisomy or monosomy.

• Differences Between Autosomes and Sex Chromosomes: Autosomes are non-sex chromosomes, while sex chromosomes determine an individual's sex (X and Y).

• Common Genetic Disorders: Examples include Down syndrome (Trisomy 21), Turner syndrome (Monosomy X), and Klinefelter syndrome (XXY).

Chapter 9: DNA, RNA, and Protein Synthesis

Transcription and Translation

• Transcription Process: The synthesis of mRNA from a DNA template, occurring in the nucleus, involving RNA polymerase and the formation of a 5' cap and poly-A tail.

• Translation Process: The decoding of mRNA into a polypeptide chain at the ribosome, involving tRNA and ribosomal RNA (rRNA).

• Codons and Anticodons: Codons are three-nucleotide sequences on mRNA that specify amino acids, while anticodons are complementary three-nucleotide sequences on tRNA.

Genetic Code and Mutations

• Genetic Code: The set of rules by which information encoded in mRNA is translated into proteins, with 64 codons coding for 20 amino acids.

• Types of Mutations: Include substitution (one base replaced), insertion (extra base added), and deletion (base removed), each affecting protein synthesis differently.

• Importance of Proteins: Proteins perform essential functions in the body, including enzymes, structural components, and signaling molecules.

Differences Between DNA and RNA

• DNA vs RNA: DNA is double-stranded, contains deoxyribose sugar, and uses thymine; RNA is single-stranded, contains ribose sugar, and uses uracil instead of thymine.

• Introns and Exons: Introns are non-coding regions removed during mRNA processing, while exons are coding regions that remain and are expressed in proteins.

Chapter 12: Meiosis

Phases of Meiosis

• Meiosis Overview: A two-stage process of cell division that reduces the chromosome number by half, producing four haploid gametes from one diploid germ cell.

• Phases of Meiosis: Includes Meiosis I (homologous chromosomes separate) and Meiosis II (sister chromatids separate), each with distinct stages (prophase, metaphase, anaphase, telophase).

• Crossing Over: Occurs during prophase I, allowing exchange of genetic material between homologous chromosomes, increasing genetic diversity.

Genetic Variation in Meiosis

• Tetrad Formation: Tetrads form during prophase I when homologous chromosomes pair up, allowing for crossing over.

• Importance of Genetic Variety: Crossing over and independent assortment during meiosis contribute to genetic diversity, essential for evolution and adaptation.

Chapter 13: Genetics and Inheritance

Mendelian Genetics

• Dominant and Recessive Traits: Mendel's experiments showed that dominant traits mask recessive traits in offspring, determining phenotype based on genotype.

• Genotype vs Phenotype: Genotype refers to the genetic makeup (homozygous or heterozygous), while phenotype is the observable trait.

• Punnett Squares: A tool used to predict the probability of offspring genotypes and phenotypes based on parental alleles.

Genetic Variation and Inheritance Patterns

• Segregation and Independent Assortment: Segregation ensures that alleles separate during gamete formation, while independent assortment allows for the random distribution of different genes.

• Importance of Genetic Variety: Genetic diversity is crucial for species survival, allowing populations to adapt to changing environments.

Types of Inheritance

• Codominance and Incomplete Dominance: Codominance occurs when both alleles are expressed equally (e.g., AB blood type), while incomplete dominance results in a blended phenotype (e.g., red and white flowers producing pink).

• Polygenic Inheritance: Traits controlled by multiple genes, leading to a range of phenotypes (e.g., skin color, height).

Chapter 14: Pedigrees and Genetic Disorders

Understanding Pedigrees

• Definition of a Pedigree: A diagram that shows the occurrence of a genetic trait across generations, useful for tracking inheritance patterns.

• Carriers and Traits: Carriers are individuals who have one copy of a recessive allele, shown as half-filled circles or squares in pedigrees; affected individuals are fully filled.

• Types of Traits: Can be autosomal dominant, autosomal recessive, or sex-linked, each with distinct inheritance patterns.

Genetic Disorders and Abnormalities

• Examples of Genetic Disorders: Include cystic fibrosis (autosomal recessive), Huntington's disease (autosomal dominant), and hemophilia (sex-linked).

• Single Gene Traits: Traits controlled by a single gene, often leading to clear inheritance patterns in pedigrees.

• Genetic Abnormalities: Variations in genes that can lead to disorders, such as chromosomal abnormalities like Down syndrome.

Genetics and Inheritance Patterns

Inheritance Patterns

• Autosomal Recessive Inheritance: This pattern requires two copies of the recessive allele for the trait to be expressed. Examples include Tay-Sachs disease and albinism.

• Tay-Sachs Disease: A genetic disorder caused by a deficiency of the enzyme hexosaminidase A, leading to the accumulation of GM2 gangliosides. Symptoms include developmental delay, loss of motor skills, and seizures.

• Albinism: A condition characterized by a lack of melanin pigment in the skin, hair, and eyes. Traits include light skin, light hair, and increased sensitivity to sunlight.

Sex-Linked Traits

• Definition: Traits that are associated with genes located on sex chromosomes, often the X chromosome.

• Inheritance in Males: Males inherit one X chromosome from their mother and one Y chromosome from their father, making them more susceptible to X-linked disorders.

• Inheritance in Females: Females inherit two X chromosomes, which can mask the effects of recessive alleles.

• Examples: Red-green color blindness, Duchenne Muscular Dystrophy, and Hemophilia are common sex-linked traits