Introduction to Genetics and Chromosomes

DNA Organization in Chromosomes

• DNA is organized into chromosomes.
• Metaphase chromosome, DNA, solenoid, chromatin fiber, nucleosomes, and histones are structural components.

Introduction to Genetics

• Genetics is important to individuals, society, and the study of biology.
• Genetics looks at transmission genetics, molecular genetics, and population genetics.

Gene for Depression Discovered

• Researchers identified P2RX7 as a gene responsible for major depressive disorders.
• Surprisingly, it has no link with serotonin.
• The gene is found in humans and animals.

Gene for Obsessive Behaviour

• Scientists discovered a gene playing a role in obsessive-compulsive disorder (OCD).
• They hope this will lead to earlier diagnosis and more effective therapies.

Genetic Variation

• Variant eye color gene discovered in Drosophila is an allele of the gene controlling eye color.
• Alleles are alternative forms of a gene that may produce observable differences, called phenotype.
• The set of alleles for a given trait is the genotype.

Dominant vs. Recessive

• A dominant allele is expressed even with a recessive allele present.
• A recessive allele is only visible when paired with another recessive allele.

Hypothetical Chromosomes

• Every gene has a specific place (locus) on a chromosome.
• Genotype is the combination of alleles in an organism.
• Phenotype is the visible expression of the genotype.
• Wild-type phenotype is the most common or generally accepted standard.
• Mutant alleles are usually recessive.

The Search for the Chemical Nature of Genes: DNA or Protein?

• Researchers sought to determine if DNA or protein held genetic information.

DNA Holds the Genetic Information

• DNA contains genetic information.

Structure of DNA

• The discovery of the double helix launched the era of molecular genetics.
• DNA is a long ladder-like macromolecule that twists to form a double helix.

The DNA: double helix

• Deoxyribonucleic acid (DNA) is the genetic material of most cells.
• DNA preserves, copies, and transmits information within cells and from generation to generation.
• The DNA's curving sides represent the sugar-phosphate backbone; the rings are the base pairs.
• DNA has antiparallel polarity and is stabilized by hydrogen bonds between bases.

Nucleic Acids

• Nucleic acids are polymers of nucleotides.
• Two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
• DNA is the genetic material storing information for replication and protein synthesis.
• RNA has various functions including protein synthesis and gene regulation.

Central Dogma

• DNA (containing instructions) is transcribed into mRNA.
• mRNA is translated into a protein.
• mRNA carries the genetic code, consisting of triplets called codons, to assemble amino acids into a protein.

Structure of DNA and RNA

• Different types of nucleic acids have different characteristics.

Structure of a Nucleotide

• A nucleotide consists of a phosphate group, a pentose sugar, and a nitrogen base.
• DNA contains adenine, guanine, cytosine, and thymine.
• RNA contains adenine, guanine, cytosine, and uracil.

Nucleotides

• Nucleotides are joined by dehydration synthesis to form a strand.

Structure of DNA and RNA

• The backbone of a nucleic acid strand is composed of alternating sugar-phosphate molecules.
• DNA consists of two strands held together by hydrogen bonds between nitrogen bases, twisting to form a double helix.
• Nucleotides may be in any order within a strand but are complementary between strands.

Large Amounts of DNA Are Packed into a Cell

• DNA is highly compacted and organized.
• Large amounts of DNA are tightly packed within a cell.

Large Amounts of DNA Are Packed into a Cell (details)

• Chromatin is a double-stranded helical structure.
• DNA is complexed with histones to form nucleosomes.
• A nucleosome consists of eight histone proteins around which DNA wraps.
• The nucleosomes fold up to produce a 30-nm fiber.
• 300nm loops are formed in DNA, then folded further to become a 250nm wide fiber, that is then tightly coiled to become a chromatid.

Characteristics of Histone Proteins

• Histone proteins are important in DNA packaging.
• Different types of histone proteins have different characteristics.

Eukaryotic Chromosome Structure

• Eukaryotic chromosomes have centromeres and telomeres.

Eukaryotic Chromosomes Possess Centromeres and Telomeres

• Centromeres are constricted regions of the chromosome.
• Telomeres are the stable ends of chromosomes.

Types of DNA Sequences in Eukaryotes

• DNA sequences are categorized as unique, moderately repetitive, or highly repetitive DNA.

Transcription

• Protein production starts in the nucleus.
• Genetic information is expressed in steps, leading to protein production.
• DNA's nucleotide sequence directs the construction of a complementary RNA sequence (mRNA).
• mRNA moves to the cytoplasm, combining with ribosomes.

Translation

• Protein synthesis is directed by information in mRNA (genetic code).
• mRNA consists of nucleotide triplets called codons.

Genetic Code

• The genetic code consists of triplet nucleotides in mRNA.
• Each triplet encodes a specific amino acid insertion in the growing protein chain.

Proteins

• Proteins have enormous structural diversity.
• Enzymes are a major category of proteins, acting as biological catalysts.

What Can Mutations Do?

• Mutations altering genes lead to altered phenotypes.
• Mutations can modify, alter, or eliminate protein function.

Functional Genomics/Transcriptomics/Proteomics

• Functional genomics studies the expression of numerous genes.
• Transcriptomics studies the transcriptome (all transcripts).
• Proteomics studies the proteome (set of expressed proteins).

Model Genetic Organisms

• Model organisms have common characteristics: short generation time, many offspring, ability for controlled crosses, easy laboratory rearing, diverse genetic variants, and substantial existing knowledge.

Model Organisms Used to Study Some Human Diseases

• Various organisms, like E. coli, S. cerevisiae, D. melanogaster, and others are used to study human diseases.

Development of Recombinant DNA Technology

• Recombinant DNA technology brought about the era of cloning.

Explore the fascinating world of genetics and how DNA is organized into chromosomes. This quiz covers crucial topics such as the structure of chromosomes, the significance of genetics in society, and recent discoveries related to genes affecting mental health and variation. Enhance your understanding of the critical role genetics plays in biology.