6.1 The Genome
3 min read•june 18, 2024
Genomes are the genetic blueprints of life. Prokaryotes have simple circular chromosomes, while eukaryotes have complex linear ones wrapped in proteins. 's structure stores genetic information using complementary base pairs.
Genetic inheritance involves chromosomes, , and traits. and sexual reproduction create genetic variation through random assortment and . Mutations introduce new alleles, further increasing diversity in populations.
Genome Structure and Organization
Structure of prokaryotic vs eukaryotic genomes
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- genomes consist of a single circular lacking a nuclear membrane with DNA located directly in the cytoplasm and contain fewer genes compared to eukaryotes (bacteria, archaea)
- May have additional small circular DNA molecules called plasmids which can be transferred between cells and confer traits like antibiotic resistance
- genomes contain multiple linear chromosomes enclosed within a nuclear membrane with DNA organized into (DNA wrapped around proteins) and possess a larger number of genes compared to prokaryotes (plants, animals, fungi)
- DNA is organized into coding regions called exons that are expressed and non-coding regions called that are spliced out during RNA processing
- Also possess separate organelle genomes in and chloroplasts which are thought to have originated from ancient prokaryotic endosymbionts ()
DNA Structure and Organization
- The consists of all the genetic material in an organism, typically stored as DNA
- DNA (deoxyribonucleic acid) is a double-stranded molecule that forms a double helix structure
- DNA is composed of nucleotides, each containing a sugar, phosphate group, and nitrogenous base
- Complementary base pairs (A-T and G-C) hold the two DNA strands together
- Genome is the process of determining the order of nucleotides in an organism's DNA
Genetic Inheritance and Variation
Chromosomes, genes, and traits in heredity
- Chromosomes are structures that carry genetic material and are composed of DNA and proteins with humans having 23 pairs of chromosomes (46 total) with each pair consisting of one maternal and one paternal chromosome
- Genes are segments of DNA located at specific positions (loci) on chromosomes that code for specific proteins or functional RNA molecules with alternative forms of a called alleles that can result in different traits (eye color, blood type)
- Traits are observable characteristics of an organism determined by the expression of one or more genes but can also be influenced by environmental factors (height, weight) and inheritance of traits follows patterns:
- - expressed when at least one dominant is present (brown eyes)
- - only expressed when two recessive alleles are present (blue eyes)
- - both alleles are expressed equally (AB blood type)
- - blending of traits (pink flowers from red and white parents)
Genetic variation from allele combinations
- Meiosis and sexual reproduction introduce genetic variation by producing gametes with a random assortment of chromosomes so independent assortment and random fertilization result in unique combinations of alleles in offspring
- Crossing over () occurs during prophase I of meiosis when homologous chromosomes exchange segments of DNA creating new combinations of alleles on chromosomes
- Mutations are changes in the DNA sequence that can occur spontaneously or be induced by mutagens (radiation, chemicals) and introduce new alleles into a population increasing genetic variation
- Point mutations include:
- Substitutions - one replaced by another
- Insertions - extra nucleotides added
- Deletions - nucleotides removed
- Chromosomal mutations include:
- Duplications - extra copies of chromosomal segments
- Deletions - missing chromosomal segments
- Inversions - reversed orientation of chromosomal segments
- Translocations - transfer of chromosomal segments between non-homologous chromosomes
- Point mutations include:
Key Terms to Review (47)
Allele: An allele is a variant form of a gene that is located at a specific position on a specific chromosome. Alleles can result in different traits being expressed in an organism, such as flower color or blood type, and contribute to genetic diversity within a population. The interaction of alleles can lead to dominant and recessive traits, playing a vital role in inheritance patterns and evolutionary processes.
Base pair: A base pair consists of two nitrogenous bases that bond together in the DNA double helix, specifically adenine (A) pairing with thymine (T) and guanine (G) pairing with cytosine (C). Base pairs are crucial for the structure of DNA, as they hold the two strands of the helix together and play a vital role in the replication and transcription processes that are essential for genetic information transfer.
Chloroplast: Chloroplasts are organelles found in plant cells and some protists that conduct photosynthesis. They convert light energy into chemical energy stored in glucose.
Chloroplast: Chloroplasts are specialized organelles found in plant cells and some algae that conduct photosynthesis, converting light energy into chemical energy stored in glucose. These organelles are crucial for life on Earth as they provide the primary source of energy for nearly all living organisms through the process of photosynthesis, linking them to various biochemical cycles and cellular functions.
Chromatin: Chromatin is a complex of DNA and proteins found in eukaryotic cells, which helps package the DNA into a more compact, organized structure. This organization is essential for efficient gene regulation, DNA replication, and repair, enabling the long strands of DNA to fit within the nucleus of a cell. Chromatin exists in two forms: euchromatin, which is less condensed and actively involved in gene expression, and heterochromatin, which is more tightly packed and typically associated with gene repression.
Chromosomal mutation: A chromosomal mutation is a change in the structure or number of chromosomes within an organism's genome, which can lead to significant genetic variation. These mutations can involve large segments of DNA and affect multiple genes, influencing traits and potentially leading to diseases. Understanding chromosomal mutations is crucial because they can play a vital role in evolution, genetic disorders, and the overall dynamics of populations.
Chromosome: A chromosome is a long, thread-like structure made of DNA and proteins that contains genetic information. It is critical in ensuring the proper segregation of genetic material during cell division, playing a key role in both inheritance and genetic variation.
Codominant: Codominance is a genetic phenomenon where two different alleles at a locus are both expressed in the phenotype of an organism. This means that neither allele is dominant or recessive, and the traits associated with both alleles are visible, often resulting in a unique phenotype. Codominance is important for understanding inheritance patterns, particularly in cases where traits do not blend but rather coexist distinctly.
Crossing over: Crossing over is a genetic process that occurs during meiosis where homologous chromosomes exchange segments of their DNA, leading to genetic variation in the resulting gametes. This exchange happens during prophase I of meiosis, and it plays a crucial role in enhancing genetic diversity, which is essential for evolution and adaptation in sexually reproducing organisms.
Deletion: Deletion refers to a type of genetic mutation where a part of the DNA sequence is lost or removed. This loss can occur in a variety of ways, such as through errors during DNA replication or from external factors like radiation. Deletions can significantly affect the structure and function of genes, potentially leading to various genetic disorders or diseases.
Deoxyribonucleic acid (DNA): Deoxyribonucleic acid (DNA) is the molecule that carries genetic information in all living organisms and many viruses. It is composed of two strands that coil around each other to form a double helix.
Diploid-dominant: Diploid-dominant refers to a life cycle in which the diploid stage is the most prominent and long-lived phase. Organisms with this life cycle, such as humans, spend most of their life cycle as diploid adults.
DNA: DNA, or deoxyribonucleic acid, is the hereditary material in almost all living organisms, encoding the genetic instructions used in growth, development, functioning, and reproduction. This molecule serves as the blueprint for all biological structures and processes, connecting various themes like the unity of life and the complexity of biological systems.
Dominant: In genetics, the term 'dominant' refers to an allele that expresses its trait over a recessive allele when both are present in a heterozygous organism. This means that if an individual carries one dominant allele and one recessive allele for a particular gene, the phenotype (observable characteristics) will reflect the dominant trait. Dominant traits can mask the effects of recessive traits, leading to important implications in inheritance patterns.
Double helix: The double helix is the structural form of DNA, consisting of two intertwined strands that resemble a twisted ladder. Each strand is composed of a backbone made of sugar and phosphate groups, with nitrogenous bases attached to the sugars forming the rungs of the ladder. This unique structure allows for the efficient storage and replication of genetic information, playing a critical role in how organisms inherit traits.
Duplication: Duplication refers to a genetic event where a segment of DNA is copied, resulting in two identical copies of that segment within the genome. This can lead to variations in gene expression and can play a crucial role in evolution by introducing genetic diversity. Duplications can occur through various mechanisms, including errors during DNA replication, and they can significantly impact an organism's traits and functions.
Endosymbiotic theory: Endosymbiotic theory proposes that certain organelles, such as mitochondria and chloroplasts, originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells. This relationship allowed these prokaryotes to become integral parts of the eukaryotic cell, leading to the complex cell structures we see today. The theory connects to the evolution of eukaryotes, emphasizing the importance of symbiotic relationships in the development of life forms with specialized functions.
Eukaryotic: Eukaryotic refers to organisms whose cells contain a nucleus and other membrane-bound organelles. This structure allows for more complex cellular functions compared to prokaryotic cells, leading to a diversity of life forms such as plants, animals, fungi, and protists. Eukaryotic cells are characterized by their larger size, compartmentalization, and a greater capacity for specialization.
Exon: An exon is a segment of DNA or RNA that codes for a portion of a protein. These sequences are important as they are expressed, or 'spliced' together during the process of transcription and translation to form mature messenger RNA (mRNA). Exons are interspersed with non-coding regions called introns, which are removed during RNA processing, highlighting their critical role in the overall flow of genetic information from DNA to functional proteins.
Gamete: A gamete is a specialized reproductive cell that carries genetic information and is involved in sexual reproduction. Gametes are haploid, meaning they contain only one set of chromosomes, which is crucial for maintaining the chromosome number during fertilization. When two gametes fuse during the process of fertilization, they create a diploid zygote, thus contributing to genetic diversity and inheritance patterns in offspring.
Gene: A gene is a segment of DNA that contains the instructions for producing a specific protein or set of proteins, which ultimately influence traits and functions in an organism. Genes are fundamental units of heredity, passed from parents to offspring, and play a critical role in the expression of characteristics in living organisms. They also interact with environmental factors to determine phenotypic traits.
Genes: Genes are segments of DNA that carry the instructions for the development, functioning, growth, and reproduction of all living organisms. They determine specific traits by encoding proteins or functional RNA molecules.
Genome: A genome is the complete set of genetic material present in an organism, including all of its genes and non-coding sequences. It serves as the blueprint for the organism's development, functioning, and reproduction, encompassing both the hereditary information inherited from parents and the variations that arise through mutation. The study of genomes allows scientists to understand evolutionary relationships, genetic disorders, and the complex regulatory mechanisms governing biological processes.
Haploid: Haploid refers to a cell or organism that has a single set of unpaired chromosomes, typically denoted as 'n'. This means that haploid cells contain half the number of chromosomes compared to diploid cells, which have paired sets. In the context of reproduction and genetic variation, haploid cells play a critical role, as they contribute to the formation of gametes in sexual reproduction and are fundamental to processes such as meiosis.
Histone: Histones are highly alkaline proteins found in the nuclei of eukaryotic cells that play a critical role in packaging DNA into a compact, organized structure known as chromatin. By wrapping around DNA, histones help condense the genetic material, enabling efficient storage and regulation of gene expression. They also play a part in the regulation of various cellular processes, including DNA replication and repair.
Incomplete dominance: Incomplete dominance is a genetic scenario where the phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes. This means that neither allele is completely dominant over the other, leading to a blend of traits in the offspring. This concept is crucial for understanding how traits are inherited and expressed, revealing the complexity of genetic interactions beyond simple dominant-recessive patterns.
Insertion: Insertion refers to a type of mutation where one or more nucleotide bases are added into a DNA sequence. This change can disrupt the reading frame of the gene, leading to significant alterations in the protein that is produced. Insertion mutations can have various effects on an organism, ranging from benign to potentially harmful, depending on where in the genome they occur and how they affect gene function.
Intron: An intron is a non-coding sequence of DNA that is found within a gene and is removed during the process of RNA splicing. Introns play a significant role in gene expression regulation and the generation of protein diversity by allowing for alternative splicing, which can produce different protein isoforms from the same gene. Their presence also impacts genomic structure and function, influencing how genes are organized within the genome.
Introns: Introns are non-coding sequences in a gene that are removed during RNA splicing. They do not encode protein sequences and are found in eukaryotic genomes.
Inversion: Inversion is a chromosomal rearrangement in which a segment of a chromosome is reversed end to end. This structural change can disrupt gene function and impact genetic expression, leading to various phenotypic consequences. Understanding inversions is important in the study of genetic diversity, evolution, and the mechanisms of certain genetic disorders.
Locus: A locus is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. This term is essential for understanding the organization of genes within the genome and how variations can affect genetic traits. The arrangement of loci can help identify chromosomal abnormalities and is crucial in the study of heredity, evolution, and genetic mapping.
Meiosis: Meiosis is a specialized form of cell division that reduces the chromosome number by half, resulting in four haploid cells, each genetically distinct from one another. This process is crucial for sexual reproduction, as it ensures genetic diversity and contributes to the formation of gametes, which are essential for fertilization.
Mendelian: Mendelian refers to the principles of inheritance first described by Gregor Mendel in the 19th century, which are foundational to understanding genetic inheritance. These principles explain how traits are passed from parents to offspring through discrete units known as genes, highlighting concepts like dominance, segregation, and independent assortment. The Mendelian framework laid the groundwork for modern genetics and helps in predicting the inheritance patterns of traits in organisms.
Mitochondria: Mitochondria are membrane-bound organelles found in eukaryotic cells, responsible for producing energy through cellular respiration. They are often referred to as the 'powerhouses' of the cell due to their role in ATP production.
Mitochondria: Mitochondria are membrane-bound organelles found in eukaryotic cells, often referred to as the 'powerhouses' of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. These organelles play a crucial role in energy metabolism and are involved in various biochemical processes, including the citric acid cycle and oxidative phosphorylation.
Mutagen: A mutagen is any agent that causes changes or mutations in the DNA sequence of an organism. These changes can lead to various effects, ranging from benign to serious health issues, including cancer. Mutagens can be physical agents like radiation, chemical substances, or even biological factors like viruses, and they play a significant role in understanding genetic mutations and their implications on the genome.
Mutation: A mutation is a change in the DNA sequence of an organism's genome, which can lead to variations in traits and can affect an organism's fitness in its environment. These changes can be caused by various factors, including environmental influences, replication errors during cell division, or even spontaneous alterations. Mutations are crucial for evolution, as they provide the raw genetic material upon which natural selection can act, leading to adaptations and evolutionary changes over time.
Nucleotide: A nucleotide is the basic building block of nucleic acids, such as DNA and RNA, consisting of a nitrogenous base, a five-carbon sugar, and one or more phosphate groups. Nucleotides play a crucial role in storing and transferring genetic information, forming the structure of DNA, and facilitating DNA replication.
Plasmid: A plasmid is a small, circular piece of DNA that exists independently of chromosomal DNA within a cell. These genetic structures are most commonly found in bacteria, where they can replicate independently and often carry genes that confer advantageous traits, such as antibiotic resistance. Plasmids play a significant role in the transfer of genetic material between organisms and are essential tools in molecular biology and genetic engineering.
Point Mutation: A point mutation is a change in a single nucleotide base pair in the DNA sequence, which can lead to variations in the protein produced or even no change at all. These mutations are crucial for understanding genetic diversity, evolution, and the underlying mechanisms of various diseases, including cancer. Point mutations can be classified into three main types: silent, missense, and nonsense mutations, each affecting the resulting protein differently.
Prokaryotic: Prokaryotic refers to a type of cell that lacks a distinct nucleus and membrane-bound organelles, making it simpler and typically smaller than eukaryotic cells. Prokaryotes, which include bacteria and archaea, have their genetic material in a single circular DNA molecule located in the nucleoid region, not enclosed by a nuclear membrane. This cellular structure allows prokaryotes to reproduce quickly and adapt to various environments.
Recessive: A recessive allele is a variant of a gene that does not manifest its trait in the presence of a dominant allele. This means that for a recessive trait to be expressed phenotypically, an individual must inherit two copies of the recessive allele, one from each parent. This concept is crucial for understanding genetic variation and inheritance patterns, as it highlights how traits can be passed down through generations even if they are not visibly expressed.
Recombination: Recombination is the exchange of genetic material between different chromosomes or between different regions within a chromosome. It increases genetic diversity by creating new combinations of genes.
Recombination: Recombination is the process by which genetic material is exchanged between chromosomes during meiosis, leading to the creation of new allele combinations in offspring. This process contributes to genetic diversity, allowing for a variety of traits within a population, which is essential for evolution and adaptation.
Sequencing: Sequencing refers to the process of determining the order of nucleotides in a DNA or RNA molecule. This technique is essential for understanding genetic information, gene expression, and how traits are inherited, providing a foundation for various applications in genomics, medicine, and evolutionary biology.
Substitution: Substitution refers to a type of mutation where one base pair in the DNA sequence is replaced by another. This can lead to changes in the amino acid sequence of a protein, potentially altering its function. The effects of substitution can vary widely, from having no effect on the protein's function to causing significant changes that may lead to disease.
Translocation: Translocation is the process where a segment of a chromosome is moved from one location to another within the genome. This can occur during cell division or due to genetic recombination and can lead to various genetic variations or diseases. Understanding translocation is crucial as it can influence gene expression and contribute to important biological processes.