Slide 1

Topic: Genetics and Evolution - Molecular Basis of Inheritance

• The molecular basis of inheritance refers to the role of DNA and RNA in passing down genetic information from one generation to another.
• DNA carries the genetic code, while RNA helps in the synthesis of proteins.
• Nucleotides are the building blocks of DNA and RNA.
• The genetic code is determined by the sequence of nucleotides in DNA.
• How many nucleotides are necessary to specify a single amino acid?

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Nucleotides and DNA Structure

• Nucleotides are composed of three main components: a sugar molecule, a phosphate group, and a nitrogenous base.
• DNA (deoxyribonucleic acid) is a double-stranded molecule made up of nucleotides.
• The sugar molecule in DNA is called deoxyribose.
• There are four types of nitrogenous bases in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G).
• The order of these bases in DNA determines the genetic information.

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Complementary Base Pairing

• In DNA, adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G).
• This is known as complementary base pairing.
• The two strands of DNA are held together by hydrogen bonds between the base pairs.
• Complementary base pairing ensures that DNA can be accurately replicated and transcribed.

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DNA Replication

• DNA replication is the process by which DNA is copied to produce two identical DNA molecules.
• It occurs during the S phase of the cell cycle.
• The enzyme DNA helicase unwinds the double helix, separating the two strands.
• DNA polymerase adds complementary nucleotides to each of the original strands.
• The result is two identical DNA molecules, each with one original strand and one newly synthesized strand.

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Transcription

• Transcription is the process by which DNA is used as a template to produce RNA.
• It takes place in the nucleus of eukaryotic cells.
• The enzyme RNA polymerase binds to the DNA and separates the two strands.
• RNA polymerase adds complementary nucleotides to the growing RNA strand.
• The end result is a single-stranded RNA molecule that is complementary to the DNA sequence.

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Types of RNA

• There are three main types of RNA: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
• mRNA carries the genetic code from the DNA to the ribosomes.
• tRNA brings amino acids to the ribosomes during protein synthesis.
• rRNA is a structural component of the ribosomes, where protein synthesis occurs.

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Genetic Code

• The genetic code is the set of rules by which the sequence of nucleotides in DNA or mRNA is translated into the sequence of amino acids in a protein.
• The genetic code is degenerate, meaning that each amino acid can be coded for by multiple codons.
• There are a total of 64 codons, including start and stop codons.
• AUG is the start codon, which codes for the amino acid methionine.
• UAA, UAG, and UGA are stop codons, which signal the end of protein synthesis.

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Translation

• Translation is the process by which the genetic code in mRNA is used to synthesize proteins.
• It takes place in the ribosomes.
• The mRNA attaches to the ribosome, and the ribosome reads the mRNA codons.
• tRNA molecules bring the appropriate amino acids to the ribosome, based on the codons in the mRNA.
• The amino acids are joined together to form a polypeptide chain.

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Protein Synthesis

• Protein synthesis is the process by which cells build proteins.
• It involves both transcription and translation.
• Transcription occurs in the nucleus, where mRNA is produced from DNA.
• mRNA then moves to the ribosomes in the cytoplasm, where translation takes place.
• During translation, the genetic code in mRNA is used to assemble amino acids into a protein.

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Central Dogma of Molecular Biology

• The central dogma of molecular biology describes the flow of genetic information in cells.
• According to the central dogma, information can flow from DNA to DNA, DNA to RNA, or RNA to protein.
• DNA replication copies DNA molecules.
• Transcription converts DNA into RNA.
• Translation synthesizes proteins from RNA.

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• The genetic code is a triplet code, meaning that three nucleotides (a codon) specify one amino acid.
• There are 20 different amino acids, yet there are 64 different codons.
• This means that some amino acids can be specified by more than one codon.
• The genetic code is universal, meaning that the same codons specify the same amino acids in all living organisms.
• For example, the codons GCU, GCC, GCA, and GCG all specify the amino acid alanine.

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• Mutations are changes in the DNA sequence that can result in alterations to the genetic code.
• There are two main types of mutations: point mutations and chromosomal mutations.
• Point mutations involve a change in a single nucleotide.
• There are three types of point mutations: substitutions, insertions, and deletions.
• Substitutions involve the replacement of one nucleotide with another.

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• Insertions and deletions involve the addition or removal of one or more nucleotides, respectively.
• These mutations can have significant effects on the resulting protein.
• Insertions and deletions can cause a frameshift, where the reading frame of the codons is shifted.
• This can lead to the production of non-functional or completely different proteins.

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• Chromosomal mutations involve changes in the structure or number of chromosomes.
• There are several types of chromosomal mutations, including deletions, duplications, inversions, and translocations.
• Deletions involve the loss of a portion of a chromosome.
• Duplications occur when a portion of a chromosome is repeated.
• Inversions involve the reversal of a portion of a chromosome.

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• Translocations occur when a portion of one chromosome breaks off and attaches to another chromosome.
• Chromosomal mutations can have severe consequences and are often associated with genetic disorders.
• Examples include Down syndrome, caused by an extra copy of chromosome 21, and Turner syndrome, caused by a missing or incomplete second sex chromosome.

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Examples of Genetic Disorders

• Cystic Fibrosis: caused by mutations in the CFTR gene, resulting in the production of thick, sticky mucus in the lungs and digestive system.
• Huntington’s Disease: caused by a mutation in the HTT gene, resulting in the progressive breakdown of nerve cells in the brain.
• Sickle Cell Disease: caused by a mutation in the HBB gene, resulting in the production of abnormal hemoglobin, causing red blood cells to become misshapen.

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Cancer and Genetics

• Cancer is a complex disease caused by a combination of genetic and environmental factors.
• Mutations in specific genes, known as oncogenes and tumor suppressor genes, can increase the risk of cancer.
• Oncogenes promote cell division and growth, while tumor suppressor genes regulate these processes.
• Mutations in these genes can lead to uncontrolled cell growth and the development of tumors.

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Genetic Screening and Counseling

• Genetic screening involves testing individuals for genetic disorders or the risk of developing certain diseases.
• This can help individuals make informed decisions about their health and reproductive choices.
• Genetic counseling provides information and support to individuals and families who may be at risk for inheritable disorders.
• It can help individuals understand the risk factors, make decisions about testing, and plan for the future.

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Genetic Engineering

• Genetic engineering involves manipulating an organism’s genes to achieve desired traits or outcomes.
• This can be done through techniques such as gene cloning, gene editing, and genetic modification.
• Genetic engineering has applications in various fields, including agriculture, medicine, and industry.
• Examples include genetically modified crops that are resistant to pests or diseases, and gene therapy to treat genetic disorders.

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Conclusion

• The molecular basis of inheritance plays a fundamental role in genetics and evolution.
• DNA replication, transcription, and translation are key processes in the flow of genetic information.
• Mutations can lead to genetic disorders and diseases.
• Understanding genetics and genetic engineering has significant implications for medicine, agriculture, and society as a whole.
• By studying and unraveling the molecular basis of inheritance, we can gain a deeper understanding of the complexity and diversity of life on Earth.

Slide 21

• A single amino acid is specified by a triplet of nucleotides called a codon.
• There are a total of 64 possible codons formed by different combinations of A, C, G, and T.
• Therefore, at least three nucleotides are necessary to specify a single amino acid.
• For example, the codon GAA specifies the amino acid glutamic acid.

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• Mutations can occur spontaneously or as a result of exposure to mutagens, such as radiation or certain chemicals.
• Some mutations can be beneficial, providing organisms with an advantage in certain environments.
• Genetic variation caused by mutations is important for evolution to occur.
• However, mutations can also cause genetic disorders and diseases.

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• Multiple mutations can accumulate over time, leading to genetic diversity within a population.
• Genetic diversity is crucial for a species’ ability to adapt and survive in changing environments.
• Without genetic diversity, a population may become more susceptible to diseases or other threats.

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• The study of genetics helps us understand the inheritance and transmission of traits from one generation to another.
• It also enables us to study the evolutionary relationships between different species.
• Genetic analysis can be used to determine paternity, identify disease-causing genes, and study population genetics.

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• Gregor Mendel is considered the father of modern genetics.
• In the mid-19th century, he conducted experiments with pea plants and discovered the basic principles of inheritance.
• Mendel’s findings formed the foundation for our understanding of dominance, segregation, and independent assortment of genetic traits.

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• A Punnett square is a tool used to predict the possible outcomes of a cross between two individuals with known genotypes.
• It shows the different combinations of alleles that can result from a mating and their respective probabilities.
• The Punnett square is a useful tool in studying monohybrid and dihybrid crosses.

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• Genotype refers to the genetic makeup of an individual, which can be expressed as a combination of alleles.
• Phenotype refers to the observable traits or characteristics of an individual.
• Genotype influences phenotype, but other factors such as environmental conditions can also play a role.

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• Co-dominance is a form of inheritance where both alleles for a specific trait are simultaneously expressed in the heterozygous condition.
• An example of co-dominance is the ABO blood group system, where both A and B alleles are expressed in individuals with AB blood type.

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• Incomplete dominance is a form of inheritance where the heterozygous phenotype is intermediate between the phenotypes of the homozygous individuals.
• An example of incomplete dominance is the inheritance of flower color in snapdragons, where red and white alleles produce pink flowers in heterozygotes.

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• Polygenic inheritance refers to the inheritance of a trait that is controlled by multiple genes, each contributing a small effect on the phenotype.
• Examples of polygenic traits include height, skin color, and intelligence.
• Polygenic traits often show a continuous range of phenotypes instead of discrete categories.

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