https://www.khanacademy.org/science/ms-biology/x0c5bb03129646fd6:inheritance-and-variation/x0c5bb03129646fd6:chromosomes/v/chromosomes-and-genes 2022-10-19T00:04:19.365252683Z Chromosomes and genes Genes are located in the chromosomes of cells, with each chromosome pair containing two variants of each of many distinct genes. Khan Academy video https://cdn.kastatic.org/ka_thumbnails_cache/4a33b989-ccc9-447f-b93f-37b2a653269b_1280_720_base.png Chromosomes and genes Genes are located in the chromosomes of cells, with each chromosome pair containing two variants of each of many distinct genes. https://cdn.kastatic.org/ka-youtube-converted/taH5kyoQG0Q.mp4/taH5kyoQG0Q.mp4 204 DNA structure, replication, and stability https://www.khanacademy.org/science/ap-biology/cell-communication-and-cell-cycle/cell-cycle/a/dna-and-chromosomes-article 2021-04-29T07:55:56Z Chromosomes DNA, chromosomes, and genomes. Homologous chromosomes, sister chromatids, and haploid/diploid. article https://www.khanacademy.org/science/ms-biology/x0c5bb03129646fd6:inheritance-and-variation/x0c5bb03129646fd6:chromosomes/v/chromosome-pairs 2022-10-19T00:04:19.365252683Z Chromosome pairs Genes are located in the chromosomes of cells, with each chromosome pair containing two variants of each of many distinct genes. Khan Academy video https://cdn.kastatic.org/ka_thumbnails_cache/69038795-67b3-47a5-95cb-e3131b831272_1280_720_base.png Chromosome pairs Genes are located in the chromosomes of cells, with each chromosome pair containing two variants of each of many distinct genes. https://cdn.kastatic.org/ka-youtube-converted/SbagR2CpP_o.mp4/SbagR2CpP_o.mp4 217 DNA structure, replication, and stability https://www.khanacademy.org/science/ms-biology/x0c5bb03129646fd6:inheritance-and-variation/x0c5bb03129646fd6:chromosomes/a/chromosomes-and-genes-ms 2026-02-27T17:50:36.702607024Z Chromosomes and genes Review your understanding of chromosomes and genes in this free article aligned to NGSS standards. article https://www.khanacademy.org/science/ms-biology/x0c5bb03129646fd6:inheritance-and-variation/x0c5bb03129646fd6:chromosomes/a/chromosome-pairs 2022-07-28T07:36:12.049762406Z Chromosome pairs Review your understanding of chromosome pairs in this free article aligned to NGSS standards. article https://www.khanacademy.org/science/biology/dna-as-the-genetic-material/dna-discovery-and-structure/v/hershey-and-chase-conclusively-show-dna-genetic-material 2022-09-22T01:27:37.241774086Z Hershey and Chase: DNA is the genetic material How Alfred Hershey and Martha Chase showed conclusively that DNA is the genetic material. video https://cdn.kastatic.org/googleusercontent/V7zXKSFCCH3LJKNrcfTAktrLtNdgxPOhCDE3l0r-D7DIB_9UOatHO8F166fIIMCix9DP4WeXeOSvdYZVwXCwKldi6g Hershey and Chase: DNA is the genetic material How Alfred Hershey and Martha Chase showed conclusively that DNA is the genetic material. https://cdn.kastatic.org/ka-youtube-converted/bNsSaxCsIIg.mp4/bNsSaxCsIIg.mp4 529 DNA structure, replication, and stability https://www.khanacademy.org/science/ka-biology-grade-12/x406cf103e0507862:in-in-the-molecular-basis-of-inheritance/x406cf103e0507862:in-in-discovery-of-dna-as-the-genetic-material/e/discovery-of-dna 2023-09-11T02:49:35.584738689Z Discovery of DNA Test your knowledge on the events and people involved in the discovery of DNA! Ashley exercise https://www.khanacademy.org/science/biology/dna-as-the-genetic-material/dna-discovery-and-structure/a/classic-experiments-dna-as-the-genetic-material 2021-04-29T07:53:44Z Classic experiments: DNA as the genetic material Experiments by Frederick Griffith, Oswald Avery and his colleagues, and Alfred Hershey and Martha Chase. article https://www.khanacademy.org/science/biology/dna-as-the-genetic-material/dna-discovery-and-structure/v/the-discovery-of-the-double-helix-structure-of-dna 2022-09-22T01:27:37.241774086Z The discovery of the double helix structure of DNA How the double helix structure of DNA was discovered. Work of Watson, Crick, Franklin, Wilkins, and Chargaff. video https://cdn.kastatic.org/googleusercontent/Nu1myZ1Zd131-3IKC8dUtwtqqCta6MwX00wpeYfY59jbYKoWpsDMCirekr_dROR0FcuAeKx2AZ8KsWEwhpy29ef6 The discovery of the double helix structure of DNA How the double helix structure of DNA was discovered. Work of Watson, Crick, Franklin, Wilkins, and Chargaff. https://cdn.kastatic.org/ka-youtube-converted/hCUce36Ganc.mp4/hCUce36Ganc.mp4 537 DNA structure, replication, and stability https://www.khanacademy.org/science/biology/dna-as-the-genetic-material/dna-discovery-and-structure/a/discovery-of-the-structure-of-dna 2023-09-14T11:07:34.466749579Z Discovery of the structure of DNA The structure of DNA double helix and how it was discovered. Chargaff, Watson and Crick, and Wilkins and Franklin. article https://www.khanacademy.org/science/ap-biology/gene-expression-and-regulation/replication/v/semi-conservative-replication 2025-07-21T19:27:31.703149266Z Semi-conservative replication DNA replication has three possible methods: conservative, dispersive, and semi-conservative. Here, we focus on the Meselson-Stahl experiment, which proved DNA replication is semi-conservative. In this process, each new DNA pair consists of one old strand and one new strand, ensuring accurate genetic information transfer. Efrat Bruck video https://cdn.kastatic.org/googleusercontent/dZCvnvHg5mTDZqxBZSxDyl-FSuSZ9wO6T6HcK-SL1eRhapMjBD9J_bAzBZc4-JsvRHMmhv9afXn-oIulASN-OjlF Semi-conservative replication DNA replication has three possible methods: conservative, dispersive, and semi-conservative. Here, we focus on the Meselson-Stahl experiment, which proved DNA replication is semi-conservative. In this process, each new DNA pair consists of one old strand and one new strand, ensuring accurate genetic information transfer. https://cdn.kastatic.org/ka-youtube-converted/jaJ3NlqK5dA.mp4/jaJ3NlqK5dA.mp4 132 DNA structure, replication, and stability https://www.khanacademy.org/science/biology/dna-as-the-genetic-material/dna-replication/a/mode-of-dna-replication-meselson-stahl-experiment 2023-09-14T11:07:34.466749579Z Mode of DNA replication: Meselson-Stahl experiment A key historical experiment that demonstrated the semi-conservative mechanism of DNA replication. article https://www.khanacademy.org/science/ap-biology/gene-expression-and-regulation/replication/v/leading-and-lagging-strands-in-dna-replication 2023-12-04T19:02:25.924542584Z Leading and lagging strands in DNA replication DNA replication is a precise process where DNA unwinds and splits into two strands. Each strand then serves as a template for a new DNA molecule. The leading strand is built continuously, while the lagging strand is built in fragments, called Okazaki fragments. Sal Khan video https://cdn.kastatic.org/ka_thumbnails_cache/4246e827-19f5-4ce4-92e8-8cb36b5638a8_1280_720_base.png Leading and lagging strands in DNA replication DNA replication is a precise process where DNA unwinds and splits into two strands. Each strand then serves as a template for a new DNA molecule. The leading strand is built continuously, while the lagging strand is built in fragments, called Okazaki fragments. https://cdn.kastatic.org/ka-youtube-converted/eM7arWJJ3zk.mp4/eM7arWJJ3zk.mp4 619 DNA structure, replication, and stability https://www.khanacademy.org/science/ap-biology/gene-expression-and-regulation/replication/e/replication 2025-11-24T21:00:40.80360556Z Replication Test your knowledge of replication! Megan Cohn exercise https://www.khanacademy.org/science/ap-biology/gene-expression-and-regulation/replication/a/hs-dna-structure-and-replication-review 2021-04-29T07:52:23Z DNA structure and replication review article https://www.khanacademy.org/science/biology/dna-as-the-genetic-material/dna-replication/a/telomeres-telomerase 2025-06-30T13:17:39.587845569Z Telomeres and telomerase Telomeres as protective "caps" on the tips of eukaryotic chromosomes. How telomerase extends telomeres. article https://www.khanacademy.org/science/ap-biology/gene-expression-and-regulation/replication/v/speed-and-precision-of-dna-replication 2023-06-22T09:32:02.370557018Z Speed and precision of DNA replication DNA replication is a complex, fast, and precise process involving enzymes like topoisomerase, helicase, and polymerase. In E. coli, polymerase can replicate up to 700+ base pairs per second. Initially, one mistake occurs for every 10 million nucleotides, but proofreading reduces errors to one in a billion. This amazing cellular machinery keeps our DNA accurate and functional. Sal Khan video https://cdn.kastatic.org/ka_thumbnails_cache/9b526092-5e87-40f7-8a89-f19bbba2fd74_1280_720_base.png Speed and precision of DNA replication DNA replication is a complex, fast, and precise process involving enzymes like topoisomerase, helicase, and polymerase. In E. coli, polymerase can replicate up to 700+ base pairs per second. Initially, one mistake occurs for every 10 million nucleotides, but proofreading reduces errors to one in a billion. This amazing cellular machinery keeps our DNA accurate and functional. https://cdn.kastatic.org/ka-youtube-converted/PSl6IXUCNuw.mp4/PSl6IXUCNuw.mp4 235 DNA structure, replication, and stability https://www.khanacademy.org/science/ap-biology/gene-expression-and-regulation/replication/a/molecular-mechanism-of-dna-replication 2023-08-07T17:09:37.131449861Z Molecular mechanism of DNA replication Roles of DNA polymerases and other replication enzymes. Leading and lagging strands and Okazaki fragments. article https://www.khanacademy.org/science/biology/dna-as-the-genetic-material/dna-replication/a/dna-proofreading-and-repair 2021-04-29T07:52:50Z DNA proofreading and repair Mechanisms to correct errors during DNA replication and to repair DNA damage over the cell's lifetime. article