9.5. Ligation and recombination

Ligation and recombination

Morgan received the Nobel Prize in 1934 for proving chromosome theory with his laboratory work with the fruit fly Drosophila melanogaster studying the transmission of the "eye color" character.

The Drosophila melanogaster normally has a bright red eye color, but a white-eyed male was discovered. When the male (white eyes) crossed with the normal females (red eyes), all the offspring had red eyes. This was to be expected if it is a dominant inheritance.

When he crossed individuals of F₁ (red eyes) he obtained a progeny of 3 (red eyes) by 1 (white eyes), but in which all the white-eyed flies were male.

If it was a reciprocal cross, white - eyed females with male red - eyed, got offspring with all females of the F₁ with red eyes, and all males with white eyes.

Morgan related this type of inheritance, in which males inherit the character from the mother and females from the father, with sex. He hypothesized that alleles for eye color (red or white) would be located on the X chromosome, with no information for that trait on the Y chromosome. Females would have two alleles for that gene, but males only one. This would explain the existence of sex-linked characters and that genes are located on chromosomes.

By GYassineMrabetTalk✉This vector image was created with Inkscape. (Own work) [GFDL or CC BY-SA 3.0], via Wikimedia Commons

Ligation

Any species has few chromosomes compared to the number of characters, so each chromosome has to contain many genes.

Genes that are on different chromosomes are distributed among the gametes independently of each other, but genes located very closely on the same chromosome tend to be inherited together, which is why they are called linked genes. They can be linked on both autosomes and sex chromosomes.

Logically, if they are linked genes, the phenotypic proportions obtained in their crosses will be different.

For example, when a test cross (AaBb * aabb) is performed in a diheterozygous individual (AaBb) , the result, if they are not linked genes, is an offspring with a 1:1:1:1 ratio (AB:Ab:aB:ab). But if it is a question of linked genes, the phenotypic ratio obtained would be 1:1, since the genes tend to be transmitted together.

If the result obtained is very different from the 1:1:1:1 ratio, it can make us think that there is linkage between the genes. But that genes are linked does not mean that they are always transmitted together, since homologous chromatids, in meiotic prophase I, exchange chromosomal fragments in recombination. Then, the same phenotypes are obtained as the parental ones (those with the highest frequency) and others, less frequent, which are the recombinant ones.

Recombination

As we saw when talking about meiosis, each chromosome is duplicated and two identical sister chromatids are obtained . Homologous chromosomes pair (synapse) and cross-over occurs between non-sister chromatids (from two different chromosomes). Two of these four chromatids break and join at any point, exchanging genetic material. Thus, there are two chromatids that remain intact, have not crossed over, which are called non-recombinant or parental type, and two other chromatids that are recombinant .

Limits of recombination

When two loci are so far apart within the same chromosome that there is a 100% chance that a chiasm will form between them, they will produce phenotypes similar to what they would if they were on different chromosomes. That is, 50% of the gametes will be of the parental type (non-recombinant) and 50% of the recombinant type.

The frequency of recombination between two linked genes is constant and characteristic of that pair of genes. It cannot exceed 50%, even when there are multiple crossovers between them. The frequency of recombination increases the further apart these genes are, since the length of the chromosome fragment in which the crossover can occur is greater.

Making a chromosome map

If you know the crossover frequency between two genes, you can know the distance between them, and therefore the position (locus) that each gene occupies within the chromosome.

The recombination unit (or map unit) is called centimorgan, and it is equivalent to the distance between two points on the chromosome, whose recombination frequency will be 1%.

With the data of distances between the genes, chromosome maps can be made, which contain the genetic information of the species.

Puzzle: Encuentra la Drosophila melanogaster.

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Skip navigation Biology 2nd Baccalaureate Biology 2nd Bac. 1. Bioelements and biomolecules. Water and mineral salts 1.1. Chemical bonds in biology 1.1.1. Intramolecular bonds 1.1.1.1. Covalent bond 1.1.1.2. Ionic bond 1.1.2. Intermolecular bonds 1.1.2.1. Van der Waals forces 1.1.2.2. Hydrogen bonds 1.2. The chemical basis of life: inorganic and organic components 1.2.1. Primary bioelements 1.2.2. Secondary bioelements 1.2.3. Trace elements 1.3. The immediate principles or biomolecules 1.3.1. Water 1.3.1.1. Chemical structure of water 1.3.1.2. Properties and functions of water 1.3.2. Mineral salts 1.3.2.1. Functions of salts in solution 1.3.2.2. Colloidal solutions and dispersions 1.3.2.3. Properties of colloidal dispersions 1.3.2.4. Diffusion, osmosis and dialysis 1.3.2.4.1. Diffusion 1.3.2.4.2. Osmosis 1.3.2.4.3. Dialysis 1.4. Bibliography 2. Glucides 2.1. Glucid concept 2.2. Classification of carbohydrates 2.3. Monosaccharides 2.3.1. Trioses 2.3.1.1. Spatial isomerism or stereoisomerism 2.3.2. Tetroses 2.3.3. Pentoses 2.3.3.1. Monosaccharide cyclization 2.3.4. Hexoses 2.4. The N-glucosidic and O-glucosidic bonds 2.4.1. Substances derived from monosaccharides 2.5. Disaccharides 2.6. Polysaccharides 2.6.1. Homopolysaccharides 2.6.1.1. Reserve homopolysaccharides 2.6.1.2. Structural homopolysaccharides 2.6.2. Heteropolysaccharides 2.6.3. Heterosides 2.7. General functions of glucides 2.8. Bibliography 3. Lipids 3.1. Lipid concept 3.2. Classification of lipids 3.2.1. Fatty acids 3.2.1.1. Saturated and unsaturated fatty acids 3.2.1.2. Chemical properties of fatty acids 3.2.1.3. Physical properties of fatty acids 3.2.1.4. Fatty Acid Functions 3.2.2. Saponifiable lipids or with fatty acids 3.2.2.1. Simple lipids 3.2.2.1.1. Acylglycerides 3.2.2.1.2. Cerides 3.2.2.2. Complex lipids 3.2.2.2.1. Phospholipids 3.2.2.2.2. Glycolipids 3.2.3. Unsaponifiable lipids or without fatty acids 3.3. Lipid functions 3.4. Bibliography 4. Proteins 4.1. Introduction to proteins 4.2. Amino acids 4.2.1. Classification of amino acids 4.2.2. Properties of amino acids 4.3. The peptide bond 4.4. Protein 4.4.1. Protein structure 4.4.1.1. Primary structure of proteins 4.4.1.2. Secondary structure of proteins 4.4.1.3. Tertiary structure of proteins 4.4.1.4. Quaternary structure of proteins 4.4.2. Protein properties 4.4.3. Classification of proteins 4.4.3.1. Holoproteins 4.4.3.2. Heteroproteins 4.4.4. Protein functions 4.5. Enzymes 4.5.1. Structure of enzymes 4.5.2. The active center of enzymes 4.5.3. General Mechanism of Enzyme Catalysis 4.5.4. Regulation of enzyme activity 4.5.5. Allosteric enzymes 4.5.6. Nomenclature and classification of enzymes 4.6. The vitamins 4.6.1. Fat-soluble vitamins 4.6.2. Water soluble vitamins 4.7. Bibliography 5. Nucleotides and nucleic acids 5.1. The chemical composition of nucleic acids 5.1.1. Components of nucleic acids 5.1.2. Concept, types and functions of nucleic acids 5.1.3. Nucleosides 5.1.4. Nucleotides 5.1.4.1. Nucleotide functions 5.1.5. Nucleic acids 5.2. Deoxyribonucleic acid (DNA) 5.2.1. DNA structure 5.2.1.1. Primary structure of DNA 5.2.1.2. Secondary structure of DNA 5.2.1.3. Tertiary structure of DNA 5.2.1.3.1. Tertiary structure of DNA in prokaryotes 5.2.1.3.2. Tertiary structure of DNA in eukaryotes 5.2.1.4. Quaternary structure of DNA 5.2.2. DNA types 5.2.3. Genetic material: chromatin and chromosomes 5.2.3.1. Karyotype and karyogram 5.3. Ribonucleic acid (RNA) 5.3.1. RNA types 5.3.1.1. Transfer RNA 5.3.1.2. Messenger RNA 5.3.1.3. Ribosomal RNA 5.3.1.4. Nucleolar RNA 5.3.1.5. Small nuclear RNA 5.3.2. Functions of ribonucleic acids 5.4. Bibliography 6. Cell morphology 6.1. Cell concept 6.1.1. Cell history 6.1.2. Cell theory 6.2. Levels of cellular organization 6.2.1. General characteristics of cells 6.2.2. Prokaryotic cells 6.2.2.1. Prokaryotic cell morphology 6.2.2.2. Structure of prokaryotes 6.2.2.2.1. Bacterial capsule 6.2.2.2.2. Bacterial wall 6.2.2.2.3. Plasma membrane 6.2.2.2.4. Cytoplasm-Ribosomes-Inclusions 6.2.2.2.5. Bacterial DNA 6.2.2.2.6. Bacterial appendages 6.2.2.3. Bacteria Physiology 6.2.3. Eukaryotic cells 6.2.3.1. Animal and plant cell 6.2.3.1.1. Animal eukaryotic cell 6.2.3.1.2. Plant eukaryotic cell 6.2.3.2. Cell Evolution: Endosymbiont Theory 6.3. Size, shape and quantity 6.4. The plasma membrane 6.4.1. Chemical composition of the membrane 6.4.2. The structure of the membrane. The fluid mosaic model 6.4.3. Functions of the plasma membrane 6.4.4. Transport across the membrane 6.4.4.1. Small molecule transport 6.4.4.2. Macromolecule transport 6.4.5. Plasma membrane differentiations 6.5. The cell wall of plant cells 6.5.1. Chemical composition of the cell wall 6.5.2. Cell wall structure 6.5.3. Cell wall differentiations 6.5.4. Cell wall functions 6.6. Extracellular matrix or glucocalyx 6.7. Cytosol or hyaloplasm 6.8. The cytoskeleton 6.8.1. Microfilaments or actin filaments 6.8.2. Intermediate filaments 6.8.3. Microtubules 6.9. Cell membrane and organelle systems 6.9.1. Membrane systems 6.9.1.1. The endoplasmic reticulum 6.9.1.2. Golgi apparatus 6.9.2. Cell organelles 6.9.2.1. Lysosomes 6.9.2.2. Peroxisomes 6.9.2.3. Vacuoles 6.9.2.4. Mitochondria 6.9.2.4.1. Functions of the mitochondria 6.9.2.5. Plastids 6.9.2.5.1. Chloroplasts 6.9.2.6. Ribosomes 6.9.2.7. Centrosome 6.9.2.8. Cilia and flagella 6.10. Cell motility 6.11. The cell nucleus 6.11.1. Characteristics of the cell nucleus 6.11.2. The interphase nucleus 6.11.3. The mitotic nucleus or nucleus in division 6.12. Bibliography 7. Metabolism 7.1. Metabolism 7.1.1. Energetic Aspects of Cellular Chemical Reactions 7.2. Catabolism 7.2.1. Catabolism and obtaining energy 7.2.2. Carbohydrate catabolism 7.2.2.1. Glycolysis 7.2.2.2. Cellular respiration 7.2.2.2.1. Oxidative decarboxylation 7.2.2.2.2. Krebs cycle 7.2.2.2.3. Electron transport chain 7.2.2.2.4. Energy balance of cellular respiration 7.2.2.3. Fermentations 7.2.2.3.1. Alcoholic or ethyl fermentation 7.2.2.3.2. Lactic fermentation 7.2.2.3.3. Other types of fermentations 7.3. Anabolism 7.3.1. Autotrophic anabolism 7.3.2. Photosynthesis 7.3.2.1. Photochemical or light phase 7.3.2.1.1. Photosystems 7.3.2.1.2. Photophosphorylation 7.3.2.1.2.1. Non cyclic photophosphorylation 7.3.2.1.2.2. Cyclic photophosphorylation 7.3.2.2. Biosynthetic or dark phase 7.3.2.3. Factors influencing photosynthesis 7.3.2.4. Products of photosynthesis 7.3.3. Chemosynthesis 7.4. Bibliography 8. Cell reproduction 8.1. The cell cycle 8.1.1. Interphase 8.1.2. Cellular division 8.2. Cellular division 8.2.1. Mitosis 8.2.1.1. Prophase 8.2.1.2. Metaphase 8.2.1.3. Anaphase 8.2.1.4. Telophase 8.2.1.5. Cytokinesis 8.2.1.6. More on mitosis 8.2.2. Meiosis 8.2.2.1. Meiosis I 8.2.2.2. Meiosis II 8.2.3. Meiosis and sexual reproduction 8.2.4. Meiosis and life cycle 8.2.5. Biological importance of meiosis 8.3. Differences and similarities between mitosis and meiosis 8.4. Bibliography 9. Classical genetics 9.1. Genetics basics 9.2. Mendelian genetics 9.2.1. The method 9.2.2. Mendel's Laws 9.2.2.1. Mendel's first law or principle of uniformity in the first generation 9.2.2.2. Mendel's second law or principle of segregation 9.2.2.2.1. Backcross and test crossover 9.2.2.3. Mendel's third law or principle of independent combination 9.3. Gene interaction 9.3.1. Gene interaction between allelic genes 9.3.2. Gene interaction between non-allelic genes that influence for the same trait 9.4. Chromosomal theory of heredity 9.5. Ligation and recombination 9.6. Complex mendelism 9.6.1. Multiple allelism 9.6.1.1. Lethal genes 9.6.2. Pleiotropy 9.6.3. Expressiveness and genetic penetrance 9.7. Sex-linked inheritance 9.7.1. Y-linked inheritance 9.7.2. X-linked inheritance 9.8. Heredity influenced by sex 9.9. Bibliography 10. Molecular genetics 10.1. DNA as hereditary material 10.2. DNA replication 10.2.1. The need for DNA replication 10.2.2. First hypotheses about DNA duplication 10.2.3. Meselson and Stahl experiment 10.2.4. The sense of growth of the new strands 10.2.5. Mechanism of DNA replication 10.2.5.1. Replication in prokaryotes 10.2.5.2. Replication in eukaryotes 10.2.6. Error correction 10.2.7. Enzymes involved in replication 10.3. Gene concept 10.4. "One gene-one enzyme" theory 10.5. Transcription 10.5.1. Mechanism of transcription 10.5.1.1. Transcription in prokaryotes 10.5.1.2. Eukaryotic transcription 10.6. Translation or protein biosynthesis 10.6.1. The genetic code 10.6.2. Mechanism of translation of RNA to proteins 10.6.2.1. Translation in eukaryotes 10.7. Regulation of gene expression 10.8. Bibliography 11. Genetics and evolution 11.1. Mutations 11.2. Types of mutations 11.2.1. Gene or point mutation 11.2.2. Chromosomal or structural mutation 11.2.3. Mutation at the genomic level 11.3. Causes of mutations 11.4. Evolutionary implications of mutations 11.5. Metabolic implications of mutations 11.6. Bibliography 12. Microbiology and biotechnology 12.1. Microbiology 12.2. Viruses 12.2.1. Viral morphology 12.2.2. Viral physiology 12.2.2.1. Lytic cycle 12.2.2.2. Lysogenic cycle 12.2.2.3. Cycles of viruses of special interest 12.2.2.3.1. Flu virus life cycle 12.2.2.3.2. Life cycle of the AIDS virus 12.3. Other acellular forms 12.3.1. Viroids 12.3.2. Prions 12.4. Biotechnology 12.5. Bibliography 13. Immunology 13.1. Infection concept 13.2. Defense mechanisms against infections 13.2.1. Nonspecific mechanisms 13.2.1.1. Primary barriers: external defenses 13.2.1.2. Secondary barriers: internal defenses 13.2.2. Specific mechanisms 13.3. Immunity and immune system 13.3.1. Components of the immune system 13.3.2. Concept and nature of antigens 13.4. The immune response 13.4.1. Humoral immune response: the antibodies 13.4.1.1. Antibody-producing cells: B lymphocytes 13.4.1.2. Antibodies 13.4.1.2.1. Types of antibodies 13.4.1.2.2. Antigen-antibody reaction 13.4.1.3. Immune memory: primary and secondary responses 13.4.2. Cellular immune response: T lymphocytes 13.5. Types of immunity 13.5.1. Natural immunity 13.5.2. Artificial immunity 13.6. Immune system disorders 13.6.1. Autoimmunity 13.6.2. Hypersensitivity 13.6.3. Immunodeficiency 13.6.4. Transplants and the phenomenon of rejections 13.7. Bibliography « Previous \| Next » 9.5. Ligation and recombination Ligation and recombination Morgan received the Nobel Prize in 1934 for proving chromosome theory with his laboratory work with the fruit fly Drosophila melanogaster studying the transmission of the "eye color" character. The Drosophila melanogaster normally has a bright red eye color, but a white-eyed male was discovered. When the male (white eyes) crossed with the normal females (red eyes), all the offspring had red eyes. This was to be expected if it is a dominant inheritance. When he crossed individuals of F₁ (red eyes) he obtained a progeny of 3 (red eyes) by 1 (white eyes), but in which all the white-eyed flies were male. If it was a reciprocal cross, white - eyed females with male red - eyed, got offspring with all females of the F₁ with red eyes, and all males with white eyes. Morgan related this type of inheritance, in which males inherit the character from the mother and females from the father, with sex. He hypothesized that alleles for eye color (red or white) would be located on the X chromosome, with no information for that trait on the Y chromosome. Females would have two alleles for that gene, but males only one. This would explain the existence of sex-linked characters and that genes are located on chromosomes. By GYassineMrabetTalk✉This vector image was created with Inkscape. (Own work) [GFDL or CC BY-SA 3.0], via Wikimedia Commons Ligation Any species has few chromosomes compared to the number of characters, so each chromosome has to contain many genes. Genes that are on different chromosomes are distributed among the gametes independently of each other, but genes located very closely on the same chromosome tend to be inherited together, which is why they are called linked genes. They can be linked on both autosomes and sex chromosomes. Logically, if they are linked genes, the phenotypic proportions obtained in their crosses will be different. For example, when a test cross (AaBb * aabb) is performed in a diheterozygous individual (AaBb) , the result, if they are not linked genes, is an offspring with a 1:1:1:1 ratio (AB:Ab:aB:ab). But if it is a question of linked genes, the phenotypic ratio obtained would be 1:1, since the genes tend to be transmitted together. If the result obtained is very different from the 1:1:1:1 ratio, it can make us think that there is linkage between the genes. But that genes are linked does not mean that they are always transmitted together, since homologous chromatids, in meiotic prophase I, exchange chromosomal fragments in recombination. Then, the same phenotypes are obtained as the parental ones (those with the highest frequency) and others, less frequent, which are the recombinant ones. Recombination As we saw when talking about meiosis, each chromosome is duplicated and two identical sister chromatids are obtained . Homologous chromosomes pair (synapse) and cross-over occurs between non-sister chromatids (from two different chromosomes). Two of these four chromatids break and join at any point, exchanging genetic material. Thus, there are two chromatids that remain intact, have not crossed over, which are called non-recombinant or parental type, and two other chromatids that are recombinant . Limits of recombination When two loci are so far apart within the same chromosome that there is a 100% chance that a chiasm will form between them, they will produce phenotypes similar to what they would if they were on different chromosomes. That is, 50% of the gametes will be of the parental type (non-recombinant) and 50% of the recombinant type. The frequency of recombination between two linked genes is constant and characteristic of that pair of genes. It cannot exceed 50%, even when there are multiple crossovers between them. The frequency of recombination increases the further apart these genes are, since the length of the chromosome fragment in which the crossover can occur is greater. Making a chromosome map If you know the crossover frequency between two genes, you can know the distance between them, and therefore the position (locus) that each gene occupies within the chromosome. The recombination unit (or map unit) is called centimorgan, and it is equivalent to the distance between two points on the chromosome, whose recombination frequency will be 1%. With the data of distances between the genes, chromosome maps can be made, which contain the genetic information of the species. Puzzle: Encuentra la Drosophila melanogaster. Licensed under the Creative Commons Attribution Share Alike License 4.0 « Previous \| Next » These pages are semi-automatically translated from the web Biology 2nd Baccalaureate. Biología de 2º de Bachillerato (biologia-geologia.com). You can make any suggestion, question, comment, ..., in our forum 2º Bachillerato Biología - Foro de biologia-geologia.com
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Ligation and recombination

Ligation

Recombination

Limits of recombination

Making a chromosome map