9.2.2.1. Mendel's first law or principle of uniformity in the first generation

Mendel's First Law

All hybrid offspring resulting from the cross between two homozygous individuals are equal to each other.

When two pure races are crossed (a dominant homozygous with a recessive one) for a certain trait, all the descendants of the first generation (F₁) will be equal to each other, phenotypically and genotypically, and phenotypically equal to one of the parents (genotype dominant), regardless of the direction of the cross. The corresponding character is called dominant (A = yellow), and recessive (a = green) which is masked.

A = Yellow seed; a = green seed. A > a

That is:

P AA * aa or aa * AA

F ₁All Aa

F ₁ 100% All yellow seeds.

By Miguelferig (Own work) [CC0], via Wikimedia Commons

Review: Mendel's First Law (4th ESO).

Genetics problems solved: Practice with exercises in genetics of Mendel's first law (4th ESO).

Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU)

Genetics problems solved: Practice with exercises in genetics of Mendel's first law (4th ESO). It contains genetic problems that have come out in EvAU exams from several Universities.

Madrid, July 2019, option A, question 1

Regarding Mendel's contributions to the study of heredity:

a) State Mendel's First Law. Explain what the genotype of the parents is like if, in an experimental cross between pea plants, it is observed that a recessive trait "a" is manifested in all the offspring (0.5 points).

b) Explain the different manifestation of a recessive character linked to the X chromosome in a man and in a woman, and cite an example (0.75 points).

c) Relate each concept in the left column with a definition in the right column (0.75 points).

1. Intermediate inheritance A. Identical alleles for the same locus
2. Linked genes B. Diagram of the genetics of several generations of a family
3. Pedigree C. Inherited alleles for a gene
4. Homozygous D. Representation of the possible offspring of a cross
5. Punnett square E. They are on the same chromosome
6. Genotype F. Phenotype mixture of two purebreds

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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. 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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 » 9.2.2.1. Mendel's first law or principle of uniformity in the first generation Mendel's First Law All hybrid offspring resulting from the cross between two homozygous individuals are equal to each other. When two pure races are crossed (a dominant homozygous with a recessive one) for a certain trait, all the descendants of the first generation (F₁) will be equal to each other, phenotypically and genotypically, and phenotypically equal to one of the parents (genotype dominant), regardless of the direction of the cross. The corresponding character is called dominant (A = yellow), and recessive (a = green) which is masked. A = Yellow seed; a = green seed. A > a That is: P AA * aa or aa * AA F ₁All Aa F ₁ 100% All yellow seeds. By Miguelferig (Own work) [CC0], via Wikimedia Commons Review: Mendel's First Law (4th ESO). Genetics problems solved: Practice with exercises in genetics of Mendel's first law (4th ESO). Questions that have come out in University entrance exams (Selectividad, EBAU, EvAU) Genetics problems solved: Practice with exercises in genetics of Mendel's first law (4th ESO). It contains genetic problems that have come out in EvAU exams from several Universities. Madrid, July 2019, option A, question 1 Regarding Mendel's contributions to the study of heredity: a) State Mendel's First Law. Explain what the genotype of the parents is like if, in an experimental cross between pea plants, it is observed that a recessive trait "a" is manifested in all the offspring (0.5 points). b) Explain the different manifestation of a recessive character linked to the X chromosome in a man and in a woman, and cite an example (0.75 points). c) Relate each concept in the left column with a definition in the right column (0.75 points). 1. Intermediate inheritance A. Identical alleles for the same locus 2. Linked genes B. Diagram of the genetics of several generations of a family 3. Pedigree C. Inherited alleles for a gene 4. Homozygous D. Representation of the possible offspring of a cross 5. Punnett square E. They are on the same chromosome 6. Genotype F. Phenotype mixture of two purebreds 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. 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Mendel's First Law