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NoteStudied by 6 peopleGenetics Notes
- Mendel used the scientific approach to identify two laws of inheritance
- Mendel’s Experimental, Quantitative Approach
- Character: a heritable feature that varies among individuals (i.e. hair color)
- Trait: variants of character (i.e. red, black or blonde)
- Peas were good because they were simple, had clear variation, a short generation time and produced many offspring
- Mendel used true-breeding parents (they produced the same trait over many generations) and controlled flower fertilization
- Mendel crossed for many generations and used large sample sizes
- The Law of Segregation
- Disproved the blending theory as traits reappeared after not being expressed in one generation
- Mendel’s Model
- Alternative versions of genes account for variations in inherited characters. Alleles arise from slight differences in the nucleotide sequences at a locus.
- For each character, an organism inherits two copies of a gene, one from each parent.
- If two alleles at a locus differ, then one, the dominant allele, determines the appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance.
- Law of Segregation: Two alleles from gametogenesis separate into different gametes.
- The Test-Cross
- The test-cross is used to determine if an organism is heterozygous or homozygous dominant for a particular trait, cross the organism with another organism which is homozygous recessive.
- If there is a 1:1 ratio of dominant to recessive phenotypes, then the unknown organism is heterozygous
- If there is a 1:0 ratio of dominant to recessive phenotypes, then the unknown organism is homozygous dominant
- The Law of Independent Assortment
- Monohybrid: organisms that are heterozygous for ONE trait
- Dihybrid: organisms that are heterozygous for TWO traits
- Alleles for one gene assort independently. Only applies to genes on that are on different chromosomes or are far apart on a single chromosome.
- 14.2: Probability laws govern Mendelian inheritance
- Multiplication and Addition Rules
- Multiply probabilities for one or more independent affairs
- Add probabilities for two or more mutually exclusive wheels
- 14.3: Inheritance patterns are often more complex than predicted by simple Mendelian genetics
- Extending Mendelian Genetics for a Single Gene: Simple Mendelian genetics do not apply when there is incomplete dominance/recession, polygenic traits or when a single gene controls multiple phenotypes
- Degrees of Dominance
- Incomplete Dominance: Neither allele is completely dominant nor recessive
- Codominance: This is where both alleles are EQUALLY EXPRESSED
- The Relationship Between Dominance and Phenotype
- Dominant and recessive allele plays into effect solely from genotype to phenotype
- Frequency of Dominant Alleles
- Dominant alleles are not inherently more common than recessive alleles or vice versa
- Multiple Alleles
- Most genes exist in more than two allelic forms
- For example, blood type (IA, IB and i)
- Pleiotropy
- Most genes have multiple phenotypic effects
- For example, in peas, the gene for flower color also controls the color of the seed coating
- Extending Mendelian Genetics for Two or More Genes
- Epistasis: one gene affects another because the gene products are related
- Polygenic Inheritance: multiple genes independently affect a single trait
- Quantitative Characters: traits that are not A or B, rather they exist as a gradient
- For example, skin color and hair color.
- Genotypes are most commonly associated with a range of phenotypes, not typically a single phenotype
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Explore Top NotesNoteStudied by 4 peopleNoteStudied by 186 peopleNoteStudied by 5 peopleNoteStudied by 8 peopleNoteStudied by 38 peopleNoteStudied by 6 people
Thinking Scientifically - Skills Of Scientific Investigation (copy)
NoteStudied by 4 peopleChapter 1 - The Collision of Cultures
NoteStudied by 186 peopleHello
NoteStudied by 5 peopleHistory of England
NoteStudied by 8 peopleChapter 1 - The Earth (copy)
NoteStudied by 38 peopleEssay
NoteStudied by 6 people