patterns of inheritance – mendelian genetics
DESCRIPTION
Patterns of Inheritance – Mendelian Genetics. Genes. Location of a gene on a chromosome is called its locus Homologous chromosomes. What are alleles?. Homozygous Alleles vs. Heterozygous Alleles. Who Was Gregor Mendel?. nitro.biosci.arizona.edu. Secrets of Mendel’s Success. - PowerPoint PPT PresentationTRANSCRIPT
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Patterns of Inheritance – Mendelian Genetics
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Genes
Location of a gene on a chromosome is called its locus
Homologous chromosomes
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What are alleles?
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Homozygous Alleles vs. Heterozygous Alleles
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Who Was Gregor Mendel?
nitro.biosci.arizona.edu
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Secrets of Mendel’s Success
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Self-fertilization Pea flowers can self-fertilize
Pollen from male structures transfers to eggs in female structures
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True-breeding
Plants homozygous for a characteristic are true-breeding
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Cross-fertilization
Mendel was able to mate two different plants by hand (cross-fertilization)
Female parts (carpels) were dusted with pollen from other selected plants
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Secrets of Mendel’s Success
Mendel experimental design was simple and methodical
Chose a good organism to study
Studied characteristics that have unmistakably different forms (like purple versus white)
Studied one trait (characteristic) at a time
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Genetic Cross
The mating of pollen and eggs (from same or different parents)
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Genetic Cross Parents used in a cross are part of the
parental generation (known as P)
Offspring of the P generation are members of the first filial generation (F1)
Offspring of the F1 generation are members of the F2 generation, etc.
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Alleles
Every cell in a pea plant carries 2 alleles per characteristic (either the same or different)
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Genotype vs Phenotype
Genotype Particular combination of the 2 alleles carried
by an individual (e.g. PP, Pp, or pp)
Phenotype Physical expression of the genotype
(e.g. purple or white flowers)
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Dominant and Recessive Alleles
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How Meiosis Separates Genes
2 alleles for a characteristic separate during gamete formation (meiosis)
Homologous chromosomes separate in meiosis anaphase I
During meiosis anaphase II, each gamete receives one of each pair of homologous chromosomes and thus one of the two alleles per characteristic
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How Meiosis Separates Genes
Separation of alleles in meiosis is known as Mendel’s Law of Segregation
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Genetic Bookkeeping Punnett Square Method predicts offspring
genotypes from combinations of parental gametes
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Genetic Bookkeeping From the sums of all the different kinds of
offspring genotypes, create a genotypic ratio ¼ PP, ½ Pp, ¼ pp is in the ratio 1PP: 2Pp:
1pp
Based on dominant and recessive rules, determine the phenotypic ratio A genotypic ratio of 1PP: 2Pp: 1pp yields 3 purple flower plants: 1 white flower
plant
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The Test Cross
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Traits Inherited Independently
Mendel performed genetic crosses in which he followed the inheritance of two traits at the same time
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Traits Inherited Independently
Seed color (yellow vs. green peas) and seed shape (smooth vs. wrinkled peas) were characteristics studied
Allele symbols were assigned: Y = yellow (dominant), y = green (recessive) S = smooth (dominant), s = wrinkled (recessive)
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Traits Inherited Independently
2 trait cross was between two true breeding varieties for each characteristic
P: SSYY x ssyy
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Traits Inherited Independently
Mendel then allowed the F1 offspring to self fertilize: SsYy x SsYy
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Mendel’s Genius Went Unrecognized