Patterns of Inheritance – Mendelian Genetics
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Transcript of Patterns of Inheritance – Mendelian Genetics
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
Self-fertilization Pea flowers can self-fertilize
Pollen from male structures transfers to eggs in female structures
True-breeding
Plants homozygous for a characteristic are true-breeding
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
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
Genetic Cross
The mating of pollen and eggs (from same or different parents)
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.
Alleles
Every cell in a pea plant carries 2 alleles per characteristic (either the same or different)
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)
Dominant and Recessive Alleles
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
How Meiosis Separates Genes
Separation of alleles in meiosis is known as Mendel’s Law of Segregation
Genetic Bookkeeping Punnett Square Method predicts offspring
genotypes from combinations of parental gametes
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
The Test Cross
Traits Inherited Independently
Mendel performed genetic crosses in which he followed the inheritance of two traits at the same time
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)
Traits Inherited Independently
2 trait cross was between two true breeding varieties for each characteristic
P: SSYY x ssyy
Traits Inherited Independently
Mendel then allowed the F1 offspring to self fertilize: SsYy x SsYy
Mendel’s Genius Went Unrecognized