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This review covers the foundational concepts of Mendelian genetics, highlighting Gregor Mendel, the pioneering figure known as "the father of genetics." Utilizing pea plants for experimentation, Mendel elucidated concepts such as dominant and recessive alleles, gamete formation, and inheritance patterns through his laws. The guide explains monohybrid and dihybrid crosses using Punnett squares, illustrating genotypic and phenotypic ratios. Key terms like homozygous, heterozygous, and true-breeding are defined to enhance understanding of genetic probabilities and trait inheritance.
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Gregor Mendel- “the father of genetics” • Used pea plants because of their relative simplicity and short reproductive cycle. • Why do certain traits disappear in one generation and reappear in the next? • “elementen”
Mendel’s Laws • Paired genes will separate from one another during gamete formation • As long as genes are not linked, that is they are found on separate chromosomes, the inheritance of one gene will not guarantee the inheritance of another.
Dominant vs. recessive alleles • 1 initial for a gene • Capital domiant, lowercase recessive • P, F1, F2 generations • True-breeding
Diploid organisms have 2 sets of chromosomes- one maternal, one paternal • 2 alleles for every trait
Monohybrid Punnett Square Letters on the outside represent possible alleles in the gametes (haploid) Letters in the boxes represent possible gene combinations of individuals in a new generation (diploid)
Genotype- • Phenotype- • Pay attention for what is being asked for and do not give the opposite! • 3 possibilities for genotype: • Homozygous dominant, Heterozygous, Homozygous recessive
Wildtype vs. Mutant • Know how these terms relate to Punnett square problems. Can you use this information in your Punnett square?
Dihybrid Crosses • Looking at two traits simultaneously
Dihybrid steps to success! • Identify the genotypes of the parents • Identify the possible allele combinations in the gametes for each parent separately • Line up possible gametes along the punnett square. • Cross individuals You may not need to use all 16 squares!!
Example: • Parent 1: CCdd- gamete possibilities: Cd • Parent 2: CcDD- gamete possibilities: CD, cD • Cross: Cd CD cD
Ratios • Separate with colon ( : ) • Genotypic is a ratio of GENOTYPES • Common genotypic ratios for monohybrid crosses • 1:2:1 • 1:1 • 1
Ratios • Phenotypic is a ratio of PHENOTYPES • Common phenotypic ratios for monohybrid cross: • 3:1 • 1:1 • 1 Phenotypic ratio when heterozygous for all traits in a dihybrid cross: - 9:3:3:1 (Dom/Dom, Dom/Rec, Rec/Dom, Rec/Rec)
Probability • Expected/Total • Give as a fraction, decimal, or percent. • Two heterozygous purple flowers are crossed. What is the probability of having a white flower in their F1 generation? • ¼, or 0.25, or 25%
Product Rule • When dealing with more than one trait: • The probability of inheriting a combination of traits is the same as the product of the probability of inheriting each trait individually. Parent 1: AABbCc Parent 2: AaBbcc What is the probability of having an offspring that is heterozygous for all traits? AaBbCc ½ * ½ * ½ = 1/8
Vocabulary • Dominant • Recessive • Allele • Genotype • Phenotype • Homozygous • Heterozygous • True-breeding • Wildtype • Mutant • Gene • “Elementen” • P,F1,F2 generations • Genotypic ratio • Phenotypic ratio
