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Understanding Mendel's Experiments and Genetic Principles in Human Genetics

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This summary explores Gregor Mendel’s groundbreaking experiments on inheritance, particularly his dihybrid crosses illustrating the principle of independent assortment. Mendel’s work showed that alleles for different traits segregate independently during gamete formation, a key factor contributing to genetic diversity. The text also discusses exceptions to Mendelian principles, such as incomplete dominance and codominance, as seen in flower colors and human blood types. Furthermore, it highlights the importance of karyotypes and pedigrees in diagnosing genetic disorders and understanding hereditary relationships, alongside the interplay between genes and environmental factors.

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Understanding Mendel's Experiments and Genetic Principles in Human Genetics

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  1. Different Genetic Outcomes and Human Genetics Chapters 11.3 and 14.1

  2. Mendel’s experiments further • In his first experiment Mendel showed that the alleles for a trait segregated independently • Now he wondered if alleles for different traits were linked • He conducted a dihybrid cross  two traits • Crossed a true-breeding yellow round seed plant (RRYY) with a true-breeding green wrinkled seed plant (rryy) • F1 generation was 100% yellow and round • You can see this result with a 16 box punnett square • He then crossed the F1 offspring • 9 yellow round • 3 yellow wrinkled • 3 green round • 1 green wrinkled • This led to Mendel’s principle of independent assortment • Genes for traits segregate independently from each other during the formation of gametes in meiosis • This accounts for the wide variety of genetic variation in organisms

  3. Exceptions to Mendel’s principles • Incomplete dominance  When one allele is not completely dominant over another • Crossing a red flower and a white flower and the offspring are pink • Codominance two genes are dominant and show • Cross a black chicken with a white chicken and the offspring are black and white • Blood types in humans • A and B are dominant, O is recessive

  4. Human Genetics • Karyotype a picture of all the chromosomes • Can be used to diagnose genetic disorders • Humans have 46 chromosomes or 23 pairs • The first 22 pairs are called autosomes, the last pair are the sex chromosomes • Females have two X chromosomes • Males have an X and a Y

  5. Pedigrees  a tool used to show relationships within a family • Genetic counselors analyze pedigrees to determine possible genotypes of family members • Can be used to predict genetic diseases • Genes and environment  a phenotype is only partially determined by genes, the environment plays a role as well • Ex: height is genetically determined but can be affected by poor nutrition

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