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Understanding Genetics: Meiosis, Mendel, and Punnett Squares

This comprehensive overview of genetics explores critical concepts such as meiosis, the formation of haploid sex cells, and the significance of dominant and recessive alleles. Dive into Gregor Mendel's pioneering work with pea plants, illustrating how traits are passed down through generations via alleles. Learn the definitions of key terms including genotype and phenotype, and how Punnett squares are utilized to predict offspring outcomes. This resource is perfect for students looking to grasp the fundamentals of genetic inheritance.

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Understanding Genetics: Meiosis, Mendel, and Punnett Squares

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  1. Genetics Review Bell Ringer: Copy All of Agenda (Leave it out so I can see!)

  2. Meiosis • Remember that meiosis creates 4 different sex cells (sperm or egg) • These sex cells are HAPLOID so they have half the number of chromosomes • Thanks to INDEPENDENT ASSORTMENT we are never sure which allele is going to end up in the sex cell

  3. Fertilization • When two sex cells come together they form a DIPLOID zygote • This zygote is a combination of the mother and father’s alleles. • Thus, everyone has TWO alleles for any gene

  4. Mendel • Gregor Mendel was the “father of genetics” • He studied pea plants and determined that the way they looked was due to unseen “factors” • We now know that these factors he was • referring to were genes

  5. Genes & alleles • Any TRAIT (characteristic about you) is determined by your GENES. • GENES are regions of your DNA. Genes come in different kinds. • ALLELES are different versions of the same gene. For example, there might be a gene for hair color and the alleles can be black, blonde or brown.

  6. Alleles • For simple traits, there are dominant and recessive alleles • DOMAINANT alleles always mask the recessive ones • The only way for recessive traits to show up is if they are the only alleles present.

  7. Genotype & Phenotype • GENOTYPE is the actual alleles someone gets (Example: AA or aa) • PHENOTYPE is how those alleles appear in the organism (Example: blonde hair, blue eyes, attached earlobes)

  8. HETEROZYGOUS VS. HOMOzYGOUS • HETEROZYGOUS means an individual had two different alleles (one dominant, one recessive) • HOMOZYGOUS means that an individual has two of the same allele (AA or aa, both dominant or both recessive)

  9. ALLELEs • What is the genotype of a person who is heterozygous for Hitchhiker’s thumb (H) • Having a straight thumb is recessive. What is the genotype of someone

  10. Punnett Squares • When we want to know the outcome of a particular cross (two parents breeding), we can use a punnett square. • PUNNETT SQUARES are ways to predict the potential offspring

  11. Punnett squares • Punnett squares model what would happen if two organisms had offspring. Since we don’t know what alleles a mom or dad will give we show all 4 possibilities. • We put the parent’s alleles along the • sides and top. Then we fill in the • boxes so each child has 2 • alleles.

  12. Punnett Squares • What is wrong with the following punnett square?

  13. Vocab Words • Morphemes are the smallest unit of meaningful language • The following at the vocab words for you to define: • Homozygous • Heterozygous • Genotype • Phenotype • Haploid • Diploid

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