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Understanding Meiosis and Mendelian Genetics: Gametes, Inheritance, and Ratios

This comprehensive overview details the process of meiosis, highlighting how it produces four haploid gametes with unique genetic configurations distinct from the original cell. It outlines key concepts including independent assortment, crossing over, and Mendelian ratios in monohybrid and dihybrid crosses. The genetic makeup of gametes from different parental genotypes is analyzed using Punnett squares, demonstrating the principles of inheritance for traits such as color and shape in a simplified manner. Discover how gamete combinations lead to varied offspring outcomes in genetic studies.

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Understanding Meiosis and Mendelian Genetics: Gametes, Inheritance, and Ratios

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  1. Genetics & Heredity

  2. Meiosis • Resulting cells have a different genetic configuration than the original cell. • End product is 4 haploid gametes • 2 divisions occur, not 1 • Crossing over may occur • 1 replication with 2 divisions

  3. Independent assortment • Genes on different chromosomes behave independently during meiosis. • Separate chromosomes will separate into gametes independently of each other.

  4. Meiosis parents Tt Tt T T t t gametes T T t t Male gametes Female gametes

  5. Punnet Squares Tt x Tt= genotype T t T t= gametes

  6. Punnet Squares Tt x Tt= genotype T t x T t= gametes Male gametes t T

  7. Punnet Squares-monohybrid cross Male gametes Tt x Tt= genotype T t x T t= gametes t T T Female Gametes t

  8. Punnet Squares-monohybrid cross Male gametes Tt x Tt= genotype T t x T t= gametes t T T TT Female Gametes t

  9. Punnet Squares-monohybrid cross Tt x Tt= genotype T t x T t= gametes Male gametes T t T TT Tt Female Gametes t

  10. Punnet Squares-monohybrid cross Tt x Tt= genotype T t x T t= gametes Male gametes t T T TT Tt Female Gametes t tT

  11. Punnet Squares-monohybrid cross Tt x Tt= genotype T t x T t= gametes Male gametes t T T TT Tt Female Gametes t tT tt

  12. Punnet Squares-monohybrid cross Tt x Tt= genotype T t x T t= gametes Male gametes t T T TT Tt Female Gametes t tT tt Mendelian Ratios: Genotypic: 1TT: 2 Tt: 1tt Phenotypic: 3 dominant: 1 recessive

  13. Chromosomes and Sex Determination • Human sperm contains 23 chromosomes, 22 of which are autosomes and 1 which is the sex chromosome. Half the sperm have an “X” sex chromosome, the other 1/2 has a “Y” sex chromosome. • The ovum also contains 22 autosomes and 1 sex chromosome; it’s sex chromosome has been designated “X”. • XX zygote= female : XY zygote= male

  14. Gamete combination possibilities • In a situation with Green (yy) and Round (RR) versus yellow (YY) and wrinkled (rr) • gametes would be yy X RR or 4 yR • 4 Yr Heterozygotes for these traits would be • Rr X Yy and the four gametes would be: • YR Yr yR yr

  15. Dihybrid Cross Genotypes: RrYy x RrYy Gametes: What are the gametes

  16. Dihybrid Cross Genotypes: RrYy x RrYy Gametes: RY Ry rY ry RY Ry rY ry

  17. Dihybrid Cross Genotypes: RrYy x RrYy Gametes: RY Ry rY ry RY Ry rY ry Ry RY rY ry RY Ry rY ry

  18. Dihybrid Cross Genotypes: RrYy x RrYy Gametes: RY Ry rY ry RY Ry rY ry Ry RY rY ry RRYY RRYy RY Ry rY ry

  19. Dihybrid Cross Genotypes: RrYy x RrYy Gametes: RY Ry rY ry RY Ry rY ry Ry RY rY ry RRYY RRYy RrYY RrYy RY RRYy RRyy RrYy Rryy Ry RrYY RrYy rrYY rrYy rY RrYy Rryy rrYy rryy ry

  20. Ry RY rY ry RRYY RRYy RrYY RrYy RY RRYy RRyy RrYy Rryy Ry RrYY RrYy rrYY rrYy rY RrYy Rryy rrYy rryy ry Dihybrid Cross Genotypes: RrYy x RrYy Gametes: RY Ry rY ry RY Ry rY ry Mendelian Ratios: R-Y- 9/16 rrY- 3/16 R-yy- 3/16 rryy- 1/16

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