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Genetics and Heredity

Genetics and Heredity. 9 Biology. Terminology. Chromosome Allele Homozygous Heterozygous Dominant Recessive Monohybrid Dihybrid. Incomplete dominance Gene Gamete XX, XY Phenotype Genotype Karyotype Mutation Autosomes. Chromosomes. Contain genetic information Made of DNA

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Genetics and Heredity

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  1. Genetics and Heredity 9 Biology

  2. Terminology • Chromosome • Allele • Homozygous • Heterozygous • Dominant • Recessive • Monohybrid • Dihybrid • Incomplete dominance • Gene • Gamete • XX, XY • Phenotype • Genotype • Karyotype • Mutation • Autosomes

  3. Chromosomes • Contain genetic information • Made of DNA • Humans have 23 pair • Undergo mitosis • Somatic cells, autosomes • Undergo meiosis • Gametes, sex cells, sperm and egg

  4. Genes • Encode for traits of an organism • Alternate form of a gene is an allele • You have 2 alleles for each trait • One from your mother • One from your father

  5. Alleles • Alleles can be dominant or recessive • Your genotype contains all the alleles that you carry • Your phenotype is the visible evidence of those alleles

  6. Example of Allele Dominance • Eye color: • Brown eyes are dominant over lighter colored eyes • In order for brown eyed parents to have a blue eyed child, they both must carry the recessive allele for blue eyes

  7. Dominant vs. Recessive • Dominant alleles are expressed in the organism’s phenotype • (visible) • Recessive alleles are only expressed if the organism has 2 copies of the recessive allele

  8. Incomplete Dominance • Incomplete dominance results in an intermediate phenotype • Ex: Red flowers and white flowers • When red and white flowers are crossed, their offspring are pink

  9. Mendelian Genetics and Monohybrid Crosses • GregorMendel • Monk who experimented with crosses of pea plants • Considered the “Father of Genetics” • Worked out genetic probabilities using Punnett squares • Worked with monohybrid and dihybrid crosses

  10. Homozygous and Heterozygous • Homozygous: • Both alleles are the same • Ex: AA or aa • AA indicates the dominant allele is expressed in phenotype • aa indicates the recessive allele will be expressed in phenotype • Heterozygous: • Both of the alleles are different • Ex: Aa • Aa indicates the dominant allele will be expressed in phenotype, but the individual is a carrier of the recessive allele

  11. Monohybrid Crosses Using Punnett Squares • Crosses that involve one trait • Assign letters indicating dominant and recessive alleles • Ex: B (dominant purple) • b (recessive white) • Female genotype Bb • Male genotype Bb

  12. Monohybrid Crosses Using Punnett Squares, cont. • Results: • Offspring genotypes: • BB, Bb, Bb, bb • Offspring phenotypes: • 3 purple petals • 1 white petals • Homozygous: • 2 alleles that are the same (BB or bb) • Heterozygous: • 2 alleles that are not the same ( Bb)

  13. Monohybrid Practice:

  14. Ratios and Percentages • Interpretation of genetic crosses often require either a ratio or a percentage. • Genotypic ratio: • 1:2:1 (1 BB, 2Bb, 1 bb) • Phenotypic ratio: • 3:1 (3 purple, 1 white) • Genotypic percentage: • 25% BB, 50% Bb, 25% bb • Phenotypic percentage: • 75% purple, 25% white

  15. Dihybrid Crosses • Dihybrid crosses use 2 traits • They also use Punnett squares, but have 16 squares instead of 4 • Example: Seed color/ seed texture • Parent 1 RrYy • Parent 2 RrYy • Phenotype for both: yellow, smooth

  16. Setting Up Dihybrid Crosses • 1. Identify genotype of the parents. • RrYy and RrYy • Write: • 1 2 3 4 & 1 2 3 4 • R r Y y & R r Y y • Use this series of pairings to label your dihybrid Punnett square: • 1-3, 1-4, 2-3, 2-4 • 1-3= RY 1-3= RY • 1-4= Ry 1-4= Ry • 2-3= rY 2-3= rY • 2-4= ry 2-4= ry

  17. Interpreting Dihybrid Crosses • Genotypes: • RRYY ( 1 ) • RRYy ( 2 ) • RrYY ( 2 ) • RrYy ( 4 ) • Rryy ( 3 ) • rrYY ( 3 ) • rryy ( 1 )

  18. Interpreting Dihybrid Crosses, cont. • Phenotypes: • Yellow, round = 9 • Green, round = 3 • Yellow, wrinkled = 3 • Green, wrinkled = 1 • Phenotypic ratio: • 9:3:3:1 • Classic ratio for the dihybrid cross of 2 heterozygotes

  19. Practice!

  20. XX and XY • Females are genetically XX • Female egg carries only X chromosomes • Males are genetically XY • Male sperm carries both X and Y chromosomes • Male sperm determines the sex of the baby • The sex chromosomes are the last pair of chromosomes in a karyotype. • The X chromosome is quite large, and the Y chromosome is quite small

  21. X and Y Chromosomes

  22. Karyotypes • Karyotypes are photographs of chromosomes • Chromosomes are matched by hand or computer, in pairs depending on their size, and centromere placement • Karyotypes can tell us: • If the number of chromosomes is normal • If the fetus will have a genetic defect of chromosome number • Karyotypes cannot tell us: • the degree of limitations the fetus may have

  23. Sex-Linked Disorders • Carried only on X chromosome • Because of incomplete masking of the X chromosome by the Y, males are more frequently affected. • Examples of Sex-Linked Disorders: • Color-blindness • Hemophilia • Duchenne's Muscular Dystrophy

  24. Co-Dominance • Co-dominance occurs when neither allele is dominant • Both alleles are expressed • Example: • Blood Typing • There are 4 blood types: • A, AB, B, O • The alleles are: • IA, IB, i Combinations are: IAIA, IAi, IAIB, IBIB, IBi, ii Blood types are either Rh+ or Rh– Rhesus factor: a protein that is either present, or not present

  25. https://www.youtube.com/watch?v=xfZhb6lmxjk

  26. Practice Blood Type Crosses

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