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Genetic traits…which do you have?

Genetic traits…which do you have?. Widows peak vs. straight hairline Free earlobes vs. attached earlobes Dimples vs. no dimples Cleft chin vs. no cleft chin Straight thumb vs. curved thumb Mid-digit hair vs. no mid-digit hair Longer 2 nd toe vs. shorter 2 nd toe (compared to big toe)

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Genetic traits…which do you have?

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  1. Genetic traits…which do you have? • Widows peak vs. straight hairline • Free earlobes vs. attached earlobes • Dimples vs. no dimples • Cleft chin vs. no cleft chin • Straight thumb vs. curved thumb • Mid-digit hair vs. no mid-digit hair • Longer 2nd toe vs. shorter 2nd toe (compared to big toe) • Can roll tongue vs. can’t roll tongue

  2. Chapter 11 Introduction to Genetics

  3. 11-1 the work of gregormendel • Heredity: transmitting genetic information from parent to offspring • Genetics: the study of heredity • Gene: a piece of DNA that codes for a trait • Alleles: a different form of a gene • Trait: specific characteristic that varies between individuals • Gametes: specialized cells involved in sexual reproduction (eggs and sperm)

  4. Mendel and his peas • A priest with a garden… • Studied pea plants • Male part = stamen • Female part = pistil • Fertilization: joining of male and female parts • Form a new cell (seed)

  5. Pea plants = true breeding • True-breeding: pass on ALL genetic traits to offspring • Self-pollinating- use male and female parts from same plant • Breed offspring identical to parent

  6. Cross-breeding • Using male and female parts from different plants • Mendel attempted this with pea plants • Aka: cross pollination

  7. So what did mendel do? • Identified 7 traits • each with 2 contrasting characteristics • Crossed those characteristics • Resulted in hybrid plants • P generation (parents) • F1 generation (offspring)

  8. What did he find? • Offspring only showed the traits of one parent • 2 conclusions: • 1. Inheritance is determined by factors passed from parent to offspring (genes and alleles) • 2. Principle of dominance • some alleles are dominant others recessive

  9. Where did the recessive trait go? • Next, Mendel allowed self pollination to occur again • Results of F2 generation (offspring’s offspring)… • ¾ of the plants = showed dominant trait • ¼ of plants = showed recessive trait • The recessive trait was still there…just “hiding”

  10. segregation • Separation of alleles during gamete formation • Occurs so gametes only carry one type of allele • Why we saw only one type of the trait II I Mom gametes I II Dad

  11. 11-2 probability and punnett squares • Mendel repeated experiments, got same results • Probability: likelihood that an event will occur • Ex: coin flip (1 in 2 odds) • Each turn is independent of any previous or future turns • Principles of probability can be used to predict outcomes of genetic crosses

  12. Punnett squares • Used to predict/compare the genetic variations that will result from a cross • Alleles: • capital letter = dominant • lowercase letter = recessive

  13. Punnett squares (Tt) Parent’s alleles The boxes in the square contains every possible combination of alleles (Tt)

  14. Punnett squares • TT or tt = homozygous (2 identical alleles) • Tt = heterozygous (2 different alleles) • TT or Tt = dominant allele will show • tt = recessive allele will show • ¾ = dominant allele shown • ¼ = recessive allele shown • *3:1 ratio for dominant trait

  15. Genotype vs. phenotype • Genotype:genetic makeup • What the alleles are (TT, Tt or tt) • Phenotype:physical characteristics • What you see (tall or short) TT or Tt tt

  16. Probability and predictions • REMEMBER: probability only predicts averages • NOT precise outcomes • Larger numbers of trials means outcomes closer to the probability

  17. Punnett square example questions • In seals, whisker length is determined by two alleles. “W” codes for long whiskers and is dominant over “w” which codes for short whiskers. Draw a Punnett square to show a cross between a homozygous long whiskered dad and a heterozygous long whiskered mom. • What percentage of their offspring would have long whiskers? Short whiskers? • What percentage of their offspring would be homozygous? What percentage would be heterozygous?

  18. Punnett square example answers • What percentage of their offspring would have long whiskers? • 100% • What percentage would have short whiskers? • 0% • What percentage of their offspring would be homozygous? • 50% • What percentage would be heterozygous? • 50%

  19. 11-3 exploring meNdelian genetics • Mendel’s next question: do alleles separate independently? • Tried crossing 2 traits at once • Found that round (R) peas and yellow (Y) peas were dominant traits • Would they stay together or separate?

  20. Law of independent assortment • Genes for different traits will segregate independently of each other during gamete formation • Accounts for all genetic variation!

  21. Summary of mendel’s principles • Inheritance of traits is determined by genes (alleles) passed from parent to offspring • When 2 or more alleles exist, some will be dominant and some will be recessive • In sexually reproducing organisms, each adult has 2 copies of each gene which separate when gametes are formed • Alleles for different traits usually separate independently

  22. Exceptions to the rules • Genetics is very complicated • Some alleles are not simply dominant/recessive • Some traits controlled by multiple genes

  23. Incomplete dominance • One allele is not completely dominant over another • A “mixing” occurs • Ex: Mirabilis plant- crossing red flowers with white flowers gives you pink flowers X

  24. codominance • 2 dominant alleles (both will contribute to the phenotype) • Both alleles are present and can be “seen” • Ex: erminette chicken- has both black and white feathers

  25. Multiple alleles • 3 or more alleles available • Gives more options for the combination of alleles • Ex: blood types

  26. Polygenic traits • Traits controlled by 2 or more genes • Ex: skin color • LOTS of variation

  27. Applying mendel’s principles • Thomas Hunt Morgan • Used fruit flies • All principles held true

  28. Genetics and the environment • Genes act as the “blue print” plan for living things • Environment will influence how the plan works • Ex: sunflower • Height and color determined by genes • Influenced by water, light, temperature, soil, etc.)

  29. 11-4 Meiosis • Mendel’s principles require 2 things: • 1. Organisms inherit single copy of genes from each parent • 2. Therefore, when gametes are formed, those copies must separate • But…how?

  30. chromosomes • Remember: genes are found on chromosomes • Half come from mom and half come from dad • Each chromosome has a “corresponding chromosome” • (1 from mom and 1 from dad) • Known as homologous chromosomes

  31. Chromosomes • Diploid- cells that contain both sets of homologous chromosomes • Haploid- cells that contain only a single set of homologous chromosomes • Gametes!

  32. mEIosis • Meiosis: the process where chromosome # is cut in half by separating homologous chromosomes in diploid cells (makes gametes) • Turns 1 diploid cell into 4 haploid cells • Involves meiosis I and meiosis II

  33. Meiosis I • Must go thru interphase first to replicate chromosomes • Prophase I- chromosomes pair with homologous chromosomes (these are called tetrads) • Crossing over- exchange parts of chromatids • Very important for genetic variation • Get new allele combinations

  34. Meiosis 1 (continued) • Metaphase I- line up across middle, attach to spindle • Anaphase I- spindle pulls homologous chromosomes apart • TelophaseI- two new nuclear membranes form • Cytokinesis- two new diploid cells are formed

  35. Important! • After Meiosis 1, the 2 new diploid cells have “shuffled” sets of chromosomes • From “crossing over” • Different from each other • Different from original cell • Genetic variation

  36. Meiosis II • Prophase II- sister chromatids condense • Metaphase II- sister chromatids line up • Anaphase II- sister chromatids separate • Telophase II and cytokinesis = 4 new haploid cells

  37. Gamete formation • Males = sperm • Females = eggs • usually, only 1 of the 4 produced are used in reproduction (actually become an egg)

  38. Mitosis vs. meiosis • Mitosis • End with 2 genetically identical diploid cells • Role: growth and replacement of cells • Asexual reproduction • Meiosis • End with 4 genetically different haploid cells • Role: make gametes

  39. 11-5 linkage and gene maps • Linkage: if genes are close to each other on a chromosome, they may be inherited “linked” together • chromosomes follow the Law of Independent Assortment…NOT individual genes

  40. Gene maps • Gene maps:shows the relative locations of genes on a chromosome • How can we tell this? • The closer together genes are, the more likely they are to be “linked” • Human Genome Project

  41. Annemarie parisi… • Will you go to prom with me? • -EJ

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