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Meiosis & Genetics

Meiosis & Genetics. Why can’t a sexual organism produce offspring through mitosis?. Meiosis. Chromosome and Chromosome Number Human body cells have 46 chromosomes Skin Muscle Each Parent contributes 23 chromosomes Homologous chromosomes 1 of 2 paired chromosomes, one from each parent.

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Meiosis & Genetics

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  1. Meiosis & Genetics

  2. Why can’t a sexual organism produce offspring through mitosis?

  3. Meiosis • Chromosome and Chromosome Number • Human body cells have 46 chromosomes • Skin • Muscle • Each Parent contributes 23 chromosomes • Homologous chromosomes 1 of 2 paired chromosomes, one from each parent

  4. Meiosis • Chromosome and Chromosome Number • Same length • Same centromere position • Carry genes that control the same inherited traits • To count chromosomes count centromeres

  5. Meiosis • The sexual life cycle in animals involves meiosis • Produces gametes • When gametes combine in fertilization, the number of chromosomes is restored

  6. Meiosis - Stages • Reduces chromosome number by ½ through separation of homologues • Two cell divisions • Meiosis I • Meiosis 2

  7. Meiosis • Consist of 2 Divisions • Produces 4 haploid cells that are not identical • Results in genetic variation

  8. Crossing Over • Takes Place in Prophase of Meiosis I • Crossing over produces exchange of genetic information • Crossing over- chromosomal segments are exchanged between a pair of homologous chromosomes

  9. Mitosis vs. Meiosis

  10. Types of Reproduction Asexual Sexual The organism inherits all of its chromosomes from a single parent The new individual is genetically identical to its parent • Beneficial genes multiply faster of time • Genetically diverse from its parents

  11. Mendelian Genetics • The passing of traits to the next generation is inheritance or heredity • Mendel- a monk who work with pea plants • Studied various traits in the peas

  12. P, F1, and F2 Generations • Parent generation - P generation • P x P - F1 generation or first filial generation • F1 x F1 - F2 generation or second filial generation

  13. Genes in Pairs • Allele- alternative form of a single gene • Dominant- able to mask • Recessive- can mask

  14. Dominance • Homozygous- two of the same alleles • Homozygous dominant (both dominant alleles) • Homozygous recessive (both recessive alleles) • Heterozygous- two different alleles • Genotype- an organisms pair of alleles • Phenotype- observable characteristic

  15. Mendel’s Law of Segregation • Two alleles separate during meiosis • You have a 50-50 chance of giving each allele

  16. Monohybrid Cross • Cross a homozygous dominant plant and with a homozygous recessive plant • tall - dominant • dwarf - recessive • What do we expect the F1 and F2 Generations to look like?

  17. Dihybrid Cross Dihybrid Cross Law of Independent Assortment Different chromosomes separate independently Genes on different chromosomes separate independently • Simultaneous inheritance of 2 traits in the same organism • Must be on different chromosomes

  18. Cross two pea plants that are each hybrid for height (Tt) and also hybrid for pod color • (T-Tall and t- dwarf) • (Y=yellow and y=green)

  19. What would happen? • What would happen if two genes were on the same chromosome? (Circle one) • A. They sort independently of each other • B. They don’t sort independently of each other • Why

  20. Albinism • Can affect only the eyes, skin, or hair or be complete

  21. Complex Inheritance and Human Heredity Sickle Cell Anemia • Autosomal Recessive • Red blood cells- sickle shape • heterozygotes have both normal and sickle-shaped cells • Heterozygotes protected from malaria • HH- no SCA/ get malaria • Hh- no SCA/ don’t get malari • hh- aflicted with SCA Sickle cell 7766x

  22. Pedigrees • A diagram that traces inheritance • Can be used to predict genetic disorders in families

  23. Incomplete Dominance • The heterozygote phenotype is a blend between the two homozygous phenotypes

  24. Codominance • Both alleles are expressed at the same time

  25. Complex Inheritance and Human Heredity Epistasis eebb eeB_ E_bb E_B_ Dark pigment present in fur No dark pigment present in fur One allele can hide the effects of another allele

  26. Sex Determination (mammals) • Sex Chromosomes • XX- female • XY- Male • Sex chromosomes determine gender

  27. Sex Linked Traits • Located on the X chromosome • Affects mostly males • Red Green Colorblindness • Hemophilia

  28. Polygenic Traits • Trait determined by many genes at many loci • Loci – locations on different chromosomes

  29. Explain The Twins

  30. Environmental Influences • Diet • Exercise • Sunlight and water • Temperature

  31. Look at you: nice work, human!

  32. Identical Twin Studies • Helps separate genetic contributions from environmental contributions • Traits that affect both twins are controlled partially by heredity • Traits expressed differently in identical twins are strongly influenced by the environment

  33. Karyotype Studies • Picture of the chomosomesaranged in decreasing size • Chromosomes are stained • Look for abnormalities • Number of chromosomes • Missing parts to chromosomes

  34. Nondisjunction • During meiosis- sister chromatids fail to separate properly • Down syndrome • Sex Chromosomes

  35. Down Syndrome Trisomy 21 47+21 Turners Syndrome 46 XO

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