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Meiosis: 10 th Grade

Meiosis: 10 th Grade. Resources. Homework for Monday. Create a document which outlines the process of meiosis Your document must be accurate, must demonstrate knowledge, and must be creative Label AT LEAST: gene; chromosome; DNA, crossing over and all the steps of meiosis.

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Meiosis: 10 th Grade

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  1. Meiosis: 10th Grade

  2. Resources

  3. Homework for Monday Create a document which outlines the process of meiosis Your document must be accurate, must demonstrate knowledge, and must be creative • Label AT LEAST: gene; chromosome; DNA, crossing over and all the steps of meiosis

  4. What is the biological purpose of sex?

  5. Meiosis is a two step process • Meiosis 1 separates the homologous pairs of chromosomes: this is the reduction division • Meiosis 2 separates the sister chromatids (resembles mitosis) • One single diploid cell produces 4 non-identical haploid cells

  6. Essential definitions: (sister) chromatids • Chromatid: one of two identical halves (sister chromatids) of a replicated chromosome • NB: following crossing over, sister chromatids are no longer identical!

  7. The process of pairing is called synapsis

  8. Getting to grips with meiosis • Meiosis – the movie • Short summary • Fabulous website based tutorial • Step through from Sumanas

  9. Diploid germ cell chromosomes duplicate during S phase BEFORE meiosis

  10. Homework for Monday Create a document which outlines the process of meiosis AND explains one disease that is caused by an error during meiosis • Your document must be accurate, must demonstrate knowledge, and must be creative • Label AT LEAST: gene; chromosome; DNA, crossing over and all the steps of meiosis • Provide a summary of ONE disease that results from an error during meiosis (a non-disjunction disorder)

  11. Meiosis is a two step process • Meiosis 1 separates the homologous pairs of chromosomes: this is the reduction division • Meiosis 2 separates the sister chromatids (resembles mitosis) • One single diploid cell produces 4 non-identical haploid cells

  12. Essential definitions: homologous chromosomes • Human somatic cells have 22 homologous chromosome pairs and one non-homologous pair • One maternal/ one paternal • Same size and structure • Same genes at same loci • Alleles may differ

  13. Essential definitions: (sister) chromatids • Chromatid: one of two identical halves (sister chromatids) of a replicated chromosome • NB: following crossing over, sister chromatids are no longer identical!

  14. Crossing over and recombination • homologous (duplicated) chromosomes associate during prophase 1 of meiosis • The process of pairing is called synapsis • Watch in detail here

  15. Meiosis and genetic variation

  16. Problems during meiosis

  17. Non-disjunction Production of gametes with an abnormal chromosome number

  18. Down’s Syndrome (Trisomy 21) Ten things people with Down’s Syndrome would like you to know Most commonly due to non-disjunction in the female gamete during anaphase I/II Characteristic facial features Characteristic beautiful, happy nature Wide range of severity of disability

  19. Identifying chromosomes (karyotyping) Chromosomes are lined up in their homologous pairs according to: • Size (1 largest – 22 smallest) • Shape – position of the centromere • Specific banding (staining) patterns using dyes (Giemsa) More later! • and in more detail here

  20. Genetics and Inheritance • Page 197 – 204

  21. Essential vocabulary of genetics: • Gene: A length of DNA that is the unit of heredity • Genotype: The genetic make-up of an organism, in terms of the alleles present • Allele: Any of two or more alternative forms of a gene • Phenotype (trait): Physical or other features of an organism. Caused by combination of genotype AND environment • Autosome: Any chromosome which is not a sex chromosome

  22. Essential definitions: homologous chromosomes • Human somatic cells have 22 homologous chromosome pairs and one non-homologous pair • Each chromosome in a homologous pair contains genes for the same characteristic in the same position • One maternal/ one paternal • Same size and structure • Same genes at same loci • Alleles may differ

  23. Each cell has (at least) 2 genes for any characteristic Homozygous Homologous chromosomes have identical alleles of a particular gene. Two identical homozygous individuals that breed together will always have the same characteristics ‘Pure breeding’/’wild type’ Heterozygous: Chromosomes have two different alleles of a particular gene (Ff). • ‘not ‘’pure breeding’…

  24. Alleles

  25. Dominant and recessive alleles • A dominant allele (e.g. F) will be expressed if it is present • A recessive allele (e.g. f) will only be expressed when there is no dominant allele of the gene present • Codominant alleles (eg IA and IB) are both equally expressed

  26. Some ‘celebrity genes’ • BRAC1 and 2

  27. Celebrity genes (2) Mutations in the CTFR gene cause cystic fibrosis

  28. Celebrity genes (3) APOE4 increases the risk of Alzheimer’s Disease

  29. Working out genetic crosses • Genetic diagrams (Punnet Squares) • Pedigree Charts

  30. Working out single trait inheritance (monohybrid crosses) Monohybrid cross: a mating between two individuals who have different alleles at one gene locus

  31. Working out single trait inheritance • Is the gene located on an autosome (chromosome 1 – 22 in humans) or on a sex chromosome (X/Y- in which case inheritance is sex-linked) • Does the gene have 2 or more than two alleles? • Is the pattern of gene expression dominant/recessive or co-dominant?

  32. Working out monohybrid crosses Always list: • EACH parent’s phenotype (e.g. green pea/ cystic fibrosis free) • EACH parent’s genotype (2 alleles for each parent) • 2 gametes for each parent • F1 generation genotypes (and proportions) • F1 generation phenotypes (and proportions)

  33. An example: cystic fibrosis • An explanation of the disease • Life with cystic fibrosis

  34. Cystic fibrosis is disease associated with expression of a recessive gene

  35. Convention for working out monohybrid crosses

  36. Working out inheritance: Punnet Squares A chart that shows all the possible combinations of alleles that can result from a genetic cross Introduction to Punnett Squares

  37. Steps in Making a PunnettSquare 1. Draw a square and divide it into four. 2. The alleles for one parent go on the top. The alleles for the other parent go down the side. 3. The boxes are like a multiplication problem, with one allele contributed by each parent. I can only give 1/2 of my DNA to my offspring, so I will either give my baby plant a T OR a t. Tt

  38. One Trait Inheritance • T = tall, t = short • Complete the punnet square in your notes. • Label the P gametes • Label the F1 generation • What is the phenotypic ratio? • What is the geneotypic ratio?

  39. One Trait Inheritance P gametes F1 generation Phenotypic Ratio = 3:1 Genotypic Ratio = 1:2:1 TT Tt Tt tt

  40. Cystic fibrosis is disease associated with expression of a recessive gene

  41. Cystic fibrosis Punnet Squares (1)

  42. Cystic fibrosis Punnet Squares (2)

  43. Working out inheritance: Genetic Diagrams Genetic diagrams

  44. Pedigree Charts • A simple introduction

  45. CODOMINANCE Some genes have alleles that are both expressed in the heterozygote individuals

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