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Chapter 19 Heredity Lesson 2 - Present day understanding on heredity based on Mendel’s Experiments
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Chapter 19 Heredity Lesson 2 - Present day understanding on heredity based on Mendel’s Experiments

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  • 1. Present Day Understanding on Heredity based on Mendel’s Findings
  • 2. Key Concepts:
    • In cells, DNA molecules are packaged into chromosomes
    • An unduplicated chromosome consists of one DNA molecule and many associated proteins ( histones )
    • The total number of chromosomes in a body cell ( somatic cell ) is the diploid number (2n)
    • The human diploid number is 46 and consists of a pair of sex chromosomes and 22 pairs of autosomes (non-sex chromosomes)
    • The diploid number consists of one set of chromosomes from each parent
    • The same two chromosomes from different parents = a homologous pair
  • 3. DNA DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone. http:// ghr.nlm.nih.gov/handbook/illustrations/dnastructure
  • 4.  
  • 5. Chromosomes
    • Thread-like structure found in the nucleus on which genetic material is organized
    • Carry the information for making new animal or plant bodies
    • This information is carried in DNA
    Karyotype: A photomicrograph of an individual's chromosomes arranged in a standard format showing the number, size, and shape of each chromosome type
  • 6. Homologous chromosomes
    • Homologous chromosomes mean that diploid cells have two copies of each gene, with one copy coming from mom and one copy coming from dad!
    • - However, the sequences of the two genes do not have to be identical
  • 7. Genes - small fragment of DNA in a chromosome where a piece of genetic (hereditary) info is stored - gene locus = place on the chromosome where the gene resides; controls a particular trait e.g. colour, height, etc.
  • 8. Allele
    • the sequences of the two genes do not have to be identical
    • alternative forms of the same gene
    • - e.g. gene for height may have 2 alleles: short and tall
    Skin Color Height
  • 9. Genotype = the specific combination of alleles; represented by letters Phenotype = what trait looks (acts) like
  • 10. Pair of homologous chromosomes A gene locus A pair of alleles 3 pairs of alleles Test yourself
  • 11. Relationship between DNA, Chromosomes and Genes
  • 12.  
  • 13.  
  • 14. C c Fertilization produces heterozygous offspring meiosis II meiosis I (chromosomes duplicated before meiosis) Homozygous dominant parent Homozygous recessive parent gametes gametes Mendel’s Theory of Segregation C C C C C C C C C C C C C C c c c c c c c c c c c c c c
  • 15. Lesson Objectives
    • (f) explain co-dominance and multiple alleles with reference to the inheritance of the ABO blood group phenotypes - A, B, AB, O, gene alleles I A , I B and I O
    • (g) describe the determination of sex in humans - XX and XY chromosomes
    • (h) describe mutation as a change in the structure of a gene such as in sickle cell anaemia, or in the chromosome number, such as the 47 chromosomes in a condition known as Down Syndrome
    • (i) name radiation and chemicals as factors which may increase the rate of mutation