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Heredity (part 2): Present Day Understanding on Heredity based on Mendel findings

Students will be able to: <br>- define a gene as a unit of inheritance and distinguish clearly between the terms gene and allele <br>- explain the terms dominant, recessive, codominant, homozygous, heterozygous, phenotype and <br>genotype

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Heredity (part 2): Present Day Understanding on Heredity based on Mendel findings

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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. 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

  5. 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

  6. 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.

  7. 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

  8. Genotype = the specific combination of alleles; represented by letters Phenotype = what trait looks (acts) like

  9. Test yourself Pair of homologous chromosomes A gene locus A pair of alleles 3 pairs of alleles

  10. Relationship between DNA, Chromosomes and Genes

  11. Homozygous dominant parent Homozygous recessive parent Mendel’s Theory of Segregation C c C c (chromosomes duplicated before meiosis) C c C c C c C c meiosis I C C c c C C c c meiosis II C C C C c c c c gametes gametes C Fertilization produces heterozygous offspring c

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