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Inheritance Genes And Cell Division

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Notes de leçon

Chromosomes, Genes & Proteins

  • Chromosomes are thread-like structures in the nucleus made of DNA.
  • A gene is a short length of DNA on a chromosome that codes for a specific protein (e.g., collagen, enzyme, hormone).
  • Alleles are alternative forms of a gene (e.g., blue, green, brown alleles for eye colour).
  • Genes determine characteristics by coding for proteins.

The Inheritance of Sex

  • Sex is determined by sex chromosomes: females are XX, males are XY.
  • Only males can pass on a Y chromosome, determining the child's sex.
  • Half of sperm carry X, half carry Y; if X fertilises egg (X), offspring is female (XX); if Y fertilises egg, offspring is male (XY).
  • Punnett square for sex inheritance shows 50% probability of each sex.

Control of Gene Expression (Extended)

  • Diploid cells have two sets of chromosomes (e.g., human body cells: 46 chromosomes).
  • Haploid cells have one set of chromosomes (e.g., human gametes: 23 chromosomes).
  • Gametes (sperm and egg) are haploid; fertilisation restores diploid number.

Mitosis (Extended)

  • Mitosis is nuclear division producing genetically identical diploid cells.
  • Chromosomes replicate before division, ensuring each daughter cell has the same number of chromosomes.
  • Mitosis is used for growth, repair of damaged tissues, replacement of cells, and asexual reproduction.

Meiosis (Extended)

  • Meiosis is a reduction division that halves chromosome number from diploid to haploid.
  • It produces four genetically different haploid cells (gametes).
  • Meiosis ensures genetic variation and maintains constant chromosome number after fertilisation.

Monohybrid Inheritance

  • Inheritance is the transmission of genetic information from parents to offspring.
  • Genotype is the combination of alleles; phenotype is the observable characteristic.
  • Dominant allele masks a recessive allele; recessive only shows when homozygous.
  • Homozygous = two identical alleles; heterozygous = two different alleles.
  • Monohybrid inheritance involves a single gene; Punnett squares predict offspring ratios.
  • Example: tall (T) dominant over short (t); cross TT × tt gives all Tt (tall); Tt × Tt gives 3:1 ratio tall:short.
  • Pedigree charts trace inheritance patterns through families, using squares (males) and circles (females).

Diapos

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Questions d'entraînement

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  1. 1.Where are chromosomes located in a cell?

    Easy
    • AIn the cytoplasm
    • BIn the nucleus
    • COn the cell membrane
    • DIn the mitochondria
  2. 2.What is a short length of DNA that codes for a specific protein called?

    Easy
  3. 3.Biological females have the sex chromosomes XY.

    Easy

    True or false?

  4. 4.Complete the sentence about cell division.

    Easy

    Mitosis produces genetically ____ cells.

  5. 5.How many chromosomes are in a human diploid cell?

    Easy
    • A46
    • B41
    • C51
    • D56
  6. 6.Match each cell division type to its description.

    Medium
    • Mitosis
    • Meiosis
    • Produces genetically identical cells
    • Produces genetically different cells
    • Reduces chromosome number by half
  7. 7.Arrange the following events in the correct order for meiosis:

    Medium
    • Chromosomes replicate
    • Homologous chromosomes separate
    • Cell divides twice
    • Four haploid cells are formed
  8. 8.In a monohybrid cross between two heterozygous tall plants (Tt x Tt), what is the expected phenotypic ratio?

    Medium
    • A1:2:1
    • B3:1
    • C1:1
    • D9:3:3:1

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