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DNA and inheritance

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Apuntes de la lección

Inheritance

  • Inheritance is the passing on of traits from one generation to the next.
  • Characteristics like eye colour and height are inherited from parents.
  • You inherit one chromosome of each pair from your mother and the other from your father.

Chromosomes

  • Chromosomes are thread-like structures found in the nucleus of every cell.
  • Humans have 46 chromosomes arranged in 23 pairs.
  • Each parent contributes one chromosome to each pair.

DNA

  • DNA (deoxyribonucleic acid) is the molecule that makes up chromosomes.
  • DNA carries genetic instructions that tell cells how to function and determine traits.
  • DNA has a double-helix structure, like a twisted ladder.

Genes

  • Genes are specific segments of DNA that carry instructions for a specific characteristic.
  • For example, one gene determines eye colour, another determines blood type.
  • Humans have thousands of genes that work together to determine physical traits and some aspects of personality.

Dominant and Recessive Genes

  • Dominant genes: if you inherit the dominant version from one parent, that trait is more likely to show.
  • Recessive genes: the trait only appears if you inherit the recessive version from both parents.

Discovery of DNA Structure

  • In the 1950s, James Watson and Francis Crick determined the structure of DNA.
  • They built on the work of Rosalind Franklin and Maurice Wilkins using X-ray crystallography.
  • Raymond Gosling produced Photo 51, which provided crucial clues for the double-helix model.

DNA double helix structure with sugar–phosphate backbones and complementary base pairs (A–T, C–G).

DNA — double helixSugar–phosphate backboneBase pairHydrogen bondsA – TC – G

Monohybrid cross showing dominant and recessive inheritance with 3:1 phenotype ratio.

Genetic cross: Bb × Bbseed shape (B=round dominant, b=wrinkled)Parent 1 gametesParent 2 gametesBbBbBBBbBbbbGenotype ratio 1 BB : 2 Bb : 1 bbPhenotype ratio 3 dominant : 1 recessive

Diapositivas

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Preguntas de práctica

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  1. 1.What does DNA stand for?

    Easy
    • ADeoxyribonucleic acid
    • BDeoxyribose nucleic acid
    • CRibonucleic acid
    • DDeoxyribonucleotide acid
  2. 2.How many chromosomes do humans have in each cell?

    Easy
    • A46
    • B23
    • C92
    • D48
  3. 3.What is the shape of the DNA molecule?

    Easy
    DNA — double helixSugar–phosphate backboneBase pairHydrogen bondsA – TC – G
    • ADouble helix
    • BSingle helix
    • CTriple helix
    • DStraight ladder
  4. 4.Which of the following correctly describes the relationship between chromosomes, DNA, and genes?

    Easy
    • AChromosomes are made of DNA, and genes are segments of DNA.
    • BDNA is made of chromosomes, and genes are segments of chromosomes.
    • CGenes are made of chromosomes, and DNA is a type of gene.
    • DChromosomes are made of genes, and DNA is a type of chromosome.
  5. 5.If a trait is recessive, when will it appear in an individual?

    Easy
    • AOnly if the individual inherits the recessive version from both parents
    • BIf the individual inherits the recessive version from at least one parent
    • COnly if the individual inherits the dominant version from both parents
    • DIt always appears regardless of inheritance
  6. 6.Who produced 'Photo 51', which was crucial in determining the structure of DNA?

    Easy
    • ARaymond Gosling
    • BRosalind Franklin
    • CMaurice Wilkins
    • DJames Watson
  7. 7.Where are chromosomes found in a cell?

    Easy
    • ANucleus
    • BCytoplasm
    • CCell membrane
    • DMitochondria
  8. 8.What is a gene?

    Easy
    • AA segment of DNA that carries instructions for a specific characteristic
    • BA type of chromosome
    • CThe entire DNA molecule
    • DA protein that determines traits

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