Sexual reproduction and the diversity of life
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Sexual Reproduction and the Diversity of Life. BC Science Probe 9 Section 3.2 Pages 79-82. Fertilization Produces Diploid Cells. Fertilization: The joining or fusing of two gametes. Gametes are produced by meiosis

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Sexual Reproduction and the Diversity of Life

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Sexual reproduction and the diversity of life

Sexual Reproduction and the Diversity of Life

BC Science Probe 9

Section 3.2

Pages 79-82


Fertilization produces diploid cells

Fertilization Produces Diploid Cells

  • Fertilization: The joining or fusing of two gametes.

    • Gametes are produced by meiosis

    • They are haploid (only have ½ the regular number of chromosomes of the parent cell)

    • When two gametes fuse during fertilization, they make a diploid cell (a cell with a full set of chromosomes)


Fertilization produces diploid cells1

Fertilization Produces Diploid Cells

  • The first diploid (2n) cell of the offspring is called the zygote.

    sperm(n) + egg (n) = zygote (2n)


Fertilization produces diploid cells2

Fertilization Produces Diploid Cells

  • Zygote:

    • Gets half of its chromosomes from each parent.

    • Human gametes each have 23 chromosomes, so a human zygote will have 46, then divide by mitosis to produce more genetically identical cells with 46 chromosomes


Diversity among offspring

Diversity Among Offspring

  • Diversity = variation or differences

  • There is diversity among different species and also within a species.

  • Sexual reproduction creates diversity


Diversity among offspring1

Diversity Among Offspring

  • It’s the homologous pairs of chromosomes that produce the variations among members of a species.

    • Each of the chromosomes in the homologous pair have corresponding genes (genes that code for the same trait ex. hairline)

    • But… these genes can be slightly different from one another!


Diversity among offspring2

Diversity Among Offspring

  • The different forms of the same gene are called alleles.

    • Back to the hairline example: there are two different alleles.

      • One is for a straight hairline

      • One is for a widow’s peak


Diversity among offspring3

Diversity Among Offspring

  • The allele for a widow’s peak is dominant.

    • This means that it will express its trait (show up) if it is present


Diversity among offspring4

Diversity Among Offspring

  • The allele for a straight hairline is recessive.

    • This means that it will only show up if both chromosomes in the homologous pair have the recessive allele.


Diversity among offspring5

Diversity Among Offspring

  • If an individual has one of each allele, the dominant one gets expressed.


Diversity among offspring6

Diversity Among Offspring

  • Some alleles are not dominant or recessive.

  • There are such things as incomplete dominance and codominance.


Diversity among offspring7

Diversity Among Offspring

  • Incomplete dominance:

    • Two different alleles produce a mixture of the traits.

    • Red carnation + white carnation = pink carnation


Diversity among offspring8

Diversity Among Offspring

  • Codominance is when both traits get expressed.

    • This horse has one allele for white hair and one for red. Both get expressed.


Diversity among offspring9

Diversity Among Offspring

  • There are even some traits that are controlled by more than one gene!

  • Human eye colour is one of these traits. That’s why there are so many variations!


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