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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: 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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  1. Sexual Reproduction and the Diversity of Life BC Science Probe 9 Section 3.2 Pages 79-82

  2. 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)

  3. Fertilization Produces Diploid Cells • The first diploid (2n) cell of the offspring is called the zygote. sperm(n) + egg (n) = zygote (2n)

  4. 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

  5. Diversity Among Offspring • Diversity = variation or differences • There is diversity among different species and also within a species. • Sexual reproduction creates diversity

  6. 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!

  7. 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

  8. 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

  9. 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.

  10. Diversity Among Offspring • If an individual has one of each allele, the dominant one gets expressed.

  11. Diversity Among Offspring • Some alleles are not dominant or recessive. • There are such things as incomplete dominance and codominance.

  12. Diversity Among Offspring • Incomplete dominance: • Two different alleles produce a mixture of the traits. • Red carnation + white carnation = pink carnation

  13. 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.

  14. 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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