The Process of Sexual Reproduction
Sexual reproduction is the process by which offspring are produced through the combination of genetic material from two different parents. This process involves the formation of sex cells, or gametes, through a specialized type of
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About The Process of Sexual Reproduction
PowerPoint presentation about 'The Process of Sexual Reproduction'. This presentation describes the topic on Sexual reproduction is the process by which offspring are produced through the combination of genetic material from two different parents. This process involves the formation of sex cells, or gametes, through a specialized type of. The key topics included in this slideshow are . Download this presentation absolutely free.
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Slide2SEXUAL REPRODUCTIONSex cells formed by meiosis Requires 2 parents Offspring not identical The process that results in the formation of gametes Sex cells, egg or sperm, which have haploid chromosomes Haploid means HALF, as in the number of chromosomes, written as n Meiosis Gametes Haploid
Slide3FertilizationThe union of an egg and a sperm The cell that is formed when the egg becomes fertilized by the sperm. This results in a full set of chromosomes. All body cells except for sex cells that have diploid chromosomes Diploid means they have chromosome found in pairs, written as 2n n n 2n Zygote Somatic Cells Diploid
Slide4Homologous ChromosomesSimilar chromosomes that are found in pairs. The paired chromosomes come from the mother and father. * Human body cells have 46 chromosomes each * Human body cells have 23 homologous pairs Meiosis and Fertilization Important for survival of many species, because these processes result in genetic variation of offspring. Meiosis A kind of cell division that results in gametes (sex cells) with half the number of chromosomes.
Slide5A. Gametes do not have homologous pairs, but instead they have only half the chromosomes from each pair. Gametes are referred to as haploid (n). B. When fertilization occurs, the zygote will have a normal number of chromosomes (2n). C. In meiosis, specialized cells divide 2 times producing 4 daughter cells.
Slide6Phases of Meiosis(2 Cell divisions – Meiosis I & Meiosis II) MEIOSIS I Prophase I Homologous chromosomes pair together to form tetrads During Prophase I, crossing over occurs between homologous chromosomes and genes are exchanged causing genetic variation
Slide7Metaphase ISpindle fibers attach to chromosomes and line them up in the middle of the cell. Anaphase I The fibers pull the homologous chromosomes apart. This is called disjunction . Chromosomes move toward opposite sides of the cell.
Slide8Telophase IDuring Telophase I and cytokinesis, the nuclear membrane forms and the cell splits into two new cells. **** The Chromosome number is reduced to half during Meiosis I forming haploid (n) daughter cells
Slide9MEIOSIS IIProphase II Spindle fibers form and attach to double stranded chromosomes Metaphase II Chromosomes line up in the middle of the cell
Slide10Anaphase IISister chromatids separate and move towards opposite sides of the cell Telophase II Cells divide, resulting in 4 haploid cells – gametes (sex cells)
Slide11males form 4 haploid cells which develop into 4 spermK K K K K K K K Females form 4 haploid cells which develop into 1 egg and 3 small polar bodies Egg Polar Bodies Small polar bodies are not used and break down.
Slide12MeiosisMeiosis Parent cell – chromosome pair Chromosomes copied 1 st division - pairs split 2 nd division – produces 4 gamete cells with ½ the original no. of chromosomes
Slide13Meiosis – mouse testes Meiosis – mouse testes Parent cell 4 gametes 1 st division 2 nd division
Slide14figure 13.7 the stages of meiotic cell division: Meiosis I
Slide15figure 13.7 the stages of meiotic cell division: Meiosis II
Slide16One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent assortment produces 2 n distinct gametes, where n = the number of unique chromosomes. Independent assortment produces 2 n distinct gametes, where n = the number of unique chromosomes. That’s a lot of diversity by this mechanism alone. That’s a lot of diversity by this mechanism alone. In humans, n = 23 and 2 23 = 6,000,0000 . In humans, n = 23 and 2 23 = 6,000,0000 .
Slide18Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment. Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.
Slide20The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis Mitosis Mitosis The first (and distinguishing) division of meiosis The first (and distinguishing) division of meiosis
Slide22Boy or Girl? The Y Chromosome “Decides” Boy or Girl? The Y Chromosome “Decides” X chromosome X chromosome Y chromosome Y chromosome
Slide23Boy or Girl? The Y Chromosome “Decides” Boy or Girl? The Y Chromosome “Decides”
Slide24Meiosis – division error Meiosis – division error Chromosome pair
Slide25Meiosis error - fertilization Meiosis error - fertilization Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’. Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’. In humans this often occurs with the 21 st pair – producing a child with Downs Syndrome In humans this often occurs with the 21 st pair – producing a child with Downs Syndrome
Slide2621 trisomy – Downs Syndrome 21 trisomy – Downs Syndrome Can you see the extra 21 st chromosome? Is this person male or female?