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Meiotic Cell D ivision and Sexual Reproduction

Meiotic Cell D ivision and Sexual Reproduction. General Biology Name_____________________. What is Meiosis?. ___________is a type of cell division in which sexually reproducing organisms produce sex cells that contain _______of the normal number of chromosomes for that organism.

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Meiotic Cell D ivision and Sexual Reproduction

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  1. Meiotic Cell Division and Sexual Reproduction General Biology Name_____________________

  2. What is Meiosis? • ___________is a type of cell division in which sexually reproducing organisms produce sex cells that contain _______of the normal number of chromosomes for that organism. • At the time of _______________, each genetically unique egg and sperm will provide half of the genetic instructions to form a unique offspring. • Meiosis guarantees genetic ____________in offspring created by sexual reproduction.

  3. Asexual vs. Sexual Reproduction

  4. Where does meiosis take place? • Start with a cell that has the full number of chromosomes typical for this species – this is known as a ____________cell. • A diploid cell is one that contains one or more _______of chromosomes, carrying paired genes that determine the traits o the organism. • Meiosis occurs only in certain cells of the organism, such as the _______ or _______ in a human.

  5. Paired chromosomes • DNA replication occurs in preparation for meiosis, so the chromosomes are double armed, each DAC consisting of two identical sister ____________. • A matching pair of chromosomes is called a ______________PAIR. The pair has a maternal homolog and a paternal homolog that were inherited from that organism’s mother and father. • Cells with paired chromosomes are _______(2n). • Cells without paired chromosomes are ______(n).

  6. Homologous Pairs Genetic instructions for Blood type A from mother Genetic instructions for Blood type B from father • Same ______ • Same _______ • Same _______of bands when stained • Have matching ______ in the same locations • BUT the specific form of each gene (called an ________) may differ

  7. Karyotyping Scientists can prepare a __________from a body cell of an adult or baby to look for chromosomal abnormalities (damaged, missing or extra chromosomes).

  8. Meiosis Involves Two Cell Divisions _____________ ____________ During the second cell division (IPMATC-2) we start with a haploid cell that contains double armed chromosomes. The DAC line up single file along the equator, then the sister chromatids are pulled apart. Each cell divides into two haploid cells containing single armed chromosomes. • During he first cell division (IPMATC-1) we start with a diploid cell that contains double armed chromosomes. • The double armed chromosomes line up in pairs along the equator and they may some genes. Then the pairs are pulled apart. • The cell divides into two haploid cells containing DAC.

  9. Meiosis

  10. Meiosis in Males (Spermatogenesis) • One full cycle of meiosis produces ______ haploid cells of ______ size. • In humans these cells will develop into functional _______ cells as they mature in the testes.

  11. Meiosis in Females • One full cycle of meiosis produces FOUR haploid cells but they are ___________ in size. • Since the cytoplasm divides unequally, the result is _____ large ______ cell and ______small nonfunctioning cells called _____bodies. In humans the egg will mature in the ovary.

  12. Meiosis as a Source of Variation • SORTING OF GENES (“Independent Assortment”) • The two members of each homologous pair may carry different alleles, so the way the different pairs randomly line up in relation to other pairs leads to many possible __________________in the sex cells that result.

  13. Meiosis as a Source of Variation • __________________ • As homologous chromosomes pair up during Meiosis 1, they can “swap” or exchange genes. • After separation each set is unique so there are no two sperm or egg cells, even from the same parent, that are alike

  14. Meiosis as a Source of Variation • RECOMBINATION - Each sperm and egg contain a ______________ combination of genetic instructions due to meiosis • At fertilization the full species number of chromosomes is restored. • This unique combination of thousands of genes at fertilization produces an offspring that is genetically ____________ (but not identical) to the parents.

  15. When Meiosis Goes Wrong • _____________ is the failure of chromosomes to separate properly during Meiosis 1 or 2. • The resulting sex cells may have an extra or missing chromosome. • Most of the time, the consequences are so severe that a resulting zygote cannot survive. • _________= having three copies (instead of two) of a chromosome • Ex. Down Syndrome (Trisomy 21) • _________= having one copy (instead of two) of a chromosome • Ex. Turners Syndrome (Females inherit only one sex chromosome) • _________= when part of a chromosome is missing • Ex. Cri-du-Chat (deletion of part of Chromosome #5)

  16. At _______, two haploid _______join to form a diploid __________

  17. In Humans…

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