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Meiosis Biology2009-2010. Meiosis Def: type of cell division that produces 4 cells with half the number of chromosomes as a parent cell Def: type of cell.

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Presentation on theme: "Meiosis Biology2009-2010. Meiosis Def: type of cell division that produces 4 cells with half the number of chromosomes as a parent cell Def: type of cell."— Presentation transcript:

1 Meiosis Biology2009-2010

2 Meiosis Def: type of cell division that produces 4 cells with half the number of chromosomes as a parent cell Def: type of cell division that produces 4 cells with half the number of chromosomes as a parent cell Occurs in the sex organs Occurs in the sex organs Number of chromosomes= 46 or 23 pairs Number of chromosomes= 46 or 23 pairs

3 Homologenous Chromosomes Def: chromosomes that match in shape and size but not necessarily same DNA patterns Def: chromosomes that match in shape and size but not necessarily same DNA patterns Homologous Chromosomes

4 Karyotyping Karyotyping –Def: arrangement of all 46 chromosomes Sex chromosomes Sex chromosomes –The 23 rd pair –Determines the organisms sex –XX= girl –XY=boy

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7 Diploid vs. Haploid Diploid Diploid –2 homologenous sets of chromosomes –Forms the zygote –2n Haploid Haploid –1 set of chromosomes- one from each pair –Occurs in fertilization –n–n–n–n

8 Number of Chromosomes Sex Cells each have half the number of chromosomes (23) Sex Cells each have half the number of chromosomes (23) Zygote (fertilized egg) have 46 chromosomes Zygote (fertilized egg) have 46 chromosomes

9 Steps of meiosis Steps of meiosis Differences between mitosis and meiosis: Differences between mitosis and meiosis: –Meiosis produces 4 offspring cells –Meiosis involves exchanging of genetic material between the Homologous Chromosomes. Sister chromosomes- exact copies of DNA Sister chromosomes- exact copies of DNA Homologenous chromosomes- DNA does not have to be the same Homologenous chromosomes- DNA does not have to be the same

10 Meiosis 1 Prophase 1 Prophase 1 –Homologenous chromosomes stick together forming a tetrad –Crossing over begins Metaphase 1 Metaphase 1 –Crossing over is complete –Chromosomes line up in the center Anaphase 1 Anaphase 1 –Chromosomes migrate towards the opposite poles Telophase 1 Telophase 1 –Each pole has a haploid

11 Crossing Over DEF: DEF: Genetic materials is transferred from one chromosome to another Cross ed over

12 Meiosis 2 Follows the exact same steps as Mitosis except the end results in 4 cells instead of 2 Follows the exact same steps as Mitosis except the end results in 4 cells instead of 2

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16 Chickens have 78 chromosomes in their body cells how many chromosomes do they have in their sex cells? Cats have 38 chromosomes in their diploid cells. How many do they have in their haploid cells?

17 Birth Defects Biology2009-2010

18 Numbers There are 200,000 people born with birth defects every year There are 200,000 people born with birth defects every year To break it down, there are 25 people born with birth defects per hour To break it down, there are 25 people born with birth defects per hour

19 Causes of Birth Defects Drugs/Alcohol/Smoking Drugs/Alcohol/Smoking Radiation/Pollution Radiation/Pollution STD’s STD’s Inheritance Inheritance Malnutrition Malnutrition

20 Detection Blood Test Blood Test Amniocentesis- Amniocentesis- –A sample of the amniotic fluid is taken and then the DNA is checked for Chromosomal defects

21 Chromosomes Monosomy- loss of one chromosome Monosomy- loss of one chromosome Trisomy- gain an extra chromosome Trisomy- gain an extra chromosome Sex Chromosomes- X and Y Sex Chromosomes- X and Y

22 Down Syndrome Occurrence-1/600 births Occurrence-1/600 births Causes- trisomy 21 Causes- trisomy 21 Chance with increased age Chance with increased age –20’s- 1/1500 –40’s-1/44

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24 Homozygous Recessive Traits Found on the X chromosome Found on the X chromosome Passed on from mother’s to their children Passed on from mother’s to their children Examples: Muscular Dystrophy and color blindness Examples: Muscular Dystrophy and color blindness

25 Mutations Definition- change in the DNA by changing one or more genes Definition- change in the DNA by changing one or more genes

26 Mutagens Definition- Agents that cause mutations Definition- Agents that cause mutations Examples: Chemicals, x-rays, radiation, genetic Examples: Chemicals, x-rays, radiation, genetic

27 Twins Fraternal- Two fertilized eggs are implanted in the uterus at one time Fraternal- Two fertilized eggs are implanted in the uterus at one time Identical- one fertilized egg that splits Identical- one fertilized egg that splits

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