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Meiosis Biology 2009-2010.

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Presentation on theme: "Meiosis Biology 2009-2010."— Presentation transcript:

1 Meiosis Biology

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

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

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

5 Male Karyotype

6 Female Karyotype

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

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

9 Steps of 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 Homologenous chromosomes- DNA does not have to be the same

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

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

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




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 Biology

18 Numbers 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

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

20 Detection Blood Test 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
Trisomy- gain an extra chromosome Sex Chromosomes- X and Y

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


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

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

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

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


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