1. Meiosis and Sexual Reproduction Notes
To be used with Meiosis and Sexual Reproduction Guided Notes

2. Before Meiosis lets look back at Mitosis

3. Genes and Heredity Heredity -
the passing of traits from parents to offspring.
Genetics -
the study of heredity (the passing of traits)
Each human cell contains 30 thousand different genes

4. Genes and Heredity Genes:
Factors that control organism traits or characteristics.
Part of a chromosome containing the genetic code
Passed on from parent to offspring.
All of your genes are located
on 23 pairs of chromosomes

5. Alleles T t t T Alleles: part of a gene that is located on a
chromosome.
Example:
Height(gene):
tallness or shortness(alleles)
The alleles determine
how each gene is expressed.
At least two alleles for one gene.
Locus: Location of gene on
a chromosome. T T t t

6. Chromosomes
Sister
Chromatid
Chromosome
Homologous Chromosome

7. Homologous Chromosomes:
-a pair of chromosomes that contain genes for the same traits.
-one chromosome is from mom the other from dad.
-same size & centromeres are in same location.

8. Amniocentesis Amniocentesis:
a medical procedure used in prenatal diagnosis of chromosomal abnormalities.
Chromosomes are taken from the
amniotic fluid.

9. Karyotype The chromosomes from the amniotic fluid are
then placed on a karyotype.
A karyotype is a chart
of an organism’s chromosomes.

10. Karyotype Next, the chromosomes are matched up according to:
1. if they came from mom or dad.
2. how tall they are.
3. centromere location.

11. Karyotype A karyotype can reveal if a person…
1. is, male or female
2. has a normal number of chromosomes
3. has an abnormal number of chromosomes.
Example: Down’s syndrome

12. Meiosis
Meiosis:
A type of cell division where the chromosome number is reduced to half.
The process in which cells undergo two dividing phases to form
gametes.
Meiosis only produces sex cells (gametes).

13. Meiosis Gametes are your sex cells. Your egg and sperm cells.
Sexual reproduction
(sperm + egg)produces a zygote.

14. Meiosis

15. Diploid vs. Haploid
Diploid Number (2n): the number of chromosomes found in all body cells.
Humans 46.
-found in the somatic(body) cells
Haploid Number (n): 1/2 the diploid number of chromosomes. Humans 23.
found in the egg and sperm cells of a species
DIPLOID
HAPLOID

16. Diploid vs. Haploid
Organism Diploid # (body cells) Haploid # (sex cells)
Human 46
Chimpanzee
Dog 78
Fruit fly
Garden pea 14
Adder’s fern 23 48 39 8 7
630

17. Terms Gametes: eggs or sperm Gonads:
specialized organs in higher animals where the gametes are made
Ovaries:
female gonads
Testes:
male gonads

18. Meiosis Meiosis I Meiosis II Has all the phases mitosis has. I P M A T
Has all the phases meiosis I has,
except Interphase P M A T

19. Prophase I of Meiosis During Prophase 1 crossing over takes place.
Crossing over is : the exchange of chromosome pieces.
Crossing over increases the variability of the offspring
This is why the offspring of sexual reproduction show many variations
- Crossing over occurs only during Prophase I

20. Mitosis vs. Meiosis

21. Problems during Meiosis
Normally, homologous chromosomes separate and move toward opposite poles of the cell.
Problems during anaphase: this disorder is called non Disjunction
Nondisjunction: the failure of homologous chromosomes to separate

22. Nondisjunction
Down's syndrome: results from the nondisjunction of chromosome 21
individual has an extra 21st chromosome

23. Down’s Syndrome Rates

24. Mistakes in Mitosis can be Good
polyploidy:
having an entire extra set of chromosomes
Will result in the 3n or 4n number of chromosomes
- Many plants are a result of polyploidy; banana & day lily

25. Summary of Mitosis & Meiosis
1. Meiosis is very similar to two divisions of mitosis.
2. The diploid number (2n) of chromosomes is reduced by half to the haploid number (n)
3. Eggs and sperm are formed
Crossing Over causes lots of variations
Variations rarely occur in MITOSIS
Variations often occur in MEIOSIS

26. Summary Mitosis is associated with asexual reproduction.
Mitosis takes place in somatic (body) cells.
What is produced from mitosis?
Two identical daughter cells How many? 4
10. Meiosis is associated with sexual reproduction.
Meiosis takes place in sex cells.
Meiosis produces gametes and three polar bodies.