1. Genes are on chromosome pairs
Inheritance happens through
Sexual reproduction: a cell containing genetic information from the mother and a cell containing genetic information from the father combine into a completely new cell, which becomes the offspring
Genes are on chromosome pairs
Processes are coded for by genes: a unit of heredity that occupies a specific location on a chromosome and code for a particular product
Heredity is the passing of genes from parents to offspring
Genes code for the expression of traits
Traits are not inherited: the gene code for the trait is.
Many genes can code for one trait

2. Genes are on chromosome pairs
Cells contain pairs of chromosomes
One chromosome of each pair coming from each of two parents
Homolog: chromosomes in a pair
Sites where specific genes are located
Homologous Chromosomes

3. There is a gene code for a trait at a specific site on a chromosome
EX: plant height may be at site A on a pair of homologs
Both homologs have the gene for height at site A, but the genes may be different (tall vs short)
EX: flowers color may be at site B on a pair of homologs
Both homologs have the gene for color at site B, but the genes may be different (purple vs white)

4. Chapter 4: Patterns of Heredity
4.1 Living things inherit traits in patterns
4.2 Patterns of heredity can be predicted
4.3 DNA is divided during meiosis
4.4 Cells use DNA and RNA to make proteins
4.3 Before you learned:
Mitosis produces two genetically identical cells
In sexual reproduction, offspring inherit traits from both parents
Genetic traits are inherited in predictable patterns
4.3 Now, you will learn:
Why meiosis is necessary for sexual reproduction
How cells and chromosomes divide during meiosis
How meiosis differs from mitosis

5. Meiosis is necessary for sexual reproduction body cells vs reproductive cells
Cells containing genetic information from each the mother and father combine to form a completely new cell: becomes the offspring
The offspring has some genetic material from each parent
Body cells (most human cells) contain 46 chromosomes (23 pairs)
this is a 2n cell, or a diploid cell
n tells you the # of chromosomes in one set
Diploid means two sets of chromosomes: 2 x 23
Humans: 23 sets of chromosomes, 2 x 23 = 46 total
Fruit fly: 4 sets of chromosomes, 2 x 4 = 8

6. Meiosis is necessary for sexual reproduction body cells vs reproductive cells
Gamete (reproductive cell): cells that contain half the usual number of chromosomes (46/2 = 23) – one from each pair: this is a 1n cell, or a haploid cell
Only found in the reproductive organs of plants and animals
Just the female gamete: egg cell = 1n
Just the male gamete: sperm cell = 1n
Fertilized egg cell = 2n  develops into an offspring
Ex: gamete of human: n cells, 23 unpaired chromosomes
Ex: gamete of fruit fly: n cells, 4 unpaired chromosomes

7. Fertilization Two gametes combine to become a 2n cell that can grow into a new offspring. humans: egg (23 chromosomes) + sperm (23 chromosomes) = fertilized egg cell (46 chromosomes)
Body cells (most human cells) contain 46 chromosomes: this is a 2n cell, or a diploid cell
Gamete: cells that contain half the usual number of chromosomes: this is a 1n cell, or a haploid cell
Just the female gamete - egg cell = 1n
Just the male gamete – sperm cell = 1n
Fertilized egg cell = 2n  develops into an offspring

8. Meiosis Body cells divide by mitosis
Produces two daughter cells, each containing exact copies of the chromosomes in the parent cell
Each daughter cell is a standard diploid cell: 2n
To produce gametes (haploid), need a different kind of division: Meiosis
Produces haploid, 1n, cells
A single cell goes through two divisions:
Meiosis I
Meiosis II
Only in the reproductive tissues of an organism

9. Meiosis I
BEFORE Meiosis: DNA in each chromosome of the parent cell is copied
a cell ready to divide has twice the usual amount of DNA…therefore, for a cell to have half the amount of DNA, two divisions are necessary
Four steps in Meiosis I:
Prophase I: Chromosomes pair up with their partner
Two sets of each of the chromosome pairs in the parent cell
Each chromosome pair is attached together in sets of doubled homologs
Metaphase I: each set of chromosome pairs lines up along the center of the cell
Anaphase I: The two copies of one homolog are pulled apart from the two copies of the other homolog
Telophase I and Cytokinesis: A new cell membrane forms at the center of the cell; parent cell divides  two daughter cells

10. Meiosis II In Meiosis I, two daughter cells formed
Chromosomes of these two cells are not copied before Meiosis II
Both these cells divide during Meiosis II  4 daughter cells
5. Prophase II: the two copies of each n chromosome are attached together
Metaphase II: The chromosomes line up along each cell’s center
Anaphase II: The two attached copies of each chromosome separate and are pulled to opposite poles in each cell
Telophase II and Cytokinesis: A new cell membrane forms in the center of each cell, as each cell divides into two 1n daughter cells  4: 1n cells

11. http://highered. mcgraw-hill

12. Meiosis
One cell in an organism’s reproductive system divides twice to form four 1n cells
In males, these gametes become sperm
In females, at least one of these cells becomes an egg
In some species (humans) only one of four daughter cells becomes and egg
The rest dissolve back into the organism or are never produced

13. Meiosis vs Mitosis
Only cells that are to become gametes go through meiosis
A cell that divides by meiosis undergoes two divisions, but the chromosomes are not copied before the 2nd division…in mitosis, chromosomes are always copied before dividing
Daughter cells produced by meiosis (haploid/1n) contain only ½ the genetic material of the parent cell (one of each chromosome)
Daughter cells produced by mitosis (diploid/2n) contain exactly the same genetic material as the parent (pairs of chromosomes)

14. http://highered. mcgraw-hill

16. try it
Meiosis

17. How Cells Divide

19. A meiosis I, B meiosis II, C interphase, D prophase I, E metaphase I, F anaphase I, G telophase I, H prophase II, I metaphase II, J anaphase II, K telophase II, L four haploid cells