1. Living organisms are distinguished by their ability to reproduce their own kind
Offspring resemble their parents
They have similar characteristics

2. (Do you look exactly like your brother or sister?)
Heredity – the transmission of traits from one generation to the next.
(Do you look exactly like your brother or sister?)
Even though there is similarity between offspring and parents, there is also variation
Variation helps to make each species unique.

3. Inheritance of Genes
Genes – the chemical factors that determine traits.
Genes are segments of DNA
They are located on chromosomes in the cells nucleus
Humans inherit tens of thousands of genes from their parents.
This accounts for family resemblances

4. Genetics is the scientific study of heredity.

5. Gregor Mendel
Is known as the father of Genetics because he studied the transmission of traits from one generation to the next.
He came up with several principles

6. Principles of Genetics
A. Each organism must inherit a single copy of every gene from each of its “parents”
B. When an organism produces is own gametes (sex cells), those two sets of genes must be separated from each other so that each cell contains just one set of genes.
(we get only half of our chromosomes from each parent)

7. In animals and plants reproductive cells transmit the genes.
Gametes (sex cells) – are the vehicles that transmit the genes.
Females = egg cells
Males = sperm cells

8. Chromosome Number
In humans, each somatic cell (body cell)-any cell other than a sex cell, has 46 chromosomes.

9. Check for Understanding
How is a gamete different from a somatic cell?

10. Any cell with two chromosome sets is called a diploid cell.
2 chromosomes after replication

11. These two sets of chromosomes are arranged in homologous pairs, meaning…
One set is inherited
from the mother, the
other from the father.
Homo- same
Pairs have similar genetic information on them. Note, same size

12. Diploid is abbreviated 2N
So human body cells (somatic cells) are diploid and (2N = 46)
Skin cells
Nerve cells

13. Gametes (sex cells), contain only a single set of chromosomes.
These cells are haploid, which means “one-set”.
Haploid is abbreviated (N)
So human gametes are haploid and (N = 23)

14. Check for understanding
If a cell is N=4
How many chromosomes would be in a body cell that is 2N?
If a sex cell has 12 chromosomes, how many chromosomes would be in a somatic cell?
If a body cell is 2N = 8
How many chromosomes would be in the animals sex cells? N=

15. How are haploid gametes produced from diploid cells?

16. Meiosis… an overview A reduction in the number of chromosomes.
Diploid cells produce haploid gametes.
Takes place where gametes are formed (in humans, in the ovaries and testes).
Homologous chromosomes are separated.
Each new cell produced has only one set of chromosomes.
Involves two distinct divisions, called meiosis I and meiosis II.
Allows for genetic variations.

17. Meiosis
Meiosis
Takes place in two sets of divisions, meiosis I and meiosis II
Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half.

18. Meiosis I - Reduction Meiosis II-Division
Reduces the number of chromosomes from diploid to haploid
Meiosis II-Division
Produces four haploid daughter cells

19. Division I – Meiosis I 6 chromosomes. 2 sets = diploid
Homologous pairs line up across the center of the cell. Or pairs line up across the center
Homologous chromosomes separate. Or chromosome pairs
Sister chromatids remain attached
Homologous chrom. Pair. Or chromosomes form pairs
Cell prepares for division
Specific type of body cell called a germ cell
Form a structure called a tetrad. Which is 4 chromatids of a homologous pair
Crossing over occurs.
Which is the exchange of genetic information

20. Division II - Meiosis II
Meiosis I – Con’t
Division II - Meiosis II
2 cells are produced
Similar to mitosis
Chromosomes line up across the center of the cell
Sister Chromatids separate and move to opposite sides
4 cells are produced
Haploid or Diploid?
Still Haploid cells

21. Sex Cell Formation Spermatogenesis- production of sperm
Process takes about hours.
Males produce sperm.
From one germ cell, 4 cells will be produced that will become sperm.

22. Sperm Development
Males contain germ cells called spermatogonium within their testes.
These cells will undergo both divisions of meiosis to produce sperm cells with half the number of chromosomes.
This division begins when signaled by hormones.
Men produce sperm throughout their life time.

23. Sex Cell Formation Oogenesis- egg cell production Takes 15-30 yrs.
In females, the cell divisions at the end of meiosis I and meiosis II are uneven, so that a single cell, which becomes an egg, receives most of the cytoplasm. Cytoplasm contains nutrients and we want that egg to have lots of nutrients.
The three other cells do not form eggs and are called polar bodies
Oogenesis- egg cell production
You tube : nursereview.org animation on oogenesis Miracle of Human Life 14min

24. Division I – Meiosis I
You must also know all the other happenings in the cell that were similar to mitosis
Interphase Prophase I metaphase I anaphase I
Cell prepares for division
(homologous chromosomes) pair
Form a structure called a (tetrad)
-which is (4) chromatids
(crossing over) occurs
- which is the (exchange) of
genetic information
(homologous pairs) line up across the center of the cell
(homologous pairs) separate
(sister chromatids) remain attached
Meiosis I is the reduction phase because the chromosome number is reduced by half

25. Division II - Meiosis II
Meiosis I – Con’t
Division II - Meiosis II
(2) Cells are produced
Cells are Haploid
Nuclear envelope breaks down
Spindle fibers form
Centrosomes move
(chromosomes) line up across the center of the cell
(sister chromatids) separate and move to opposite sides
(4) Cells are produced
Cells are Hapolid
Meiosis II is the division phase because we end up with a total of four cells