1. Most humans have 46 chromosomes (23 pairs) in their body cells.
They have only 23 chromsomes in their gametes.
Why do you think gametes only have half the number of chromsomes?

2. Talk to the people around you about what a Punnett square is used for.

3. Talk to the people around you about the difference between heterozygous and homozygous.

4. Talk to the people around you about the Law of Segregation.

5. Talk to the people around you about the Law of Independent Assortment.

6. Section 10.2 Summary – pages 263-273
Genes do not exist free in the nucleus of a cell; they are lined up on chromosomes.
Typically, a chromosome can contain a thousand or more genes along its length.
Section 10.2 Summary – pages

7. Section 10.2 Summary – pages 263-273
Diploid Cells
A cell with two of each kind of chromosome is called a diploid cell.
Your body cells are diploid, and contain 46 chromosomes.
Section 10.2 Summary – pages

8. Section 10.2 Summary – pages 263-273
Homologous Chromosomes
The two chromosomes of each pair in a diploid cell are called homologous chromosomes.
Each pair of homologous chromosomes has genes for the same traits.
Section 10.2 Summary – pages

9. Section 10.2 Summary – pages 263-273
Haploid Cells
A cell containing one of each kind of chromosome is called a haploid cell.
Organisms produce gametes (sex cells) that contain one of each kind of chromosome.
Section 10.2 Summary – pages

10. Section 10.2 Summary – pages 263-273
Diploid and Haploid Cells
Chromosome Numbers of Common Organisms
Organism
Body Cell (2n)
Gamete (n)
Fruit fly 8 4
Garden pea 14 7
Corn 20 10
Tomato 24 12
Leopard Frog 26 13
Apple 34 17
Human 46 23
Chimpanzee 48 24
Dog 78 39
Adder’s tongue fern
1260
630
Section 10.2 Summary – pages

11. In Humans, how many chromosomes would each of these cells have…..
CHEEK CELL 46
SPERM CELL 23
EGG CELL 23
NERVE CELL 46

12. ● Body cells are made by the division process MITOSIS.
Since they have different amounts of chromosomes, the way they are made differ.
● Body cells are made by the division process MITOSIS.
● Sex cells are made by the division process MEIOSIS.

13. The cell cycle (or entire life cycle of the cell) consists of:
Before a cell can divide by either method, it must first prepare for cell division.
The cell cycle (or entire life cycle of the cell) consists of:
INTERPHASE: The longest/busiest stage in a cell’s life
1. Chromosomes (DNA) replicates
2. Cell grows bigger
CELL DIVISION: Mitosis or Meiosis
CYTOKINESIS: When the cytoplasm divides and the cell completely separates.

14. Mitosis: cell division that makes BODY CELLS.46
It starts with a DIPLOID cell
Chromosomes Replicate 92 46 46
It ends with TWO IDENTICAL DIPLOID cells

15. PHASES OF MITOSIS (Paul Makes A Taco)
PROPHASE
Chromosomes coil up
Nuclear envelope disappears
Spindle fibers form
METAPHASE
Chromosomes Line up in the middle
Spindle attaches to chromosomes

16. PHASES OF MITOSIS (Paul Makes A Taco)
ANAPHASE
Chromosomes split and are pulled apart
TELOPHASE
Chromosomes uncoil
Nuclear envelopes reappear
Cell is splitting into two

17. Meiosis: cell division that makes SEX CELLS.46
It starts with a DIPLOID cell
Chromosomes Replicate 92 46 46 23 23 23 23
It ends with FOUR HAPLOID cells (not identical)

18. Section 10.2 Summary – pages 263-273
Meiosis
These haploid cells are called sex cells— gametes.
Male gametes are called sperm.
Female gametes are called eggs.
Section 10.2 Summary – pages

19. Section 10.2 Summary – pages 263-273
Meiosis
When a sperm fertilizes an egg, the resulting zygote once again has the diploid number of chromosomes.
Section 10.2 Summary – pages

20. Crossing-Over In Meiosis:
When homologous chromosomes actually break and exchange genetic material- is a process known as crossing over.

21. Crossing over causes variations in the alleles on each chromosome.

22. Section 10.2 Summary – pages 263-273
Nondisjunction
The failure of homologous chromosomes to separate properly during meiosis is called nondisjunction.
This would occur when homologous chromosomes are suppose to separate from each other.
Section 10.2 Summary – pages

23. Section 12.3 Summary – pages 323 - 329
This chart of chromosome pairs is called a karyotype, and it is valuable in identifying unusual chromosome numbers in cells.
Section 12.3 Summary – pages

24. Section 12.3 Summary – pages 323 - 329
Down syndrome: Trisomy 21
Down syndrome is the only autosomal trisomy in which affected individuals survive to adulthood.
Section 12.3 Summary – pages

25. Section 12.3 Summary – pages 323 - 329
Down syndrome: Trisomy 21
Extra chromosome on 21
• 1 in every 1100 live births
• Range from mild to severe physical and mental disabilities
The incidence of Down syndrome births is higher in older mothers, especially those over 40.
Section 12.3 Summary – pages

26. Section 12.3 Summary – pages 323 - 329
Abnormal numbers of sex chromosomes
Many abnormalities in the number of sex chromosomes are known to exist.
Any individual with at least one Y chromosome is a male, and any individual without a Y chromosome is a female.
Section 12.3 Summary – pages

27. Turners Syndrome Absence of one X chromosome
Occurs in 1 out of every 2,500 live female births.
Physical characteristics
No mental disability

28. Section 12.3 Summary – pages 323 - 329
Abnormal numbers of sex chromosomes
Most of these individuals lead normal lives, but they cannot have children and some have varying degrees of mental retardation.
XXX
“Trisomy X”
XXY
“Klinefelter’s”
XYY
“Jacob’s Syndrome”
Section 12.3 Summary – pages

29. Question 1 A. diploid B. haploid C. biploid D. polyploid
A cell with two of each kind of chromosome is __________.
A. diploid
B. haploid
C. biploid
D. polyploid
Section 2 Check

30. Homologous Chromosome 4
The answer is A. The two chromosomes of each pair in a diploid cell are called homologous chromosomes. Each has genes for the same traits. a A
Terminal
Axial
Inflated D d
Constricted T t
Short
Tall
Section 2 Check

31. Mitosis and Development
Question 2
Meiosis
What is the importance of meiosis in sexual reproduction?
Haploid gametes
(n=23)
Sperm Cell
Meiosis
Egg Cell
Fertilization
Diploid zygote
(2n=46)
Multicellular
diploid adults
(2n=46)
Mitosis and Development
Section 2 Check

32. Mitosis and Development
Meiosis is cell division that produces haploid gametes. If meiosis did not occur, each generation would have twice as many chromosomes as the preceding generation.
Meiosis
Haploid gametes
(n=23)
Sperm Cell
Meiosis
Egg Cell
Fertilization
Diploid zygote
(2n=46)
Multicellular
diploid adults
(2n=46)
Mitosis and Development
Section 2 Check

33. Question 2 A. polygenic inheritance B. incomplete dominance
Trisomy usually results from _______.
(TX Obj 2; 6C)
A. polygenic inheritance
B. incomplete dominance
C. nondisjunction
D. twenty-two pairs of chromosomes
The answer is C.
Section 3 Check