1. The Cellular Basis of Inheritance
Chapter 9
The Cellular Basis of Inheritance

2. Reproduction
Asexual – process in which a single cell or set of cells produces offspring that inherit all their genetic material from one parent
Ex. Binary fission – bacteria
Sexual – process in which genetic material from two parents combines and produces offspring that differ genetically from either parent
Fertilization – egg fuses with sperm (zygote)
Cellular division – division of the genetic material of a cell in which two new cells are created

3. Chromosome Structure Nucleus – control center of cell Contains DNA
Chromatin – thin fibers of protein and DNA found in a non-dividing cell
Chromosomes – Condensed, coiled, chromatin, that forms in dividing cells
Chromatid (sister) – each half of a duplicated chromosome
Centromere – Site of attachment for chromatids

4. Chromosome Structure

5. Chromosome Numbers
Each species has a characteristic number of chromosomes
Humans – 46, 23 pairs
Fruit Flies – 8
Chimps – 48
Carrot - 18

6. Chromosome Numbers Male XY Female XX Humans
Sex Chromosomes (2) Determine the sex
Male XY
Female XX
Autosomal Chromosomes (44)

7. Chromosome Numbers
Homologous Chromosomes – One of a pair of morphologically similar chromosomes (mother, father)
Carry genes for the same traits
Karyotype – a technique for examining the chromosome makeup of an individual

8. Chromosome Numbers Somatic cells – body cells
Diploid (2N)
Cells that contains 2 of each type of chromosome
Somatic cells – body cells
Haploid (1N)
Cells that contain only 1 set of chromosomes
Germ cells – those that give rise to gametes

9. Cell Cycle
Cell Cycle
Sequence of events from the production of a eukaryotic cell to the time the cell itself reproduces
Three Stages in the cell cycle
Interphase
Mitosis
Cytokinesis

11. Cell Cycle
Interphase
Period of cell growth and development before cell division (90% cells life)
3 Phases of Interphase
G1 – Time of cell growth
S – Cells DNA is copied (replicated)
G2 – Cell prepares for division

12. Cell Cycle
Mitosis
Cell (nuclear) division in which the number of chromosomes is kept the same from parent cells to daughter cells
2N parent cell creates 2 diploid daughter cells
4 stages of Mitosis
Prophase
Metaphase
Anaphase
Telophase

13. Cell Cycle Mitosis Spindle – football shaped framework of microtubules
Prophase
1. Each duplicated chromosome (consisting of two sister chromatids) condenses from thread-like form to rod-like form
2. Nuclear envelope and nucleolus disappear
3. Centrosomes form and move to opposite ends of the cell and give rise to spindle fibers
Spindle – football shaped framework of microtubules

15. Cell Cycle
Mitosis
Metaphase (midway between)
Spindle fibers (microtubules) attach to the centromeres of the chromosomes and align them in the center of the cell (spindle equator)

17. Cell Cycle
Mitosis
Anaphase
Sister chromatids of each chromosome separate and move to opposite poles
Each chromatid is now its own “daughter” chromosome

19. Cell Cycle 1. Chromosomes return to threadlike form
Mitosis
Telophase
1. Chromosomes return to threadlike form
2. Nuclear envelopes begin to reform and separate the 2 new sets of chromosomes
3. Spindle fibers disassemble
4. Nucleolus forms in each of the newly forming cells

21. Cell Cycle Cytokinesis Division of the cytoplasm
Splitting of a parent cell into daughter cells
Plants
Cell plate – vesicles containing cell wall building substances fuse together and separate the two new cells
Animals
Cleavage furrow – area of cell membrane that pinches inward until 2 new cells are formed

24. Mitosis Video Clip

25. Meiosis
Meiosis
Cell (nuclear) division in which the chromosome number is cut in half
2N cell divides to form 4 (1N) cells
Two cell divisions – 2 stages
Meiosis I
Prophase I, Metaphase I, Anaphase I, Telophase I
Meiosis II
Prophase II, Metaphase II, Anaphase II, Telophase II

26. Meiosis Prophase I 1. Chromosomes condense to rod-like form
2. Nucleolus and nuclear membrane disappear
3. Centrosomes form and move to poles, give rise to spindle fibers
4. Homologous chromosomes pair up creating a tetrad (4 chromatids)
Crossing over – part of chromatid may break off and attach to adjacent chromatid on the homologous chromosome
Genetic recombination – regrouping of genes due to an exchange of maternal and paternal genetic material

28. Meiosis
Metaphase I
Spindle fibers attach to the centromeres, and homologous pairs line up side by side (tetrad) on the spindle equator

30. Meiosis
Anaphase I
Homologous chromosomes are separated and moved to opposite poles

32. Meiosis
Telophase I
Cytokinesis occurs and produces 2 haploid (1N) cells
Each new cell contains one chromosome from each homologous pair

34. Meiosis
Prophase II
Spindle fibers form and attach themselves to the centromeres of the chromosomes

36. Meiosis
Metaphase II
Chromosomes are moved to the equator of the cell

38. Meiosis
Anaphase II
Chromatids separate and move toward opposite poles of the cell

40. Meiosis Gametes (sperm, egg) Telophase II 4 daughter nuclei
Each cell has a haploid chromosome number and all are in the unduplicated state
Gametes (sperm, egg)

42. Meiosis Video Clip