chapter 6 chromosomes and cell reproduction
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Chapter 6- Chromosomes and Cell Reproduction

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Chapter 6- Chromosomes and Cell Reproduction. I. Chromosomes. A. New cells are formed by cell division. 1. An adult human body produces about 2 trillion cells EVERY day! This is about 25 million new cells per second! 2. Cell division allows for this.

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a new cells are formed by cell division
A. New cells are formed by cell division.

1.An adult human body produces about 2 trillion cells EVERY day! This is about 25 million new cells per second!

  • 2.Cell division allows for this.
  • 3.Eukaryotic organisms undergoing growth, development, repair, or asexual reproduction divide by a different type of cell division.
  • 4. Gametes are reproductive cells (egg and sperm) undergo meiosis for cellular division.
b bacterial cells divide to reproduce
B. Bacterial cells divide to reproduce

1.Bacteria reproduce by a type of cell division called binary fission.

  • 2.Binary fission is a form of asexual reproduction that produces identical offspring.

3. In asexual reproduction a single parent passes exact copies of its entire DNA to its offspring.

c eukaryotic cells form chromosomes before cell division
C. Eukaryotic cells form chromosomes before cell division
  • 1.A gene is a segment of DNA that codes for a protein or RNA molecule.

2. As a Eukaryotic cell prepares to divide, the DNA and the proteins associated with DNA coil into a structure called chromosomes.

  • 3. Chromosomes are squished together called chromatids.

4. The chromosome has two strands – one from mom and one from dad. A “twist tie” called a centromere holds them together. See page 119.

d chromosome number and structure affect development
D. Chromosome number and structure affect development.
  • 1.Each human somatic (any cell besides sex cells) normally contain two copies of 23 chromosomes for a total of 46 chromosomes.
  • 2.Each chromosome contains thousands of genes that play important roles in determining how a person’s body develops and functions.
  • 3. Each of the 23 pairs of chromosomes consists of two homologous chromosomes.
  • 4. Homologous chromosomes are chromosomes that are similar in size, shape and genetic content.
  • 5. All of the cells in the body, besides gametes have two pairs of chromosomes. (One from mom one from dad) they are called diploid.
  • 6. Sex cells only have DO NOT have a pair, they are called haploid (1/2 the amount of chromosomes)

7. A zygote is a fertilized egg cell.

  • 8. Look at figure 6-1 pages 121 to view number of chromosomes.
e chromosomes determine your sex
E. Chromosomes determine your sex.
  • 1.Of the 23 pairs of chromosomes in human somatic cells, 22 pairs are called autosomes
  • 2.Autosomes are chromosomes that are not directly involved in determining the sex of an individual.
  • 3.The sex chromosomes, one of the 23 pairs contain the gene that determines the gender. Males determine the gender of the human.
f change in chromosome number
F. Change in chromosome number
  • 1.Sometimes a human could have different chromosome numbers.
  • 2.A karyotype is performed to view an individual’s chromosomes.
  • 3.Down syndrome is an extra copy on pair 21.
ii the cell cycle
II. The cell Cycle

A. The cell cycle describes the life of a Eukaryotic cell.

  • 1.The cell cycle is a repeating sequence of cellular growth and division during the life of an organism.
  • 2.A cell spends 90% of its time in the first three phases of the cycle-interphase.
  • 3. First growth (G1)phase- a cell grows rapidly and carries out its routine functions. Cells that are not dividing remain in the G1 phase.

4. Synthesis (S) phase- A cell’s DNA is copied during this phase. At the end of this phase, each chromosome consists of two chromatids attached at the centromere.

  • 5. Second growth (G2) phase-In the G2 phase, preparations are made for the nucleus to divide.

6. Mitosis-the process during cell division in which the nucleus of a cell is divided into two nuclei.

  • 7. Each nucleus ends up with the same number and kinds of chromosomes as the original cell.

8. Cytokinesis-the cytoplasm splits.

b the cell cylce is carefully controlled
B. The cell cylce is carefully controlled
  • 1.If a cell spends 90% of its time in interphase how do cells “know” when to divide?
  • 2.Cell Growth (G1) checkpoint-This checkpoint makes the key decision of weather the cell will divide or not.
  • 3. DNA synthesis (G2) checkpoint-DNA replication is checked at this point by DNA repair enzymes. If this checkpoint is passed, proteins help to trigger mitosis.
  • 4. Mitosis checkpoint-will trigger the exit from mitosis.
c when control is lost cancer
C. When control is lost: cancer
  • 1.Certain genes contain the information necessary to make the proteins that regulate cell growth and division.
  • 2.If one of these genes is mutated, the protein may not function.
  • 3. Cancer is the uncontrolled growth of cells.
  • 4. Cancer is a disorder of cell division.
d mitosis
D. Mitosis
  • I Prefer Mangos And Tangerines

Interphase (not really a phase)






  • Interphase- is part of the cell cycle before mitosis. During Interphase
        • The cell grows
        • DNA is being copied
        • This period between cell division can be very long.
  • Prophase- This is the longest phase. During this phase;
      • The nuclear envelope disappears.
      • The centrioles start to move to the opposite poles.
      • Spindle fibers start to form.
      • Chromosomes are becoming evident.
  • Metaphase-Metaphase is the shortest phase of mitosis.
      • The chromosomes line up in the middle of the cell.
  • ANAPHASE- Begins when the centromere that join the sister chromatids start to split.
      • The chromosomes are being pulled to the opposite sides of the cell toward the Centrioles.
  • TELOPHASE-Final process of mitosis.
      • Chromosomes are at the opposite poles.
      • Nuclear envelope reforms.
teacher note
Teacher note: