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. 3. Eukaryotic organisms undergoing growth, development, repair, or asexual reproduction divide by a different type of cell division.

Continued 4. Gametes are reproductive cells (egg and sperm) undergo meiosis for cellular division.

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 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.

Continued 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.

Centromere

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.

Continued 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.

Continued 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)

Continued 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. 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 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 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.

Continued 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.

Contined 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.

Continued 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 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.

Continued 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 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.

Continued 3. Cancer is the uncontrolled growth of cells. 4. Cancer is a disorder of cell division.

D. Mitosis I Prefer Mangos And Tangerines Interphase (not really a phase) Prophase Metaphase Anaphase Telophase Cytokinesis

INTERPHASE 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.

INTERPHASE

PROPHASE 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.

PROPHASE

METAPHASE Metaphase-Metaphase is the shortest phase of mitosis. The chromosomes line up in the middle of the cell.

METAPHASE

ANAPHASE 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.

ANAPHASE

TELOPHASE TELOPHASE-Final process of mitosis. Chromosomes are at the opposite poles. Nuclear envelope reforms.

TELOPHASE

CYTOKINESIS-Splitting of the cytoplasm.

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