Wednesday, June 11, 2008

Compendium Review Unit 1 Major Topic: Genetics

A. Chromosomes and the Cell Cycle

1. Humans - 46 chromosomes, 23 pairs
2. Karyotype - total view of all 23 pairs
3. 1 pair is sex chromosomes
4. The cell cycle
a. interphase (G1, S, G2 stages) normal functions, getting ready to divide, DNA synthesis
b. cell division - mitosis and cytokinesis
From the text, figures 18.1, showing the karyotype of a male, and 18.2 illustrating the cell cycle.B. Mitosis (for growth, replacement, repair; constant)
1. Prophase
a. chromosomes condense, visible
b. nuclear envelope fragments
c. nucleolus disappears
d. centrosomes move to opposite ends the nucleus
e. spindle fibers appear and attach to centromere
2. Metaphase
a. chromosomes line up along equator of the cell
b. fully formed spindle
3. Anaphase
a. centromeres split
b. sister chromatids separate (now chromosomes)
c. chromosomes move toward opposite poles of spindle
4. Telophase
a. chromosomes arrive at poles
b. chromosomes -> indistinct chromatin
c. spindle disappears
d. nucleoli reappear
e. nuclear envelope reassembles
5. Cytokinesis (split - cytoplasm & organelles, cleavage furrow)
Figure 18.3 from the text provides a nice overview of mitosis.
C. Meiosis (haploid gametes, 2 nuclear divisions)
1. Meiosis I (prophase I, metaphase I, anaphase I, telophase I)
a. synapsis and crossing-over - prophase I
b. homologous pairs align independently at equator - metaphase I
c. homologous pairs separate - anaphase I
c. 2 haploid daughter cells - telophase I
2. Meiosis II (prophase II, metaphase II, anaphase II, telophase II)
Figure 18.7 from the text provides a nice overview of meiosis.
D. Spermatogeneis (production of sperm in males)
1. Primary spermatocyte 2n(meiosis I)
2. 2 secondary spermatocytes n (meiosis II)
3. 4 spermatids n
4. After puberty, continual, 300k / min
E. Oogenesis (production of egg in females - meiosis and maturation)
1. Primary oocyte 2n (meiosis I)
2. Secondary oocyte n and first polar body n
3. Secondary oocyte stops meiosis II at metaphase II
4. Travels to oviduct, completes meiosis II only if fertilized
F. Fertilization
1. Steps
a. sperm swims with flagellum
b. only 1 sperm enters egg,
c. only sperm nucleus fuses with egg nucleus (cytoplasm and organelles from mother)
G. Pre-Embryonic and Embryonic Development
1. Processes of development (cleavage, growth, morphogenesis, differentiation)
2. Extraembryonic membranes (chorion, placenta, allantois, yolk sac, amnion)
3. Stages of development (fertilization to birth)
a. pre-embryonic development (fertilization to appearance of chorion)
b. embryonic development (implantation to eighth week)
Figure 17.3 from the text illustrates pre-embryonic development. Figure 17.4 illustrates embryonic development.
G. Chromosome inheritance
1. Trisomy, monosomy caused by nondisjunction
2. Down Syndrome - autosomal trisomy
3. Changes in sex chromosome #s - Turner, Klinefelter, Jacobs, Poly-X Female
4. Changes in chromosome structure
a. deletion - Williams syndrome, Cri du chat (cat's cry)
b. duplication
c. inversion
d. translocation - Alagille syndrome
A. Cancer Cells

1. Characteristics
a. lack differentiation (not specialized - epithelial, muscle, nervous, connective)
b. have abnormal nuclei
c. have unlimited ability to divide (telomerase gene turned on)
d. form tumors (no contact inhibition)
e. divide without growth hormones
f. become abnormal gradually (carcinogenesis)
g. undergo angiogenesis and metastasis
2. Cancer is genetic
a. proto-oncogenes become oncogenes
b. tumor-suppressor genes become inactive
3. Types of Cancer (see definition page - sarcomas, lymphomas, carcinomas)
Figure 19.2 illustrates the progression of the tumor.B. Causes
1. Heredity - BRCA1, BRCA2, RET, RB
2. Environmental carcinogens
a. radiation - UV light, X-rays, radon gas
b. organic chemicals - tobacco smoke, pollutants
c. viruses - HepB & C, Epstein-Barr, human papillomavirus
C. Diagnosis
1. Seven warning signs
a. Change in bowel or bladder habits
b. A sore that does not heal
c. Unusual bleeding or discharge
d. Thickening or lump in breast or elsewhere
e. Indigestion or difficulty swallowing
f. Obvious change in wart or mole (ABCD)
g. Nagging cough or hoarseness
2. Routine screening
a. Self-exam (breast and testicle)
b. Colonoscopy
c. Mammogram
d. Pap smear
e. PSA
3. Tumor marker tests - blood tests for tumor antigens/antibodies
4. Genetic - test for mutations in proto-oncogenes and tumor-suppressor genes
The image below shows the crystal structure of the human hepatitis B virus capsid. The reference can be found here.D. Treatment
1. Standard therapies
a. surgery
b. radiation - localized therapy, causes chromosomal breakage, disrupts cell cycle
c. chemotherapy - treats the whole body, damages DNA, interferes with DNA synthesis
d. bone marrow transplant
2. New therapies
a. immunotherapy
b. p53 gene therapy
A. Genotype and Phenotype
1. Genotype - genese of an idividual
2. Phenotype - visible expression of a genotype
B. One- and Two-Trait Inheritance
1. Forming the gametes
a. gametes carry half the chromosomes
b. gametes carry allele for each trait
2. One-trait crosses (Punnett square, genotypic and phenotypic ratios, probability)
3. Two-trait crosses (dihybrid cross, probability)
4. Family pedigrees for genetic disorders
5. Genetic disorders of interest
a. Autosomal recessive (Tay-Sachs, CF, phenylketonuria, sickle-cell disease)
b. Autosomal dominant (Marfan syndrome, Huntington disease)
Figure 20.6 from the text shows the resulting offspring when crossing two dihybrids. C. Beyond Simple Inheritance Patterns
1. Polygenic inheritance (polygenic traits=>continuous variation of phenotypes)
a. dominant allele codes for a product
b. skin color
c. multifactorial disorders - controlled by polygenes that are subject to environmental influences (Himalayan rabbits)
2. Incomplete dominance (wavy hair) and codominance (AB blood type)
3. Multiple allele inheritance (ABO blood types)
D. Sex-Linked Inheritance
1. X-linked alleles
a. in males, always inherited from mother
2. Pedigree for X-linked disorders
a. recessive disorders more often expressed in males b/c the Y chromosome lacks the allele
b. color blindness
c. muscular distrophy
d. hemophelia
Figure 20.18 from the text shows the pedigree for color blindness and lists ways in which to recognize a recessive X-linked disorder.IV. DNA BIOLOGY AND TECHNOLOGY
A. DNA and RNA Structure and Function
1. Structure of DNA
a. double helix
b. 2 backbones - sugar-phosphate
c. complementary base pairs = "ladder rungs" (purines=AG, pyrimidines=TC)
2. Replication of DNA
a. process of copying a DNA helix
b. double helix unwinds and unzips, each is a template (semiconservative)
c. complementary base pairing
d. 2 identical double helices produced
3. Structure and function of RNA (A,U,G,C)
a. rRNA - produced in nucleus, joins w/proteins to form subunits of ribosomes
b. mRNA - produced in nucleus, carries genetic info from DNA to ribosomes
c. tRNA - produced in nucleus, transfers amino acids to ribosomes
Figures 21.2 and 21.3 from the text show how, during replication, DNA is unzipped and new complementary bases of the nucleotides pair up to the old strand.
B. Gene Expression
1. Structure and function of proteins
a. made of 20 different proteins
b. determine structure and function of cells in our body
2. Transcription (nucleus)
a. section of DNA is template for production RNA molecule
b. resulting RNA has sequence of complementary bases and U takes the place of T
3. Translation (cytoplasm)
a. tRNA molecules contain anticodons, complementary to codons on mRNA
b. tRNA contains amino acid at other end
c. order of condons on mRNA dictate order of tRNA amino acids
d. occurs at ribosomes
4. Regulation of gene expression (not all genes on all the time)
a. transcriptional control - in nucleus, chromatin density and transcription factors
b. posttranscriptional control - in nucleus, mRNA processing
c. translational control - in cytoplasm, differential ability of mRNA to bind to ribosomes
d. posttranslational control - in cytoplasm, changes to the protein to make it functional
Figures 21.11 and 21.13 from the text illustrate the process of polypeptide synthesis and and overview of gene expression.
C. Genomics
1. The human genome has been sequenced - order of 3 billion base pairs, 25k genes
2. Functional and comparative genomics - how do our genes function, how do they compare to other species?
3. Proteomics and bioinformatics
4. A person's genome can be modified (ex-vivo & in-vivo gene therapy)
D. DNA Technology
1. Genes can be isolated and cloned (recombinant DNA)
2. Specific DNA sequences can be cloned (polymerase chain reaction)
3. Biotechnology products / genetic engineering
a. bacteria - insulin, human growth hormone, hepB vaccine
b. plants - insect and herbicide resistant, salt-tolerant plants
c. animals - bovine growth hormone, gene pharming, xenotransplantation
The photograph below is of Dolly, the first cloned mammal. I. PATTERNS OF CHROMOSOME INHERITANCE
Mitosis and meiosis - very similar, yet very different processes. To start, here is a fun animation along with a real life video that walks through the steps of mitosis. On the same website is an animation for meiosis. You can either play the video straight through or use the step buttons to walk through each phase. I am going to walk through a few of the differences between mitosis and meiosis. First, in meiosis, there are two nuclear divisions whereas in mitosis there is only one. That means that meiosis produces four daughter cells and mitosis produces only two. The four daughter cells from meiosis are haploid cells and the two daughter cells from mitosis are duploid. The daughter cells from meiosis are not genetically identical to the parent cell; they only have half the number of the parent cell. The daughter cells from mitosis are genetically identical to the parent cell. Meiosis occurs in sex cells and the purpose of it is to produce gametes. Mitosis occurs in automsomal cells and the purpose of it is for growth, for replacement and for repair. (Mader 2008)

Definitions for chapter 18 can be found here.

In 2005, cancer was the #2 leading cause of death in the US. With statistics like that, it seems like a no brainer - put into practice the recommended preventions of cancer. The text breaks down the list into two sections: Protective Behaviors and The Right Diet. A few behaviors one can change to help prevent cancer are to avoid smoke/smoking, avoid the sun and tanning beds, avoid alcohol and radiation, and be aware of occupational hazards. Many studies show that following a certain diet can also help in the prevention of cancer. Things like avoiding obesity, eating plenty of high-fiber foods, increasing consumption of foods rich in vitamins A & C, and including vegetables from the cabbage family in the diet. The American Cancer Society is a great resource for more information on prevention and detection.

Definitions for chapter 19 can be found here.

Sex-linked inheritance is different from autosomal inheritance in that male offspring only receive one allele for a given trait. That allele is passed to them from their mother. The Y chromosome that he received from his father does not carry an allele for that trait. In this way, males have a 50% chance of inheriting an X-linked recessive disorder if their mother is heterozygous. If he inherits the recessive allele from her, it will always express itself, since that is the only allele for that gene he will receive. The case is different for the daughter, who, without an affected father, has a zero percent chance of inheriting the disorder. She does, however, have a fifty percent chance of being a carrier. (Mader 2008)

Definitions for chapter 20 can be found here.

Transcription and translation. This is another area of biology that has me in complete amazement. The fact that we understand how our genes are copied and translated into proteins...the idea renders me speechless. And here it, my general overview. Transcription is the process by which a segment of RNA is made from a segment of DNA. The portion of the double helix that is to be transcribed unwinds and unzips so that the "ladder rungs" or bases are exposed. The exposed bases allow the complementary base pairs that will join to form RNA to line up in the correct order. RNA polymerase joins the nucleotides together to form RNA. rRNA, mRNA, and tRNA are all made in the nucleus in the same way. After production and processing, the 3 types of RNA move to the cytoplasm. mRNA finds the ribosomes (rRNA plus proteins) where translation occurs. Translation is the production of a polypeptide chain; the order of the amino acids in the chain is determined by the order of condons on mRNA. Codons are made up of three bases on mRNA. A codon of mRNA will only bind with the corresponding anticodon of tRNA. Each anticodon correlates to an amino acid that tRNA also carries. As mRNA moves through the ribosome, the codons pair with anticodons. The amino acid that was associated with that anticodon on tRNA gets added to the polypeptide chain. In this way, mRNA dictates the order of amino acids in a polypeptide chain.

Chapter 21 definitions can be found here.

Mader, Syliva S. Human Biology. New York, NY: McGraw-Hill (2008).

Links provided throughout the summary take you to online sources.

IMPORTANT NOTE: Any time "text" or "the text" is referenced in the above summary, I am referring to the textbook Human Biology by Sylvia Mader (cited directly above).

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