Patterns of Chromosome Inheritance
Cancer
Patterns of Genetic Inheritance
DNA Biology and Technology
Patterns of Chromosome Inheritance
Humans have 46 chromosomes that occur in 23 pairs. 22 of the pairs are called autosomes, one pair is the sex chromosome. Males have the XY chromosome and females the XX. Chromosomes are visible in all cells of the body barring red blood cells. A computer display of the chromosomes is called a karyotype.
cancergenome.nih.gov/
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The cell cycle is an orderly process composed of 2 parts: interphase and cell division. Most of the cell cycle is spent in interphase. During this time, organelles carry on their usual function. The cell also gets ready to divide and as it grows larger, the number of organelles doubles as does the amount of chromatin and DNA synthesis occurs. DNA synthesis permits interphase to be divided into 3 stages: G1, S, and G2. - G1- A cell doubles its organelles and accumulates the material needed for DNA synthesis
- S- DNA replication occurs, resulting in duplicated chromosomes
- G2- The cell synthesizes proteins needed for cell division
- M- the sister chromatids separate becoming chromosomes w/2 daughter nuclei
- Cytokinesis- 2 daughter cells present
Mitosis is duplication division. The dividing cell is the parent cell, the new cells are called the daughter cells. They are genetically identical. During mitosis, chromatin in the nucleus becomes highly condensed and the chromosomes become visible. The sister chromatids are held together by the centromere. After the centromeres split, the sister chromatids separate.
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An important event of mitosis is the duplication of the centrosome, the microtubule organizing the center of the cell. After they separate, the form the poles of the miotic spindle, where the centrosomes assemble the microtubules that make up the spindle fibers. The chromosomes are attached to the fibers by the centromere. An array of microtubules is called an aster. Centrioles are short cylinders of microtubules present in centrosomes.There are four phases of mitosis: prophase, metaphase, anaphase, and telophase. Although they appear as four separate stages, they are one continous, fluid phase without interruption.
- Prophase- centrosomes have duplicated and the nucleolus has disappeared, duplicated chromosomes are visible
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- Metaphase- each chromatid is attaced to a spindle fiber, cetromeres of the duplicated chromosomes are aligned with equator
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- Anaphase- sister chromatids part and become daughter chromosomes that move toward spindle poles
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- Telophase- daughter cells are forming as nuclear envelopes and nucleoli reappear
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Cytokinesis is the division of the cytoplasm and organelles. In human cells, a slight indentation, the cleavage furrow, passes around the circumference of the cell. Actin filaments form a contractile ring and the cleavage furrow pinches the cell in half. Each cell becomes enclosed by its own plasma membrane.
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Meiosis is reduction division. Because meiosis involves two divisions, there are 4 daughter cells. Each daughter cell has 1 of each kind of chromosome, therefore half as many as the parent cell. The parent cell is diploid (2n) and the daughter cell haploid (n.) Daughter cells which result from meiosis are gametes.
At the start of meiosis there are 2 chromosome pairs which are homologues. The 2 cell divisions of meiosis are broken into meiosis I and meiosis II. Prior to meiosis I, DNA replication has occurred. During meiosis I, The homologous chromosomes line up side by side, called synapsis. The period between meiosis I and II is called interkinesis.
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At the start of meiosis there are 2 chromosome pairs which are homologues. The 2 cell divisions of meiosis are broken into meiosis I and meiosis II. Prior to meiosis I, DNA replication has occurred. During meiosis I, The homologous chromosomes line up side by side, called synapsis. The period between meiosis I and II is called interkinesis.
- Meiosis I- duplicated homologous pairs synapse and separate
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- Meiosis II- sister chromatids separate becoming daughter chromosomes
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In humans, daughter cells mature into gametes or sex cells that fuse during fertilization. Fertilization restores the haploid number to a diploid number in the zygote, the first cell of a new individual. Meiosis I and II are broken down into four stages each meiosis I stages with a I and meiosis II stages with a II. Here we discuss meiosis I stages:
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- Prophase I- synapsis and crossing over occur
- Metaphase I- homologous pairs align independently at equator
- Anaphase I- homologous chromosomes separate and move toward poles
- Telophase I- daughter cells are forming and will divide again
www.accessexcellence.org/.
Meiosis is a part of spermatogenesis, the production of sperm in males and oogenesis, the production of eggs in females.
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An individual may be born with too few or too many autosomes or sex chromosomes. This is usually due to nondisjunction during meiosis. If nondisjunction occurs, a person could have trisomy, one type of chromosome present in 3 copies, or monosomy, one type of chromosome is present in a single copy. The most common autosomal trisomy is Down Syndrome, or trisomy 21.
fig.cox.miami.edu/~cmallery/
An individual may be born with too few or too many autosomes or sex chromosomes. This is usually due to nondisjunction during meiosis. If nondisjunction occurs, a person could have trisomy, one type of chromosome present in 3 copies, or monosomy, one type of chromosome is present in a single copy. The most common autosomal trisomy is Down Syndrome, or trisomy 21.
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Changes in the number of sex chromosomes also result in various sydromes. With Turner Syndrome, an individual has only one sex chromsome, an X. In Klinefelter Sydrome, a male has 2 X chromosomes and 1 Y chromosome. Some females have more than 2 X chromosomes and extra Barr bodies in the nucleus. They are referred to as Poly-X females. Jacobs Syndrome results from a chromosome pattern of XYY.
Changes in chromosome structure are another type of chromosomal mutation.
Cancer
Cancer encompasses over a hundred different diseases, although differing in type, they have common characteristics.
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Cancer is a genetic disease due to mutations on two types of genes: the proto-oncogenes and the tumor-supressing genes. When a proto-oncogenes mutate they become cancer-causing oncogenes. Whatever a proto-oncogene does an oncogene does better. When tumor-supressor genes mutate, they no longer inhibit the cell cycle and promote apoptosis.
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Oncology is the study of cancer. Tumors are classified to their place of origin. Carcinomas are cancers of the epithelial tissues and adenocarcinomas are cancers of the glandular epithelial cells. Sarcomas are cancers of muscle, bone, and connective tissues. Leukemias are cancers of the blood and lymphomas cancers of the lymphatic tissue. Patterns of cancer development have shown that there are genetic and environmental risk factors for cancers as well as some guidelines that may prevent cancer:
Causes of cancer:
There are routine screening tests for cancer and self examination, along with regular check ups and blood work from a doctor, prove invaluable. Genetic testing is also available.
The treatment of cancer has evolved, but there are standard therapies in use:
Pattern of Genetic Inheritance
A genotype refers to the genes of an individual. Alternative forms of a gene having a different locus on a pair of chromosomes and affecting the same trait are alleles. It is customary to designate an allele by a letter which represents a specific trait. A dominant allele is assigned uppercase and a recessive allele lowercase. Alleles occur in pairs and normally an individual has 2 alleles for each trait. A person with 2 dominant alleles has a homozygous dominant genotype. A person with 2 recessive alleles has a homozygous recessive recessive genotype. A person with one of each has a heterozygous genotype. The genotype refers to the genes, the phenotype to the trait or characteristic.
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During gametogenesis, the chromosome number is reduced. A chromosome has 46, a gamete 23. This occurs as a result of meiosis. A monohybrid is an individual that is heterozygous to one pair of alleles. The Punnett sqaure is a tool which helps determine the outcome of genotypes/phenotypes. The genotypic ratio is 1:2:1 and the phenotypic ratio 1:3:1.
A dihybrid cross can form four pair of possible types of gametes. The dihybrid phenotypic ratio is 9:3:3:1.
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Changes in chromosome structure are another type of chromosomal mutation.
- Deletion- occurs when an end of a chromosome breaks off or when 2 simultaneous breaks lead to the loss of an internal segment
- Duplication- the presence of a chromosomal segment more than once n the same chromosome
- Inversion- a segment of the chromosome is turned around 180 degrees
- Translocation- a movement in the chromosome segment from one chromosome to antother nonhomologous chromosome
Cancer
Cancer encompasses over a hundred different diseases, although differing in type, they have common characteristics.
- Lack differentiation
- Have abnormal nuclei and fail to undergo apoptosis
- Have unlimited replicative potential due to telomerase
- Form tumors
- No need for growth factors and do not respond to inhibitory growth factors
- Gradually become abnormal through a multistage process of initiation, promotion and progression
- Undergo angiogenesis ( the formation of new blood vessels) and metastasis (cells that begin new tumors far from the primary tumor)
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Cancer is a genetic disease due to mutations on two types of genes: the proto-oncogenes and the tumor-supressing genes. When a proto-oncogenes mutate they become cancer-causing oncogenes. Whatever a proto-oncogene does an oncogene does better. When tumor-supressor genes mutate, they no longer inhibit the cell cycle and promote apoptosis.
www.healthofchildren.com/
Oncology is the study of cancer. Tumors are classified to their place of origin. Carcinomas are cancers of the epithelial tissues and adenocarcinomas are cancers of the glandular epithelial cells. Sarcomas are cancers of muscle, bone, and connective tissues. Leukemias are cancers of the blood and lymphomas cancers of the lymphatic tissue. Patterns of cancer development have shown that there are genetic and environmental risk factors for cancers as well as some guidelines that may prevent cancer:
Causes of cancer:
- Hereditary
- Mutagens- an agent which causes mutation
- Carcinogens- a chemical which causes cancer
- Radiation- UV light, radon gas, nuclear fuel/waste, X-rays
- Organic chemicals- tobacco smoke, pollutants
- Viruses- Hep B & C, Epstein-Barr virus, HPV
- Dietary choices- avoid nitrite cure food, avoid obesity and high fat foods
- Don't smoke or chew
- Don't sunbathe
- Avoid alcohol
- Avoid radiation
- Get tested for cancer
- Avoid exposure to occupational hazards
- Awareness of hormone replacement therapy
- Vaccines
- Diet which consists of high fiber foods, antioxidents, vegetables
There are routine screening tests for cancer and self examination, along with regular check ups and blood work from a doctor, prove invaluable. Genetic testing is also available.
The treatment of cancer has evolved, but there are standard therapies in use:
- Surgery
- Radiation
- Chemotherapy, sometimes in conjunction with bone marrow transplants
Pattern of Genetic Inheritance
A genotype refers to the genes of an individual. Alternative forms of a gene having a different locus on a pair of chromosomes and affecting the same trait are alleles. It is customary to designate an allele by a letter which represents a specific trait. A dominant allele is assigned uppercase and a recessive allele lowercase. Alleles occur in pairs and normally an individual has 2 alleles for each trait. A person with 2 dominant alleles has a homozygous dominant genotype. A person with 2 recessive alleles has a homozygous recessive recessive genotype. A person with one of each has a heterozygous genotype. The genotype refers to the genes, the phenotype to the trait or characteristic.
ghs.gresham.k12.or.us/.../
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Two trait crosses are a bit more complex and more combinations are possible due to the fact that a gamete will receive one short and one long chromosome of either color (paternal and maternal chromosomes.) Homologues separate independently and it does not matter which member of a pair goes into which gamete.A dihybrid cross can form four pair of possible types of gametes. The dihybrid phenotypic ratio is 9:3:3:1.
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Genetic disorders can be autosomal dominant: an individual with the alleles AA or Aa will have the disorder, or autosomal recessive: an individual with the alleles aa will have the disorder. Some of the more common autosomal recessive disorders are:
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- Tay-sachs- lack of the enzyme hexosaminidase A (Hex A) and the storage of the substrate glycosphingolipid in lysomes
- Cystic Fibosis- chloride ions fail to pass through a plasma membrane channel protein in cells, which interferes with the function of the lungs and pancreas
- Phenylketonuria (PKU)- affects the nervous system development due to a lack of the enzyme phenylalanine
- Sickle Cell- the red blood cells are not bi-concave disks and have an irregular shape causing anemia, poor circulation, and low resistance to infection
- Marfan Syndrome- a defect in an elastic connective tissue protein called fibrillin
- Huntinton Disease- a neurological disorder that leads to the degeneration of brain cells caused by a mutated copy of the gene for protein, huntintin
courses.bio.psu.edu/.../
Incomplete dominance occurs when the heterozygote is intermediate between the two homozygotes. Codominance occurs when alleles are equally expressed in a heterozygote. When traits are controlled by multiple alleles the gene exists in in several allelic forms.
Males and females have 23 pairs of chromosomes, 22 are autosomes, 1 is the sex chromosome. Traits controlled by the genes on the sex chromosome are sex-linked: an allele on the X chromosome is X-linked, an allele on the Y, Y-linked. Most sex-linked disorders are carried on the X chromosome.
Some X-linked recessive disorders are:
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DNA Biology and Technology
DNA is the genetic material and found in the chromosomes. Genetic material must be able to do 3 things: replicate so it can be transmitted to the next generation, store information, and undergo mutations that provide genetic variability.
DNA is a double helix, composed of 2 strands that spiral around each other. Each strand is a polynucleotide, because it is composed fo a series of nucleotides: a molecule composed of 3 subunits- phosphoric acid (phosphate), a pentose sugar (deoxyribose), and a nitrogen-containing base. The bases of the structure are held together by complementary paired bases. The bases are important to the functioning of DNA and are paired as follows: the purines, Adenine (A) or Guasine (G) with the pyrimidines, Thymine (T) and cytosine (C). The 2 strands of DNA run anti-parallel, or opposite directions.
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The process of copying the DNA helis is called DNA replication. During replication, the double-strand structure allows each origianl strand to serve as a template for the formation of a new complementary strand. Rarely, a mutation may occur, causing the sequence of the bases in the new strand different from the parental strand. Usually the error is fixed by enzymes, but that is not always the case.
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Males and females have 23 pairs of chromosomes, 22 are autosomes, 1 is the sex chromosome. Traits controlled by the genes on the sex chromosome are sex-linked: an allele on the X chromosome is X-linked, an allele on the Y, Y-linked. Most sex-linked disorders are carried on the X chromosome.
Some X-linked recessive disorders are:
- Color blindness
- Muscular Dystrophy
- Hemophilia
www.merck.com/.../figures/
DNA Biology and Technology
DNA is the genetic material and found in the chromosomes. Genetic material must be able to do 3 things: replicate so it can be transmitted to the next generation, store information, and undergo mutations that provide genetic variability.
DNA is a double helix, composed of 2 strands that spiral around each other. Each strand is a polynucleotide, because it is composed fo a series of nucleotides: a molecule composed of 3 subunits- phosphoric acid (phosphate), a pentose sugar (deoxyribose), and a nitrogen-containing base. The bases of the structure are held together by complementary paired bases. The bases are important to the functioning of DNA and are paired as follows: the purines, Adenine (A) or Guasine (G) with the pyrimidines, Thymine (T) and cytosine (C). The 2 strands of DNA run anti-parallel, or opposite directions.
cache.eb.com/eb/
The process of copying the DNA helis is called DNA replication. During replication, the double-strand structure allows each origianl strand to serve as a template for the formation of a new complementary strand. Rarely, a mutation may occur, causing the sequence of the bases in the new strand different from the parental strand. Usually the error is fixed by enzymes, but that is not always the case.
faculty.uca.edu/~johnc/
RNA is made up of nucleotides containing the sugar ribose. The only difference nucleotide wise in RNA than DNA is that the base thymine (T) was replaced with uracil (U.) RNA is single stranded, but may double back on itself. Complementary base pairing still occurs.
Ribosomal RNA (rRNA) is produced in the nucleolus of a nucleus where a portion of DNA serves a template for its formation. rRNA joins with proteins made in the cytoplasm when protein synthesis is about to begin. Messenger RNA (mRNA) is produces in the nucleus where the DNA served a a template for its formation. mRNA carries genetic information from DNA to the ribosomes in the cytoplasm. Transfer RNA (tRNA) is produced in the nucleus and transfers amino acids are joined forming a protein.
DNA provides the cell with a blueprint for synthesizing the proteins. Proteins are composed of subunits called amino acids. 20 different amino acids are commonly found in the proteins, which are synthesized at the ribosomes. Proteins determine the structure and function of the various cells in the body.
The first step in gene expression is transcription: a strand of mRNA forms that is complimentary to a portion of DNA. Transcription means "faithful copy." The second step is translation. Translation means to put the information into a different language. In this case, a sequence of nucleotides is translated into the sequence of amino acids.
www.accessexcellence.org/RC/VL/GG/ecb/ecb_ima...
Ribosomal RNA (rRNA) is produced in the nucleolus of a nucleus where a portion of DNA serves a template for its formation. rRNA joins with proteins made in the cytoplasm when protein synthesis is about to begin. Messenger RNA (mRNA) is produces in the nucleus where the DNA served a a template for its formation. mRNA carries genetic information from DNA to the ribosomes in the cytoplasm. Transfer RNA (tRNA) is produced in the nucleus and transfers amino acids are joined forming a protein.
DNA provides the cell with a blueprint for synthesizing the proteins. Proteins are composed of subunits called amino acids. 20 different amino acids are commonly found in the proteins, which are synthesized at the ribosomes. Proteins determine the structure and function of the various cells in the body.
The first step in gene expression is transcription: a strand of mRNA forms that is complimentary to a portion of DNA. Transcription means "faithful copy." The second step is translation. Translation means to put the information into a different language. In this case, a sequence of nucleotides is translated into the sequence of amino acids.
www.accessexcellence.org/
Transcription begins when the enzyme RNA polymerase opens up the DNA helix just in front so that a complementary base pairing can occur. The RNA polymerase joins the RNA nucleotides and an mRNA molecule forms. The mRNA must be processed before entering the cytoplasm. The mRNA becomes mature mRNA. During translation, transfer RNA molecules bring amino acids to the ribosomes where polypeptide synthesis occurs. Polypeptide syntheis has 3 steps:
- Initiation- mRNA binds to the smaller of the 2 ribosomal units;then the larger subunit associates with the smaller one
- Elongation- the polypeptide lengthens one amino acid at a time, an incoming tRNA amino acid complex arrives at the A site and receives the peptide from the outgoing tRNA
- Termination- occurs at the codon that means stop and does not code for an amino acid, the ribosome dissociates into 2 subunits and falls off the mRNA molecule
All cells receive a copy of all genes, however they differ as to which genes are actively expressed. A variety of mechanisms regulate gene expression and they are grouped into four levels:
Functional genomics is the study of how the 25,000 different genes in the human genome function. Comparative genomics is a way to determine how species have evolved and how genes and noncoding regions of the genome function.
Protemics is the study of the structure, function, and interaction of cellular proteins. Bioinformatics is the application of computer programs to the study of the genome.
- Transcriptional control- in the nucleus, a number of mecnanisms regulate which genes are transcribed and the rate at which transcription occurs
- Posttranscriptional control- occurs in the nucleus after DNA is transcribed adn mRNA is formed
- Translational control- occurs in the cytoplasm after the mRNA leaves the nucleus adn before there is a protein product
- Posttranslational control- occurs in the cytoplasm after protein synthesis
Functional genomics is the study of how the 25,000 different genes in the human genome function. Comparative genomics is a way to determine how species have evolved and how genes and noncoding regions of the genome function.
Protemics is the study of the structure, function, and interaction of cellular proteins. Bioinformatics is the application of computer programs to the study of the genome.
Citations:
Biology Project: Cell Biology. (2008) http://www.biology.arizona.edu/CELL_BIO/cell_bio.html
Folding @ Home Distributed Computing. (2008) http://folding.stanford.edu/English/Science
Hyperphysics:Chemical Bonding. (2008) http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html
Mader, S. (2008) Exploring Life and Science, Chemistry of Life, Cell Structure and Function, and
Regulation and Organization of Body Systems. Human Biology, 10th ed. (p 1-84)
Microbiology. (2008) http://www.scienceprofonline.org/
Folding @ Home Distributed Computing. (2008) http://folding.stanford.edu/English/Science
Hyperphysics:Chemical Bonding. (2008) http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html
Mader, S. (2008) Exploring Life and Science, Chemistry of Life, Cell Structure and Function, and
Regulation and Organization of Body Systems. Human Biology, 10th ed. (p 1-84)
Microbiology. (2008) http://www.scienceprofonline.org/
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