Module 3
Why can it seem that X-linked recessive diseases "skip" a generation?
Because the gene can be transmitted through carrier females.
Course Objectives
1. Identify the basic processes of cellular function. 2. Identify the basic structure and function of DNA, RNA, and chromosomes. 3. Describe DNA replication, transcription, translation, and mutation. 4. Compare and contrast chromosomal aberrations and selected associated diseases. 5. Describe modes of inheritance, including autosomal dominant, autosomal recessive, and X-linked inheritance, and name an example of a representative disease for each. 6. Construct a pedigree chart from inheritance data. 7. Describe the concepts of incidence and prevalence and how they relate to some common diseases. 8. Learn how risk factors impact a certain person's or population's chances of developing a certain disease process. 9. Discuss the basic concepts of multifactorial inheritance. 10. Understand the Threshold Model, recurrence risks, and transmission patterns for disease processes. 11. See how the environment in which a person is raised impacts certain genetic characteristics (nature vs. nurture). 12. Explore various diseases and the impact that both genes and environment have on these diseases.
What is meant by homologous chromosomes?
Homologous chromosomes are identical to each other, they are in pairs in 22 of the 23 chromosomes called autosomes.
How many does a normal human cell contain?
23 pairs, 46 individual chromosomes
What is meant by delayed onset of disease? What is an example of this?
Another kind of penetrance is age-dependent in which the symptoms of an inherited autosomal dominant disorder do not appear until later in life as is seen with Huntington chorea.
What is a carrier?
A carrier is an individual who has a disease causing allele but is phenotypically normal.
What is a karyotype?
A karyotype displays the pairs of chromosomes and their numbers. Abnormalities in the size and number of chromosomes can be identified.
What is mutation? What are some examples?
A mutation is an inherited alteration of genetic material. missense mutation: base pair substitution frameshift mutation: involves the insertion or deletion of one or more base pairs to the DNA molecule
What is meant by sex-limited and sex-influenced traits?
A sex limited trait is one that can occur in only one of the sexes often because of anatomic differences. Sex influenced traits is one that occurs much more often in one sex than in the other.
What do studies done with twins and people that were adopted show concerning the question of nature vs nurture? Review Table 5-3 on page 170.
Adoption studies have proven that even when children are taken out of the environment they shared with their birth parents, they are less likely to develop a certain disease. Prenatal influences cannot be discounted and may have long-lasting effects; if the children are older when adopted, the environmental influences have already taken hold; adoption agencies try to find adoptive parents that are similar to the birth parent Twin studies show how the links between genes and the environment: Monozygotic (MZ) twins are identical twins. Dizygotic (DZ) twins come from two different eggs and sperm. If both members of the twin pair share a trait, it is said to be concordant. If they do not share the trait, it is said to be discordant. Concordant rates differ by sex. The environment can make MZ twins even more similar.
What are the two common forms of aneuploidy?
Aneuploidy means that there are an abnormal number of chromosomes, usually 45 or 47 chromosomes instead of the normal 46.
What is cystic fibrosis, and how is it manifested clinically?
Autosomal recessive inheritance, consanguinity may be present. Lung disease, malnutrition, heart failure.
Schizophrenia is a severe emotional disorder characterized by delusions, hallucinations, bizarre behavior, and withdrawal from reality. The risk for developing schizophrenia increases for every first-degree relative who has the disease. If someone has one parent with the disease, the risk of that person becoming schizophrenic is 8%-10%, ten times greater than the general population. There is no gene that causes schizophrenia. There are several promising brain-expressed genes (dysbindin 1, neuregulin 1 to name two) whose products interact with glutamate receptors that may be associated with schizophrenia, but further studies in other populations are necessary to replicate any associated findings.
Bipolar affective disorder is also known as manic-depressive disorder. It is characterized by excessive mood swings, either to extremely happy (manic) or extremely sad (depressive). This is influenced mainly by genetics. The incidence of the disease rises to 5% to 10% over the general population for people with first-degree relatives who have the disease.
How can chromosomal banding be used?
By using banding techniques chromosomes can be unambiguously numbered and individual variation in chromosome composition can be studied.
How do cells communicate, and what is the significance of this communication?
Cells communicate in three ways 1) they display plasma membrane bound signaling molecules (receptors) that affect the cell itself and other molecules that are in direct physical contact. 2) they affect receptor proteins inside the target cell and the signal molecule has to enter the cell to bind to them 3) they form protein channels (gap junctions) that directly coordinate the activities of adjacent cells. Cells need to communicate to maintain homeostasis, to regulate their growth and division and their development and organization into tissues; and to coordinate their functions.
What is the difference between mitosis and meiosis?
Chromosome behavior Mitosis: Homologous chromosomes independent Meiosis: Homologous chromosomes pair forming bivalents until anaphase I Chromosome number- reduction in meiosis Mitosis- identical daughter cells Meiosis- daughter cells haploid Genetic identity of progeny: Mitosis: identical daughter cells Meiosis: daughter cells have new assortment of parental chromosomes Meiosis: chromatids not identical, crossing over Meiosis, as described above, is the process by which certain sex cells are created. If you're male, your body uses meiosis to create sperm cells; if you're female, it uses meiosis to create egg cells. Others cells in your body contain 46 chromosomes: 23 from your father and 23 from your mother. Your egg (or sperm) cells contain only half that number—a total of 23 chromosomes. When an egg and sperm unite to make a fertilized egg, the chromosomes add up to equal 46.
Of what are chromosomes composed?
Chromosomes are long strands of DNA coiled in the nucleus of cells that contain the genetic code for an individual. Each person receives half of his or her chromosomes from each parent.
What are some current examples of multifactorial disorders that are so prevalent in our adult society today?
Coronary heart disease is the cause of 25% of the deaths in the United States today. The two causative factors include atherosclerosis (narrowing of the coronary arteries due to cholesterol plaque formation) and myocardial infarction (when the heart is deprived of oxygen due to the atherosclerosis and the heart tissue dies). When this process occurs in the brain, a stroke occurs. Risk factors for coronary heart disease include: A positive first-degree relative High blood pressure (hypertension) High fat intake (high cholesterol) Obesity Smoking This risk increases with: More affected family members Affected family members are female (less affected sex) Early age at onset in affected family members Familial hypercholesterolemia has been found to be an autosomal dominant gene disease process. This condition can be very severe, with cholesterol levels being twice as high as someone without the disease. Mortality rates are very high; cause of death is usually myocardial infarction before the age of 30. Primary hypertension is one of the leading causes of heart disease, renal disease (kidney failure), and stroke. Many factors coexist in the development of hypertension. Only 20% to 40% are hereditary factors. The rest, therefore, are environmental. These environmental factors include factors such as increased sodium intake, decreased physical activity, diabetes, and obesity (which are also affected by both genes and environment). There is no one specific gene for hypertension, although many genes contribute to primary hypertension, including genes that affect the sympathetic nervous system, renin-angiotensin- aldosterone system, and renal sodium transport.
What is crossover? What is recombination?
Crossover occurs during the first meiotic stage, the arms of homologous chromosome pairs intertwine and sometimes exchange portions of their DNA. Recombination: when crossing over occurs of all four pairs of alleles, this process of forming new arrangement is called recombination.
What is DNA polymerase?
DNA polymerase travels along the single DNA strand adding the correct nucleotides to the free end of the new strand and also performs a proofreading procedure to make sure the correct base is paired with the template base.
How does replication occur?
DNA replication consists of the breaking of weak hydrogen bonds between the bases, leaving a single strand with an unpaired base and then complementary base pairing occurs and a new double stranded identical molecule is formed.
What is an example of a chromosomal deletion, and how does it manifest itself clinically?
Deletions—Cri du chat syndrome is the consequence of deletion of part of the short arm of chromosome 5, resulting in a characteristic cry, low birth weight, mental retardation, microcephaly, and heart defects.
After heart disease, cancer is the next leading cause of death in the United States. There is a known genetic link when it comes to cancer and families. There are also many environmental factors such as smoking that lead to the development of cancer in people. Breast Cancer There is a strong family history link when it comes to breast cancer in women. This risk increases if: There is an affected first-degree relative The affected relative is young Tumors are found in both breasts
Diabetes mellitus (DM) is a complex disorder; its cause is not yet fully understood. DM type 1 usually manifests itself before the age of 40. The T cells of one's own body destroy the insulin-making ability of the beta cells found in the pancreas. All indications are that this is an autoimmune disease. Siblings of a person with type 1 DM are at greater risk of developing the disease (about 6%) as opposed to the general population (whose risk is 0.3%-0.5%). Studies with identical twins show that the risk of developing type 1 DM jumps to about 50%. Type 2 DM is more common than type 1, accounting for 90% of all DM cases. With type 2 DM, there is some insulin being made by the pancreas. People who have type 2 DM have cells that are resistant to the uptake of insulin. This is especially common among people who are obese. There is a disturbing trend recently among people younger than age 25, who are obese and develop type 2 DM. This is most likely, in part because of an autosomal dominant inheritance. People with this type of DM are considered to have maturity-onset diabetes of the young (MODY). Half of these cases are caused by mutations in the glucokinase gene (plus other genes).
What is meant by dominant and recessive allele?
Dominant allele: effects are observable in the heterozygote Recessive allele: effects are observable only in the homozygote
How might a duplication differ from a deletion?
Duplications—This condition is usually not as harmful as deletions, but duplication of the short arm of chromosome 5 causes mental retardation with less serious physical defects.
How does DNA code for gene products?
Each DNA subunit consists of one deoxyribose molecule, one phosphate group, and one base (called nucleotide). Triplets of bases (Codons) make 64 amino acids. Proteins are composed of one or more polypeptides (sequences of amino acids)
What does codominant mean?
Effects of both alleles are observable in the heterozygote. Example A and B blood type is displayed as AB blood type.
What are the components of cells, and what are their functions?
Endoplasmic reticulum- synthesizes and metabolizes lipids Lysosome- contains degradative enzymes Cytoskeleton- maintains cell shape Ribosome- synthesizes proteins Golgi apparatus- processes and packages proteins and lipids Mitochondria- makes ATP Nucleus- contains genetic material
What is expressivity, and how does it affect phenotype?
Even if penetrance for an autosomal dominant genetic disorder is complete, there is still variation among the severity of symptoms in affected individuals. This is called variable expressivity and may result from the presence of modifier genes and environmental factors.
What are the recurrence risks and patterns of transmission for diseases?
For single gene diseases 50% for typical autosomal dominant disease and 25% for autosomal recessive diseases.
What is the fragile X syndrome?
Fragile Sites—Fragile sites are areas prone to developing breaks and gaps, although the sites are not usually related to disease. However, one site is known as the fragile X site. Inheriting this gene leads to mental retardation.
How is gender determined?
Gender is determined by the presence of the Y chromosome. This occurs beginning in the 6th week of gestation.
Are the genders affected equally or disproportionately by this mode of inheritance?
Genders are equally affected in autosomal recessive inheritance.
What is meant by gene splicing?
Gene splicing is a post-transcriptional modification in which a single gene can code for multiple proteins. Gene Splicing is done in eukaryotes, prior to mRNA translation, by the differential inclusion or exclusion of regions of pre-mRNA. Gene splicing is an important source of protein diversity.
What are genes?
Genes are the basic units of inheritance
What is the relationship between genotype and phenotype?
Genotype is the composition of genes at a given locus. The phenotype is the outward appearance that is influenced by genes and environment.
How do growth factors stimulate cell proliferation?
Growth factors also called cytokines are peptides that transport signals within and between cells. Cells need nutrients and growth factors for proliferation. These signals act to overcome intracellular braking mechanisms that tend to restrain cell growth and block progress through the cell cycle.
What is meant by homozygous and heterozygous?
Homozygous: Both alleles at a given locus are identical. Heterozygous: Alleles at a given locus are different from one another. One member of the chromosome pair contributed by the father and one by the mother. At a given locus an individual has one gene whose origin is paternal and one whose is maternal. When the two genes are identical, the individual is homozygous at that locus.
Read Chapter 4, pages 142-143 in your textbook.
How are gametes and somatic cells different? Gametes include sperm and egg cells with only 23 chromosomes and somatic cells include all other cells other than gametes and have 46 chromosomes.
Is it possible for an affected child to be born to two normal parents?
If a child is born with an autosomal dominant disease and there is no family history of that disease, then one of the parent's germ cells must have acquired a new mutation.
What is an inversion, and what is the position effect?
Inversions—Affected individuals usually have no physical effect, but inversions may affect the genes transmitted to the offspring of the carrier.
What is meant by consanguinity, and how does it increase the risk of having affected offspring?
Marriage between related individuals, on average one fourth of the offspring of carrier parents will be affected.
What is the process of mitosis and cytokinesis?
Mitosis describes the process by which the nucleus of a cell divides to create two new nuclei, each containing an identical copy of DNA. (Cytokinesis describes the division of the rest of the cell.)
What is a mutagen?
Mutagens are agents that cause mutations in the DNA and include many environmental exposures such as radiation and industrial chemicals. Cigarette smoke is one of the most important sources of mutagens throughout the world.
What is a mutation? What are some examples?
Mutation is a change in the DNA template that can result in abnormal DNA, RNA, and protein synthesis. Some mutations occur by chance (in the absence of mutagens) and are called spontaneous mutations. These occur more frequently in vulnerable parts of the human DNA (mutational hot spots) and are associated with many human diseases. Some DNA mutations are subtle or "silent" and cause no problems. Others are repaired by the cell before they can cause disease. More serious mutations lead to cell death, cell dysfunction, or transformation into cancerous cells. Missense mutation: A genetic change that results in the substitution of one amino acid in protein for another. A missense mutation is responsible for sickle hemoglobin, the molecular basis of sickle cell trait and sickle cell anemia. Nonsense mutation: A mutation (a change) in a base in the DNA that prematurely stops the translation (reading) of messenger RNA (mRNA) resulting in a polypeptide chain that ends prematurely and a protein product that is truncated (abbreviated) and incomplete and usually nonfunctional. Frameshift mutations: Base pair deletions or additions cause what are called frameshift mutations. These mutations occur when the sequencing of base pairs is altered, resulting in abnormal DNA replication and RNA and protein synthesis.
What is nondisjunction?
Nondisjunction during gametogenesis is the most common cause of aneuploidy. Nondisjunction means that the chromosomes do not separate equally during meiosis so that one gamete gets both copies of a chromosome, and the other gamete gets none.
Why don't women have twice as much effect from the X-linked genes as men do?
Only few X linked dominant traits exist therefore in an X linked recessive trait the normal allele counteracts the disease causing allele.
What are the ways in which molecules can pass in and out of the cell?
Passive transport: Diffusion, Filtration, and osmosis Mediated and Active transport: passive mediated transport by protein transporter no energy used, active transport requires energy and protein transporter moves molecules against the concentration gradient. Transport by vesicle formation: endocytosis, exocytosis
What is an example of a Robertsonian translocation?
Robertsonian translocation occurs in chromosomes 13, 14, 15, 21, and 22 and while the affected individual appears normal, they have 45 chromosomes instead of 46. The offspring of affected individuals may have serious genetic abnormalities, such as Down syndrome.
What are RNA and some of its components?
RNA is single strand structure pairing adenine with uracil and guanine with cytosine. RNA mediates transcription and translation.
What is Turner syndrome, and how does it manifest itself clinically?
Single X chromosome only affects females, usually causes sterility. Displays as short stature, webbing of neck, widely spaced nipples, coarctation of the aorta, sparse body fair, and edema of the feet in newborns.
What is meant by penetrance, and how does that affect whether an individual is affected by a genetic defect?
Some individual who inherit an autosomal dominant gene do not develop the full expression of the disease and are only mildly affected. This results from incomplete penetrance of a trait.
What are congenital diseases? How are they different from multifactorial disorders?
Some multifactorial diseases that are common at birth are called congenital malformations. Somewhere around 2% of all babies are born with a congenital malformation. Below is a list of the most common congenital malformations in white newborns. Disorder Prevalence per 1000 Births (Approximate) Cleft lip/palate 1 Clubfoot 1 Congenital heart defects 4-8 Hydrocephaly 0.5-2.5 Isolated cleft palate 0.4 Neural tube defects 1-3 Pyloric stenosis 3
Is it possible for an affected child to be born to two normal parents?
Testing for the carrier state is available for some of the most common recessive diseases and can be used for genetic counseling of prospective parents. On average, 25% of offspring will be affected with the disease when both parents are carriers.
What is complementary base pairing?
The consistent pairing of adenine with thymine and of guanine with cytosine which is needed for accurate DNA replication.
Are the genders affected equally or disproportionately by this mode of inheritance?
The genders are affected equally in in autosomal dominant inheritance.
Epigenetics describes changes in gene function that are not the result of changes in the DNA sequence.
The most important epigenetic factor is gene methylation (also called gene silencing). Attachment of methyl groups to DNA alters gene activity and is implicated in several diseases. The clinical application of an understanding of methylation has been explored in cancer diagnosis, prognosis, and treatment.
What are the potential benefits of a map of the human genome?
The rate of crossing over can be used to infer the distance between two loci on a chromosome because the probability of crossovers occurring between two loci increases as the loci become more distant.
What are the sex chromosomes?
The remaining chromosome pair consists of two homologous X chromosomes in females or a non homologous pair X and Y in males.
What is metaphase?
The second stage of cell division, between prophase and anaphase, during which the chromosomes become attached to the spindle fibers.
How do you analyze the risk that a person will develop a certain disease?
There are several standards by which multifactorial inheritance is judged: 1) The more people in a family that are affected by the disease, the greater the risk. 2) If the disease is expressed in its most severe form by the person who first contracted it (proband), then the risk to subsequent generations is increased. 3) The risk is higher than the stated relative risk if the disease occurs in the more uncommon (of the two) genders; that is if the less common gender contracts the disease, the relative risk is higher. 4) The further displaced a relative is from the proband, the relative risk decreases by half (offspring, 50%; niece-aunt, 25%; first cousins, 12.5%' and so on). 5) A virgule (/) indicates the prevalence of a disease in a certain population.
Obesity is defined as having a body mass index (BMI) greater than 30. Many people in our society today are either obese or overweight. While obesity in and of itself is not a disease per se, it is a significant risk factor for other diseases, such as heart disease, kidney disease, stroke, high blood pressure, and type II DM. There are a few known genes, including the leptin gene, that have an effect on weight in people. There are only a few known cases of this gene causing obesity. The greatest DNA variant that is known to cause the increased risk of obesity is the FTO gene.
This disease, written about in a 1906 paper by the doctor whose name it bears, accounts for about 70% of the total cases of mental disability in the adult population. Alzheimer Disease is characterized by the formation of amyloid plaques and neurofibrillary tangles in the cerebral cortex and hippocampus of the brain. In turn, these cause such symptoms in the individual with the disease as progressive dementia and memory loss. Death will occur in these people within 7 to 10 years after the first signs and symptoms appear. The risks of developing Alzheimer Disease increase with a first-degree relative with the disorder. Genes or mutations of genes associated with the disease are: Presenilin 1 and presenilin 2 (early onset) Amyloid-8 precursor protein that encodes itself (on chromosome 21) (Down syndrome) Allelic variation in the apolipoprotein E locus (responsible for clearing amyloid from the brain)
What is the basic model of multifactorial inheritance? What is the threshold model?
Threshold Model explains why one sex might be more likely than the other to contract a certain disease.The threshold of liability must be crossed for the disease to be expressed in an individual. The diseases that do not follow the bell curve have an underlying liability distribution.
What is transcription, and how does it work?
Transcription is the process by which RNA is formed from DNA to carry the genetic code into the cytoplasm where proteins are synthesized. Messenger RNA (mRNA) is formed from DNA that has been "unzipped" (like in DNA replication), but instead of DNA polymerase, it is RNA polymerase that binds to a promoter site, pulls the DNA strands apart, and starts matching the base pairs. Complementary base pairing occurs and is similar to that in DNA replication, but remember that RNA uses uracil to match with adenine (instead of thymine).
How do transcription and translation occur?
Transcription is the process by which RNA is synthesized from a DNA template the result is mRNA( messenger RNA). Transcription of a gene occurs by RNA polymerase and transcription factors which can activate or repress expression of genes. Translation is the process by which RNA directs the synthesis of a polypeptide. mRNA interacts with tRNA (Transfer RNA) by complementary base pairing and an amino acid binds to the tRNA thus beginning a polypeptide chain until a ribosome binds to a termination signal and stops translation and polypeptide formation.
What is translation, and how does it work?
Translation is the process by which mRNA interacts with transfer RNA (tRNA) in the ribosome and results in the formation of amino acid sequences that bind together to form polypeptides and eventually proteins. The mRNA that has been transcribed in the nucleus moves into the cytoplasm and binds with a ribosome at a particular sequence of mRNA base pairs called an initiation site (the codon AUG for methionine). The ribosome moves along the mRNA and matches each codon with an anticodon on tRNA. As each tRNA is added to the mRNA strand, it brings with it an amino acid that is specific to the codons on the mRNA. The amino acids bind to one another sequentially, forming polypeptide chains. Termination of translation occurs when the ribosome encounters one of three termination codons on the mRNA (UAA, UAG, or UGA).
What are the two major kinds of translocations, and how do they differ?
Translocations—There are two types: reciprocal translocation and Robertsonian translocation. Reciprocal translocation usually does not result in phenotype abnormalities, but abnormal genes passed to offspring may create physical abnormalities.
What is the usual outcome of triploidy or tetraploidy in a zygote?
Triploidy and tetraploidy account for about 10% of miscarriages and are incompatible with survival of the fetus.
What is Klinefelter syndrome, and how does it manifest itself clinically?
Two XX chromosomes and Y chromosome makes those have a male appearance and become males. Displays usually with gynecomastia, testes are small, body hair is sparse, stature is elevated, voice is somewhat high pitched, and moderate mental impairment may be present. Risk increases with maternal age and nondisjunction.
Why are some mutations more common in humans than others?
We are exposed to several mutagens
Read Chapter 4, pages 135-142 in your textbook.
What are chromosomes? Microscopic threadlike structures within the nucleus that contain genes.
Read Chapter 4, pages 148-151 in your textbook.
What are clastogens? Chromosomes can break, especially in the presence of harmful substances called clastogens (toxins, radiation, infections).
Read Chapter 4, pages 142-143 in your textbook.
What are polyploid cells? Polyploidy occurs when abnormal gametogenesis leads to the embryo having three (triploidy) or even four (tetraploidy) times the normal number of chromosomes
Read Chapter 5 in your textbook.
What are the concepts of incidence and prevalence? How do they relate to diseases? Incidence: The number of new cases of a disease reported divided by the number of people in that population over a 1-year period. Prevalence: The numbers of people in a given population that have a certain disease at a given point in time. The incidence rate for a certain disease plus the rate of people surviving that same disease comprises the prevalence rate.
Read Chapter 1 in your textbook.
What are the functions of cells? The 8 functions are as follows: 1) Movement 2) Conductivity 3) Metabolic Absorption 4) Secretion 5) Excretion 6) Respiration 7) Reproduction 8) Communication
Read Chapter 4, pages 159-160 in your textbook.
What does linkage mean when used to refer to gene loci? Some genes that occupy the same region of a chromosome do tend to be transmitted together to the offspring.
Read Chapter 4, pages 156-159 in your textbook, and carefully review the Punnett square in Figure 4-27 on page 158.
What does sex-linked mean? Why are males called hemizygous for some genes? Sex linked means that some conditions come from the sex chromosomes. Males are called hemizygous for some genes because a male who inherits a recessive disease gene on the X chromosome will be affected by the disease because the Y chromosome does not carry a normal allele to counteract the disease causing allele.
Read Chapter 4, pages 141-142 in your textbook.
What is RNA, and what are its components? Ribonucleic acid (RNA) reads the genetic code on the DNA and directs protein synthesis
Read Chapter 4, page 151 in your textbook.
What is a locus and what is an allele? What is meant by polymorphism? Locus: the position for a specific gene on a each paired chromosome. Allele: The gene at a particular locus polymorphism: a locus containing two or more alleles that each occur with an appreciable frequency in a population is said to be polymorphism.
Read Chapter 4, pages 135-142 in your textbook.
What is complementary base pairing? Complementary base pairing means that the appropriate new nitrogenous base is linked by DNA polymerase to each of the bases in the template from the unzipped DNA strand. This results in the formation of a new double strand of DNA that is identical to the original
Read Chapter 4, pages 151-154 in your textbook, and carefully review the Punnett square in Figure 4-20 on page 153 and the pedigree in Figure 4-21 on page 153.
What is the usual pattern of mating that gives rise to offspring affected by an autosomal dominant trait? Autosomal dominant inheritance means that the phenotypic trait is expressed whenever the gene is present, whether in the homozygote or the heterozygote. Autosomal dominant gene mutations are rarely homozygous, so the vast majority of mating occurs between a heterozygous affected parent and a normal parent (both alleles normal). As you can see, 50% of the offspring from this mating will be affected.
Read Chapter 4, pages 153-156 in your textbook, and carefully review Figures 4-24 and 4-25 on page 155.
What is the usual pattern of mating that gives rise to offspring affected by an autosomal recessive trait? Autosomal recessive inheritance that results in disease is uncommon in the general population, but it is more common among members of close-knit populations. This increased incidence results because in these populations, there is an increased likelihood that the parents will be related, thus making it more likely that two carriers will mate. Autosomal recessive inheritance means that the trait is expressed only when the individual is homozygous for the abnormal gene. Thus parents may be unaffected carriers yet transmit the trait or the disease to their offspring. The likelihood that two carriers will mate is increased by consanguinity (having a blood relationship).
What is genomic imprinting?
When the effect of a mutation is dependent upon from which parent trait was inherited>>Only involves a few traits. Example Prader Willi syndrome or Angelman syndrome.
What is meant by trisomy 21? What are the risk factors for this condition? How does it manifest itself in an individual?
When these gametes join with a normal gamete during fertilization (which contains one copy of each chromosome), the resulting embryo will have either one too many (trisomy) or one too few (monosomy) chromosomes. 3 chromosomes on chromosome pair 21, Down's syndrome occurs in 1 in 800 births risk increases with maternal age. Displays as a low nasal bridge, epicanthal folds, protruding tongue, and flat low set ears, poor muscle tone, and short stature. Trisomy 21 also increases risk of congenital heart defects, reduced ability to fight respiratory tract infections, increased susceptibility to leukemia and Alzheimer's disease.
What is Duchenne muscular dystrophy, and how does it manifest itself clinically?
X linked recessive inheritance, seen much more in males than females. Progressive muscle weakness, unable to walk by age 12.
Why are X-linked recessive diseases more common in males?
X-linked recessive inheritance means that the trait is expressed in any male that carries it, but it is only expressed in a female if she is homozygous for the abnormal gene. This is because males have a Y gene instead of an additional normal X gene to "hide" the recessive gene. Thus the mother may be an unaffected carrier and the father may be normal, yet they may transmit the trait or the disease to their sons. Because an affected male and a carrier mother would have to mate to transmit the disease to a daughter, this is quite rare. On average, 50% of sons will be affected with the disease when the mother is a carrier.
What is the basic structure of DNA?
genes are made up of sequences of DNA, DNA is made up of nitrogenous bases bound by a weak hydrogen bond.
How does the cell get its energy?
phase 1: digestion breakdown of proteins, polysaccharides, and fats by enzymes phase 2: glycolysis and oxidation occurs in cytoplasm of cell if oxygen present it forms 2 ATP and 2 pyruvate molecules which can then enter the mitochondria and begin the citric acid cycle. If oxygen is not present pyruvate acid transforms to lactic acid. phase 3: citric acid cycle (krebs cycle) ends with oxidative phosphorylation occurs in the mitochondria