162 Questions
Why are humans not convenient subjects for genetic research?
Because humans have a long generation span
What enables the study of human genetics despite the limitations?
New molecular biological techniques
What is the purpose of pedigree analysis in human genetics?
To analyze the results of matings that have already occurred
What is the genotype of the two grandparents with widow's peaks in the pedigree?
Ww
What is the genotype of the offspring in the second generation who do not have widow's peaks?
ww
What can be inferred about the genotype of the sister in the third generation who has a widow's peak?
She is either homozygous dominant (WW) or heterozygous (Ww)
What is the purpose of constructing a family pedigree?
To analyze the results of matings that have already occurred
Why is the widow's-peak allele considered dominant?
Because it is always expressed in the phenotype
What is the probability that the child will have a widow's peak?
3/4
What is the probability that the child will be unable to taste PTC?
1/4
What is the chance that the child will have a widow's peak and be unable to taste PTC?
3/16
What type of disorders are thousands of genetic disorders known to be inherited as?
simple recessive traits
What is the function of genes that code for proteins?
To synthesize proteins of specific function
What is an example of a relatively mild recessively inherited disorder?
Albinism
What is an example of a life-threatening recessively inherited disorder?
Cystic fibrosis
What is the purpose of pedigree analysis in the context of genetic disorders?
To predict the risk of an individual inheriting a disorder
What is the frequency of cystic fibrosis among people of European descent?
One out of 2,500
What is the effect of the abnormal allele in cystic fibrosis?
Abnormal transport of chloride ions
What is the main difference between sickle-cell disease and cystic fibrosis?
The population affected by the disease
What is the effect of having a single copy of the sickle-cell allele?
Reduced frequency and severity of malaria attacks
What is the frequency of sickle-cell trait among African-Americans?
One out of 10
What is the reason why the sickle-cell allele has not disappeared from the population?
It provides protection against malaria
What is the effect of low oxygen content in the blood of individuals with sickle-cell disease?
The hemoglobin proteins aggregate into long fibers
What is the treatment for sickle-cell disease?
All of the above
What is the relationship between the normal and sickle-cell alleles at the molecular level?
The two alleles are codominant
What is the effect of the abnormal allele in sickle-cell disease?
The production of abnormal hemoglobin proteins
What is the advantage of having sickle-cell hemoglobin in tropical Africa?
It provides protection against malaria.
Why are lethal dominant alleles less common than recessive alleles with lethal effects?
Because they are often not passed on to future generations.
What is the characteristic of Huntington's disease?
It is a degenerative disease of the nervous system.
What is the probability of a child inheriting the Huntington's disease allele from a parent with the allele?
50%
What is the result of having a dominant allele for achondroplasia?
The individual has the dwarf phenotype.
Why may some individuals not want to be tested for Huntington's disease?
Because they may not want to know the result.
What is the purpose of constructing a genetic test for Huntington's disease?
To determine the genotype of individuals with a family history of the disease.
What is the significance of the discovery of the Huntington's allele?
It enabled the development of a genetic test for the disease.
Why is achondroplasia considered a dominant trait?
Because it is expressed in heterozygous individuals.
What is the frequency of achondroplasia in the population?
1 in 25,000 people.
What type of allele is responsible for causing a genetic disorder?
Recessive
What is the genotype of a carrier of a recessive disorder?
Aa
What is the probability of a child inheriting a double dose of the recessive allele in a mating between two carriers?
1/4
Why are recessive homozygotes less common in a population?
They die before reproductive age
What is the reason for the uneven distribution of genetic disorders among populations?
Different genetic histories of the world's peoples
What is the effect of consanguineous matings on the probability of passing on recessive traits?
It increases the probability
Why do many societies and cultures have laws or taboos against marriages between close relatives?
To reduce the incidence of inherited diseases
What is the consequence of inbreeding in domesticated and zoo animals?
An increase in autosomal recessive conditions
What is the predicted genotypic ratio for the offspring of two carriers of a recessive allele?
1 AA : 2 Aa : 1 aa
Why do heterozygotes typically have a normal phenotype in recessive disorders?
Because the dominant allele produces a sufficient amount of the specific protein
What is the main difference between simple Mendelian disorders and multifactorial disorders?
Simple Mendelian disorders are caused by a single genetic locus, whereas multifactorial disorders have a genetic component plus an environmental influence.
What is the benefit of genetic testing and counseling?
It can help avoid simple Mendelian disorders by assessing the risk of a particular genetic disorder before conception or during pregnancy.
What is the probability that John and Carol's firstborn will have the disease if they are both carriers?
1/9
What is the probability that John and Carol's subsequent children will have the disease if their first child has the disease?
1/4
What is the effect of lifestyle on multifactorial characters?
It reduces the risk of the disease.
What is the ratio of genotypes of offspring of an Aa x Aa cross?
1 AA:2 Aa:1 aa
What is the probability of John and Carol both being carriers of the recessive allele?
2/3
What is the probability that John and Carol's first three children will all have the disease?
1/64
What is the relationship between the genotype of a child and the genotypes of older siblings?
The genotype of a child is independent of the genotypes of older siblings.
What is the role of genetic counselors in hospitals?
They provide information to prospective parents concerned about a family history for a specific disease.
What is the primary purpose of cell-free fetal DNA tests and other blood tests in prenatal screening?
To identify potential genetic disorders and recommend further testing
What is the main advantage of ultrasound and isolation of fetal cells or DNA from maternal blood compared to other procedures?
They are less invasive and pose no known risk to the mother or fetus
Why are amniocentesis or CVS generally offered to women over age 35?
Because they are at a higher risk of having a child with Down syndrome
What is the result of parental and fetal screening for Tay-Sachs alleles done since 1980?
A reduction in the number of children born with Tay-Sachs by 90%
What is the purpose of newborn screening for phenylketonuria (PKU)?
To detect PKU and allow for normal development through a special diet
What is the consequence of not detecting PKU in a newborn?
Severe intellectual disability
Why is the artificial sweetener aspartame excluded from the diet of individuals with PKU?
Because it contains phenylalanine
What is the basis of fetal and newborn screening for serious inherited diseases?
The Mendelian model of inheritance
What is the significance of Gregor Mendel's discoveries in the field of genetics?
He established the concept of heritable factors transmitted according to simple rules of chance
What is the outcome of the Chinese government's program of fetal testing to detect β-thalassemia?
A reduction in the rate of β-thalassemia from over 21 births per 1000 to just under 13 in 2011
What is the probability that a fourth child of a couple will have a recessive disease if the previous three children have the disease?
1/4
What is the purpose of tests for identifying carriers of recessive alleles?
To determine the genetic risk for a particular disease
What is the significance of the Genetic Information Nondiscrimination Act of 2008?
It prohibits discrimination in employment based on genetic test results
What is the purpose of amniocentesis?
To detect certain chromosomal defects
What is the advantage of chorionic villus sampling (CVS) over amniocentesis?
CVS can be performed earlier in pregnancy
What is the significance of the discovery of fetal cells or DNA in the mother's blood?
It allows for prenatal genetic testing
What is the significance of karyotyping?
It identifies genetic disorders caused by chromosomal defects
What is the importance of genetic counseling in the context of genetic disorders?
It helps individuals make informed decisions about having children
What is the significance of advances in biotechnology?
They have the potential to reduce human suffering
What is the purpose of testing for carriers of recessive alleles?
To determine the genetic risk for a particular disease
What is the probability of a child inheriting a dominant allele and having a widow's peak in a monohybrid cross?
3/4
What is the probability of a child being homozygous recessive for the ability to taste PTC in a monohybrid cross?
1/4
What is the assumption made in the dihybrid cross of widow's peak and ability to taste PTC?
The genes are on different chromosomes
What is the purpose of pedigree analysis in human genetics?
To study the genetic disorders in a family
What is the characteristic of recessively inherited disorders?
They are inherited as simple recessive traits
What is the function of genes that code for proteins?
To code for specific proteins
What is the effect of the abnormal allele in recessively inherited disorders?
It leads to the production of a faulty protein
What is the advantage of pedigree analysis in the context of genetic disorders?
It helps to predict the probability of a child inheriting a disorder
What is the frequency of cystic fibrosis among people of European descent?
One out of 2,500
What is the result of the abnormal allele in cystic fibrosis?
An abnormally high concentration of intracellular chloride
What is the frequency of sickle-cell trait among African-Americans?
One out of 10
What is the effect of having a single copy of the sickle-cell allele?
Reduced severity of malaria attacks
What is the relationship between the normal and sickle-cell alleles at the molecular level?
The two alleles are codominant
What is the main difference between sickle-cell disease and cystic fibrosis?
One is caused by a single amino acid substitution, the other is caused by a membrane protein defect
What is the treatment for sickle-cell disease?
Regular blood transfusions
Why has the sickle-cell allele not disappeared from the population?
Because it has a selective advantage in areas where malaria is common
What is the effect of low oxygen content in the blood of individuals with sickle-cell disease?
The sickle-cell hemoglobin proteins aggregate into long fibers
What is the advantage of having sickle-cell hemoglobin in tropical Africa?
It provides protection against malaria
What is the result of inheriting a double dose of a recessive allele in a recessive disorder?
A more severe phenotype
Why are heterozygotes typically carriers of a recessive disorder?
Because they can transmit the recessive allele to their offspring
What is the predicted genotypic ratio for the offspring of two carriers of a recessive allele?
1 AA:2 Aa:1 aa
Why are recessive homozygotes less common in a population?
Because they are less likely to survive and reproduce
What is the reason for the uneven distribution of genetic disorders among populations?
Different genetic histories of the world's peoples
What is the effect of consanguineous matings on the probability of passing on recessive traits?
It increases the probability
What is the consequence of inbreeding in domesticated and zoo animals?
It increases the probability of genetic disorders
Why do many societies and cultures have laws or taboos against marriages between close relatives?
To prevent genetic disorders
What is the probability that a child will inherit a double dose of the recessive allele in a mating between two carriers?
1/4
What is the genotypic ratio of offspring with a normal phenotype in a mating between two carriers of a recessive allele?
2:3
What is the main characteristic of multifactorial disorders?
Have a genetic component plus a significant environmental influence
What is the role of genetic counselors?
To provide information to prospective parents concerned about a family history for a specific disease
What is the probability that John and Carol's firstborn will have the disease if they are both carriers?
1/9
What is the result of each child representing an independent event in the sense that its genotype is unaffected by the genotypes of older siblings?
The genotype of each child is independent of the genotypes of older siblings
What is the difference between simple Mendelian disorders and multifactorial disorders?
Simple Mendelian disorders are caused by a single gene, while multifactorial disorders are caused by multiple genes and environmental factors
What is the purpose of genetic testing and counseling?
To provide information to prospective parents concerned about a family history for a specific disease
What is the probability that John and Carol's subsequent children will have the disease if their first child has the disease?
1/4
What is the benefit of genetic testing and counseling?
It can provide information to prospective parents concerned about a family history for a specific disease
What is the probability that a child will have the disease if both parents are carriers?
1/4
What is the result of a mating between two carriers of a recessive allele?
A 1/4 chance of having a child with the disease
What is the advantage of having sickle-cell hemoglobin in tropical Africa?
Reduced risk of malaria
What is the characteristic of a lethal dominant allele?
Causes death before reproductive age
What is the reason why lethal dominant alleles are less common than recessive alleles with lethal effects?
They are often lethal before reproductive age
What is the effect of a single copy of the sickle-cell allele?
It reduces the risk of malaria
What is the frequency of achondroplasia in the population?
One in every 25,000 people
What is the purpose of genetic testing for Huntington's disease?
To identify carriers of the allele
What is the result of having a dominant allele for achondroplasia?
A dwarf phenotype
Why may some individuals not want to be tested for Huntington's disease?
They are afraid of the test results
What is the probability of a child inheriting the Huntington's disease allele from a parent with the allele?
50%
What is the significance of the discovery of the Huntington's allele?
It allows for the development of a genetic test for the disease
What is the purpose of cell-free fetal DNA tests and other blood tests?
To diagnose genetic disorders in the fetus
What is the risk posed by ultrasound and isolation of fetal cells or DNA from maternal blood?
No known risk to the mother or fetus
What is the chance that a fourth child of a couple will have a recessive disease if the first three children have the disease?
1/4
What is the purpose of tests for identifying carriers of recessive alleles?
To find out whether the prospective parents are heterozygous carriers
Why are women over 35 offered amniocentesis or CVS for diagnostic testing?
Due to their increased risk of bearing a child with a genetic disorder
What is the result of parental and fetal screening for Tay-Sachs alleles?
A 90% reduction in the number of children born with Tay-Sachs disease
What is the benefit of the Genetic Information Nondiscrimination Act?
It prohibits discrimination in employment or insurance coverage based on genetic test results
What is the purpose of newborn screening programs?
To detect genetic disorders at birth
What is the purpose of amniocentesis?
To detect certain genetic disorders in the fetus
What is the advantage of chorionic villus sampling (CVS) over amniocentesis?
CVS can be performed earlier in pregnancy than amniocentesis
What is phenylketonuria (PKU)?
A recessively inherited disorder
What is the significance of the ability to analyze the entire genome of a fetus?
It allows for earlier detection of genetic disorders
What is the effect of a special diet low in phenylalanine on children with PKU?
It allows for normal development
What is the concern raised by the availability of genetic tests?
The tests may lead to discrimination in employment or insurance coverage
What is the basis of fetal and newborn screening for serious inherited diseases?
The Mendelian model of inheritance
What is the benefit of genetic counseling?
It provides prospective parents with informed decision-making about reproduction
Who is credited with the development of the 'gene idea'?
Gregor Mendel
What is the result of the Chinese government's program of fetal testing for β-thalassemia?
A reduction in the rate of β-thalassemia from over 21 births per 1000 to just under 13 in 2011
What is the purpose of isolating fetal cells or fetal DNA from the mother's blood?
To detect certain genetic disorders in the fetus
What is the benefit of advances in biotechnology?
They offer the potential to reduce human suffering
What is the key reason why the number of ATP molecules generated from the breakdown of one glucose molecule cannot be exactly stated?
Phosphorylation and redox reactions are not directly coupled.
What is the net ATP yield from the electrons passed to NAD+ in the mitochondrial matrix?
2.5 ATP
What is the role of electron shuttle systems in the mitochondrion?
To transport electrons from the cytosol into the mitochondrion
How many H+ ions are required to synthesize 1 ATP molecule?
4 H+ ions
What is the ATP yield from the electrons passed to FAD in the mitochondrial matrix?
1.5 ATP
Why do brain cells produce only about 1.5 ATP from each NADH that was originally generated in the cytosol?
Because electrons are passed to FAD in the mitochondrial matrix.
What is the effect of the slight energetic cost of moving ATP formed in the mitochondrion out into the cytosol?
It decreases the ATP yield.
What is the significance of the ATP yield varying slightly depending on the type of shuttle used to transport electrons from the cytosol into the mitochondrion?
It varies the ATP yield depending on the shuttle type.
What is the maximum number of ATP molecules produced by oxidative phosphorylation per glucose molecule, assuming all the proton-motive force generated by the electron transport chain is used to drive ATP synthesis?
32
What is the estimated efficiency of respiration in terms of the percentage of chemical energy in glucose transferred to ATP?
34%
What is the primary function of the uncoupling protein in the inner mitochondrial membrane of brown fat cells?
To generate heat without producing ATP
What is the effect of the adaptation in hibernating mammals, which allows them to generate heat without producing ATP?
It prevents the buildup of ATP, allowing cellular respiration to continue
What is the energy stored in one mole of ATP?
7.3 kcal
What is the energy released from the complete oxidation of one mole of glucose?
686 kcal
What is the approximate percentage of energy stored in gasoline that is converted to energy that moves a car?
25%
What is the role of the proton-motive force generated by the electron transport chain?
To drive ATP synthesis
What is the purpose of the uncoupling protein in hibernating mammals?
To generate heat without producing ATP
What is the benefit of the adaptation in hibernating mammals, which allows them to generate heat without producing ATP?
It allows them to survive during hibernation
Study Notes
Human Genetics
- Human traits often follow Mendelian patterns of inheritance, but studying human genetics is challenging due to the long human generation span and the ethical concerns of manipulating human breeding.
Pedigree Analysis
- Geneticists analyze the results of existing matings by collecting family history information and assembling it into a family tree, or pedigree, describing the traits of parents and children across generations.
- Pedigrees help understand the inheritance patterns of specific traits, such as the widow's peak hairline contour.
Widow's Peak Trait
- The widow's peak trait is caused by a dominant allele, W, and individuals lacking the trait must be homozygous recessive (ww).
- Individuals with the widow's peak can be either heterozygous (Ww) or homozygous dominant (WW).
PTC Tasting Ability
- The ability to taste PTC (phenylthiocarbamide) is a recessive trait, with the recessive allele represented by t and the dominant allele represented by T.
- Compounds similar to PTC are found in certain vegetables, such as broccoli and brussels sprouts, and account for their bitter taste.
Applications of Pedigree Analysis
- Pedigrees can help calculate the probability of a future child having a particular trait or genotype.
- Pedigree analysis is crucial in understanding the inheritance patterns of human traits and developing treatments for genetically based diseases.
Genotype and Phenotype
- A couple's child has a 3/4 chance of inheriting a dominant allele and a 1/4 chance of not inheriting it
- In a dihybrid cross, the probability of a child having a widow's peak and being unable to taste PTC is 3/16
Recessively Inherited Disorders
- Thousands of genetic disorders are inherited as simple recessive traits
- These disorders range in severity from mild to life-threatening
- Examples include albinism, cystic fibrosis, and sickle-cell disease
- Heterozygotes are typically phenotypically normal, but can be carriers of the disorder
- Recessive homozygotes (aa) may result from Aa * aa and aa * aa matings, but rarely reproduce
- Carriers may transmit the recessive allele to their offspring
Pedigrees and Consanguinity
- Close relatives are more likely to carry the same recessive alleles
- Consanguineous matings (e.g., siblings or first cousins) increase the probability of passing on recessive traits
- Laws and taboos against consanguineous marriages have evolved in many societies to prevent inherited diseases
Cystic Fibrosis
- A lethal genetic disease that affects 1 in 2,500 people of European descent
- Caused by a recessive allele that codes for a faulty membrane protein
- Symptoms include thick, sticky mucus in organs, poor nutrient absorption, and recurrent infections
- Treatment includes antibiotics, physical therapy, and dietary changes
- Gene therapy is being researched as a potential cure
Sickle-Cell Disease
- A genetic disorder that affects 1 in 400 people of African descent
- Caused by a recessive allele that alters hemoglobin production
- Symptoms include anemia, infections, and organ damage
- Heterozygotes have sickle-cell trait, which confers some resistance to malaria
- The allele is more common in African populations due to the selective pressure of malaria
Dominantly Inherited Disorders
- Some dominant alleles cause lethal diseases
- These alleles are relatively rare due to natural selection
- Examples include achondroplasia (dwarfism) and Huntington's disease
Multifactorial Disorders
- Many diseases have a multifactorial basis, involving both genetic and environmental factors
- Examples include heart disease, diabetes, and some mental illnesses
- Lifestyle choices can greatly impact the expression of these disorders
Genetic Testing and Counseling
- Genetic counseling can assess the risk of genetic disorders in offspring
- Tests can identify carriers of recessive alleles
- Fetal testing, such as amniocentesis, can detect genetic disorders in utero
- Ethical issues arise regarding genetic testing, including discrimination and informed decision-making### Prenatal Genetic Testing
- Genetic disorders can be detected through the presence of certain molecules in the amniotic fluid or by testing the DNA of cells cultured in the laboratory.
- Tay-Sachs disease can be detected through DNA testing of cultured cells from the amniotic fluid.
- A karyotype of these cultured cells can also identify certain chromosomal defects.
Chorionic Villus Sampling (CVS)
- CVS involves inserting a narrow tube through the cervix into the uterus to suction out a tiny sample of tissue from the placenta.
- The cells of the chorionic villi of the placenta have the same genotype and DNA sequence as the fetus.
- CVS can be performed as early as the 10th week of pregnancy and allows for rapid analysis, which is an advantage over amniocentesis.
Fetal Cells in Maternal Blood
- Fetal cells or DNA can be isolated from the mother's blood, allowing for genetic testing.
- In 2012, researchers were able to analyze the entire genome of a fetus using DNA from the mother's blood.
- Cell-free fetal DNA tests and other blood tests are increasingly being used as noninvasive prenatal screening tests.
Imaging Techniques
- Imaging techniques, such as ultrasound, allow for the examination of the fetus for major anatomical abnormalities.
- Ultrasound and isolation of fetal cells or DNA from maternal blood pose no known risk to either mother or fetus.
Prenatal Screening and Diagnosis
- Prenatal screening tests are offered to women over 35 due to their increased risk of bearing a child with Down syndrome.
- If the fetal tests reveal a serious disorder, the parents face the difficult choice of either terminating the pregnancy or preparing to care for a child with a genetic disorder.
- Parental and fetal screening for Tay-Sachs alleles has reduced the number of children born with this incurable disease by 90%.
Newborn Screening
- Genetic disorders can be detected at birth through simple biochemical tests.
- One common screening program is for phenylketonuria (PKU), a recessively inherited disorder that occurs in about one out of every 10,000–15,000 births in the United States.
- PKU can be detected through a simple biochemical test, and if treated with a special diet, can allow for normal development.
Genotype and Phenotype
- A couple's child has a 3/4 chance of inheriting a dominant allele and a 1/4 chance of not inheriting it
- In a dihybrid cross, the probability of a child having a widow's peak and being unable to taste PTC is 3/16
Recessively Inherited Disorders
- Thousands of genetic disorders are inherited as simple recessive traits
- These disorders range in severity from mild to life-threatening
- Examples include albinism, cystic fibrosis, and sickle-cell disease
- Heterozygotes are typically phenotypically normal, but can be carriers of the disorder
- Recessive homozygotes (aa) may result from Aa * aa and aa * aa matings, but rarely reproduce
- Carriers may transmit the recessive allele to their offspring
Pedigrees and Consanguinity
- Close relatives are more likely to carry the same recessive alleles
- Consanguineous matings (e.g., siblings or first cousins) increase the probability of passing on recessive traits
- Laws and taboos against consanguineous marriages have evolved in many societies to prevent inherited diseases
Cystic Fibrosis
- A lethal genetic disease that affects 1 in 2,500 people of European descent
- Caused by a recessive allele that codes for a faulty membrane protein
- Symptoms include thick, sticky mucus in organs, poor nutrient absorption, and recurrent infections
- Treatment includes antibiotics, physical therapy, and dietary changes
- Gene therapy is being researched as a potential cure
Sickle-Cell Disease
- A genetic disorder that affects 1 in 400 people of African descent
- Caused by a recessive allele that alters hemoglobin production
- Symptoms include anemia, infections, and organ damage
- Heterozygotes have sickle-cell trait, which confers some resistance to malaria
- The allele is more common in African populations due to the selective pressure of malaria
Dominantly Inherited Disorders
- Some dominant alleles cause lethal diseases
- These alleles are relatively rare due to natural selection
- Examples include achondroplasia (dwarfism) and Huntington's disease
Multifactorial Disorders
- Many diseases have a multifactorial basis, involving both genetic and environmental factors
- Examples include heart disease, diabetes, and some mental illnesses
- Lifestyle choices can greatly impact the expression of these disorders
Genetic Testing and Counseling
- Genetic counseling can assess the risk of genetic disorders in offspring
- Tests can identify carriers of recessive alleles
- Fetal testing, such as amniocentesis, can detect genetic disorders in utero
- Ethical issues arise regarding genetic testing, including discrimination and informed decision-making### Prenatal Genetic Testing
- Genetic disorders can be detected through the presence of certain molecules in the amniotic fluid or by testing the DNA of cells cultured in the laboratory.
- Tay-Sachs disease can be detected through DNA testing of cultured cells from the amniotic fluid.
- A karyotype of these cultured cells can also identify certain chromosomal defects.
Chorionic Villus Sampling (CVS)
- CVS involves inserting a narrow tube through the cervix into the uterus to suction out a tiny sample of tissue from the placenta.
- The cells of the chorionic villi of the placenta have the same genotype and DNA sequence as the fetus.
- CVS can be performed as early as the 10th week of pregnancy and allows for rapid analysis, which is an advantage over amniocentesis.
Fetal Cells in Maternal Blood
- Fetal cells or DNA can be isolated from the mother's blood, allowing for genetic testing.
- In 2012, researchers were able to analyze the entire genome of a fetus using DNA from the mother's blood.
- Cell-free fetal DNA tests and other blood tests are increasingly being used as noninvasive prenatal screening tests.
Imaging Techniques
- Imaging techniques, such as ultrasound, allow for the examination of the fetus for major anatomical abnormalities.
- Ultrasound and isolation of fetal cells or DNA from maternal blood pose no known risk to either mother or fetus.
Prenatal Screening and Diagnosis
- Prenatal screening tests are offered to women over 35 due to their increased risk of bearing a child with Down syndrome.
- If the fetal tests reveal a serious disorder, the parents face the difficult choice of either terminating the pregnancy or preparing to care for a child with a genetic disorder.
- Parental and fetal screening for Tay-Sachs alleles has reduced the number of children born with this incurable disease by 90%.
Newborn Screening
- Genetic disorders can be detected at birth through simple biochemical tests.
- One common screening program is for phenylketonuria (PKU), a recessively inherited disorder that occurs in about one out of every 10,000–15,000 births in the United States.
- PKU can be detected through a simple biochemical test, and if treated with a special diet, can allow for normal development.
Reasons for Inexact ATP Numbers
- Three reasons why the number of ATP molecules generated by the breakdown of one glucose molecule cannot be stated exactly:
- Phosphorylation and redox reactions are not directly coupled, resulting in a non-whole number ratio of NADH to ATP
- The exact number of H+ ions required to generate 1 ATP is debated, but most biochemists agree on 4 H+ ions
- ATP yield varies depending on the type of electron shuttle used to transport electrons from the cytosol into the mitochondrion
Electron Shuttles and ATP Yield
- The mitochondrial inner membrane is impermeable to NADH, so electrons are conveyed into the mitochondrion by electron shuttle systems
- Depending on the type of shuttle, electrons are passed either to NAD+ or FAD in the mitochondrial matrix
- The yield of ATP per NADH varies depending on the type of shuttle: 1.5 ATP (FAD) or 2.5 ATP (NAD+)
Proton-Motive Force and ATP Synthesis
- The proton-motive force generated by the electron transport chain is used to drive ATP synthesis and other kinds of work
- The proton-motive force can be used to drive the uptake of pyruvate from the cytosol or to generate heat instead of ATP
Efficiency of Respiration
- The efficiency of respiration is estimated to be around 34%, meaning that about 34% of the potential chemical energy in glucose is transferred to ATP
- The remainder of the energy is lost as heat, which is used to maintain body temperature and dissipated through sweating and other cooling mechanisms
This quiz covers the basics of human genetics, including the challenges of studying human traits and the use of pedigree analysis to understand inheritance patterns.
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