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Questions and Answers
A 50% loss of enzyme activity can be compensated for, involved genes do not encode ______ proteins.
A 50% loss of enzyme activity can be compensated for, involved genes do not encode ______ proteins.
enzyme
Two main types of nonenzyme proteins are ______.
Two main types of nonenzyme proteins are ______.
affected
The ______ activity of an enzyme can be compensated for without negatively impacting the overall function.
The ______ activity of an enzyme can be compensated for without negatively impacting the overall function.
loss
Involved genes do not encode ______ proteins.
Involved genes do not encode ______ proteins.
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There are ______ main types of nonenzyme proteins.
There are ______ main types of nonenzyme proteins.
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Those involved in regulation of ______
Those involved in regulation of ______
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Complex metabolic pathways are crucial for ______
Complex metabolic pathways are crucial for ______
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An example of a genetic disorder related to metabolism is ______
An example of a genetic disorder related to metabolism is ______
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______ pathways are interconnected and regulated in living organisms.
______ pathways are interconnected and regulated in living organisms.
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The regulation of metabolic pathways can affect ______ health.
The regulation of metabolic pathways can affect ______ health.
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A multifactorial trait is governed by the additive effect of 2 or more ______ of small effects.
A multifactorial trait is governed by the additive effect of 2 or more ______ of small effects.
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Multifactorial traits are also conditioned by ______ influences.
Multifactorial traits are also conditioned by ______ influences.
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Disorders with multifactorial inheritance can be defined as traits governed by the ______ effect of multiple genes.
Disorders with multifactorial inheritance can be defined as traits governed by the ______ effect of multiple genes.
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Not only genetics, but also ______ factors influence multifactorial traits.
Not only genetics, but also ______ factors influence multifactorial traits.
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The ______ of multifactorial inheritance involves both genetic and environmental elements.
The ______ of multifactorial inheritance involves both genetic and environmental elements.
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If the parent cell is ______ (N), then the daughter cells will be haploid.
If the parent cell is ______ (N), then the daughter cells will be haploid.
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The parent cell is designated as ______ (N).
The parent cell is designated as ______ (N).
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The resulting daughter cells will also be ______.
The resulting daughter cells will also be ______.
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Both the parent cell and the daughter cells are ______.
Both the parent cell and the daughter cells are ______.
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In organisms that reproduce sexually, ______ cells undergo meiosis to produce haploid cells.
In organisms that reproduce sexually, ______ cells undergo meiosis to produce haploid cells.
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The aim is to detect birth defects such as ______, Down syndrome, chromosome abnormalities, genetic diseases and other conditions.
The aim is to detect birth defects such as ______, Down syndrome, chromosome abnormalities, genetic diseases and other conditions.
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Diagnostic prenatal testing can be by invasive methods or ______ methods.
Diagnostic prenatal testing can be by invasive methods or ______ methods.
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Down syndrome is one of the conditions detected through ______ prenatal testing.
Down syndrome is one of the conditions detected through ______ prenatal testing.
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Chromosome ______ can lead to various genetic disorders.
Chromosome ______ can lead to various genetic disorders.
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Genetic diseases may also be identified during ______ testing.
Genetic diseases may also be identified during ______ testing.
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Researchers inject genes that are targeted to treat a particular ______ into a patient’s blood stream.
Researchers inject genes that are targeted to treat a particular ______ into a patient’s blood stream.
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When the genes arrive at the site of the defective genes, they produce ______ that can treat the problem.
When the genes arrive at the site of the defective genes, they produce ______ that can treat the problem.
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The genes are injected into the patient’s ______ stream.
The genes are injected into the patient’s ______ stream.
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The process involves targeting ______ genes to address the issue at hand.
The process involves targeting ______ genes to address the issue at hand.
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The goal of these researchers is to produce ______ that can successfully remedy health issues.
The goal of these researchers is to produce ______ that can successfully remedy health issues.
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Study Notes
Genetic Diseases
- Genetic diseases result from mutations in DNA.
- Hereditary disorders are passed from one parent to their offspring through gametes.
- Congenital diseases are present at birth, but not all congenital diseases are genetic.
- Mutations in germ cells are transmitted to offspring, causing inherited diseases.
- Somatic cell mutations are not inherited but can cause cancers and some congenital malformations.
Types of Mutations
- Point mutation: A single nucleotide base is substituted by a different base.
- Example: Sickle cell anemia, where a nucleotide triplet (CTC) is changed to (CAC), altering the amino acid sequence in hemoglobin.
- Missense mutation: A point mutation that changes one amino acid.
- Nonsense mutation: A point mutation that results in a stop codon, prematurely terminating protein synthesis, causing a short peptide that is rapidly degraded.
- Example: B0-thalassemia, where a U substitutes for a C resulting in a premature stop codon.
- Frameshift mutation: Insertion or deletion of one or two base pairs alters the reading frame of the DNA strand.
- Three-base deletion: Doesn't cause a frameshift mutation as it's a multiple of three.
- Example: Cystic fibrosis (CF) allele.
- Four-base insertion: A type of frameshift mutation causing Tay-Sachs disease in Ashkenazi Jews.
- Single-base deletion: A frameshift mutation in the ABO (glycosyltransferase) locus.
Trinucleotide Repeat Mutations
- Characterized by the amplification of a sequence of three nucleotides.
- Example: Fragile X syndrome, which involves a repeating sequence of CGG nucleotides at the FMR-1 gene.
- In the normal population, the number of repetitions is small, around 29. Elevated repeats lead to mental retardation.
Types of Genetic Diseases
- Monogenic diseases (Mendelian): Caused by mutations in a single gene.
- Example: Marfan's syndrome.
- Complex disorders: Involve multiple genes and environmental influences.
- One example is diabetes mellitus.
- Chromosomal disorders: Caused by structural or numerical alterations in autosomes or sex chromosomes.
- Heterogeneous disorders: Involve a single gene but don't follow Mendelian inheritance patterns.
Autosomal Dominant Disorders
- At least one parent of an affected individual is affected.
- Males and females are equally affected.
- Affected individuals have a 50% chance of passing the disorder to each child if an unaffected person is the mate.
- Some patients don't have affected parents, suggesting a new mutation.
- Clinical features can be modified by reduced penetrance or variable expressivity.
- Signs and symptoms may not appear until adulthood.
- Example: Marfan syndrome, hypercholesterolemia, polycystic kidney disease, hereditary spherocytosis, familial polyposis coli.
Autosomal Recessive Disorders
- Manifested only in homozygous state (when both alleles are mutants).
- Trait does not usually affect carriers (heterozygotes).
- Siblings of affected individuals have a 25% risk with each birth.
- Frequency of mutant genes in the population impacts the likelihood of consanguinity.
- Clinical features in this case are more uniform.
- Complete penetrance is more common.
- Onset of signs is usually early in life.
- Example: Sickle cell anemia, thalassemia, glycogen storage disease, cystic fibrosis, phenylketonuria, Wilson disease.
X-linked Disorders
- Most sex-linked diseases are X-linked recessive.
- Only males with the mutated gene on their X chromosome are affected.
- Females are usually silent carriers (they have two X chromosomes, one of which is not carrying the mutated gene)
- Affected males do not pass the disease to their sons, but all daughters are carriers.
- Sons of heterozygous mothers have a 50% chance of inheriting the disease.
- Fewer X-linked dominant disorders exist, where they are transmitted to 50% of sons and daughters of heterozygous females.
- Examples: Hemophilia A and B, glucose-6-phosphate dehydrogenase deficiency, agammaglobulinemia, Duchenne muscular dystrophy.
Diseases Caused by Mutations in Structural Proteins
- Marfan syndrome is an autosomal dominant disease affecting connective tissue (fibrillin).
- Clinical features involve skeletal abnormalities (long limbs, arched palate, etc.), eye problems (lens dislocation), and cardiovascular issues (aortic problems).
- Symptoms often vary between affected individuals.
Diseases Caused by Mutations in Receptor Proteins
- Familial hypercholesterolemia is an autosomal dominant disease affecting LDL receptors in hepatocytes.
- Heterozygotes show elevated plasma cholesterol, and remain asymptomatic until adulthood when xanthomas form.
- Homozygotes have severe disease, with childhood-onset xanthomas and possible premature death.
- Statins are used to treat this disease by increasing LDL receptors, reducing intracellular cholesterol synthesis.
Diseases Caused by Mutations in Enzymes
- Phenylketonuria (PKU) is an inborn error of metabolism.
- In PKU, the enzyme phenylalanine hydroxylase is missing, leading to phenylalanine buildup in the body and mental retardation.
- Infants with PKU usually show a musty odor.
- Treatment involves a restricted phenylalanine diet.
Glycogen Storage Disorders (Glycogenoses)
- An inherited enzyme deficiency affects glycogen synthesis or breakdown.
- Glycogen builds up excessively or abnormally in tissues.
- One variant is Pompe disease, a lysosomal storage disorder.
- Most glycogenoses are autosomal recessive, with varying organ involvement.
- Hepatic form affects the liver, causing enlargement and hypoglycemia.
- Myopathic form affects muscle, causing weakness and cramps.
Diseases Caused by Mutations in Protein That Regulate Cell Growth
- Mutations in oncogenes and tumor suppressor genes.
- Can lead to tumors.
- In 5% of all cancers, mutations affecting tumor suppressor genes are present in all cells of the body, transmissible to their offspring.
- Example: Neurofibromatoses type 1 & 2.
- NF1 (Chromosome 17): Encodes a protein acting as a negative regulator.
- NF2 (Chromosome 22): Rarity, Café-au-lait spots, bilateral acoustic neuroma.
Numerical Abnormalities
- Normal chromosome count in humans is 46 (2n=46).
- Chromosomal number multiples of this haploid number are termed euploid.
- Chromosomal numbers that are not exact multiples are called aneuploid.
- Aneuploidy is mainly caused by non-disjunction in meiosis (failure of chromosomes to separate).
- Non-disjunction during meiosis leads to gametes with extra chromosomes (n+1) or fewer chromosomes (n-1).
- During fertilization, this results in trisomy (2n+1) or monosomy (2n-1).
- Examples: Trisomy 21 (Down syndrome), trisomy 18 and trisomy 13 (Patau syndrome).
Structural Abnormalities
- Involve chromosome breakage and rearrangement.
- Translocation: A part of one chromosome is transferred to another.
- Example: Philadelphia chromosome (t(9;22))
- Isochromosomes: One arm of a chromosome is duplicated, and the other is lost.
- Deletions: Involve loss of a chromosome segment.
- Example: Cri-du-chat syndrome. Inversions: A chromosome segment is reversed.
- Ring chromosomes: A chromosome forms a ring shape due to deletion at each end.
Cytogenetic Disorders Involving Sex Chromosomes
- Most are tolerated more readily than autosomal abnormalities.
- Lyonization (X chromosome inactivation) and the limited genetic information of the Y chromosome contribute to this tolerance.
- Examples: Klinefelter syndrome (47,XXY), XYY males, Turner syndrome (45, XO).
Single-Gene Disorders With Atypical Inheritance Patterns
- Some diseases resulting from single-gene mutations do not follow Mendelian inheritance.
- Fragile X syndrome is an example of a disease with this atypical pattern of inheritance.
- The mutation length of a trinucleotide repeat sequence(CGG) correlates with clinical severity.
Diseases Caused by Mitochondrial Genes
- Mitochondrial genes are maternally inherited.
- Examples are rare and can include progressive bilateral vision loss.
Prenatal Testing
- Testing for fetal conditions pre-birth; for example:
- Amniocentesis (sampling amniotic fluid).
- Chorionic villus sampling (sampling tissues).
Postnatal Genetic Analysis
- Genetic testing for conditions detected at birth, such as developmental problems; or later in life, such as infertility.
Genetic Counseling
- Genetic counseling provides information to couples about potential risks to their children.
- This type of support is for couples who have a previously affected child or carrier genes.
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Description
This quiz explores key concepts related to enzyme activity, nonenzyme proteins, and the regulation of metabolic pathways. Understand the role of genes in metabolism and the impact of genetic disorders on health. Test your knowledge on multifactorial traits and the interplay between genetic and environmental factors.
