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Genetics Flashcards

General genetic principles

1
Q

What does the central dogma of genetics outline?

A

The flow of genetic information in living organisms: DNA → RNA → Protein

This includes replication, transcription, and translation processes.

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2
Q

What is replication in the context of the central dogma?

A

DNA is duplicated to ensure genetic material is inherited by daughter cells during cell division.

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3
Q

What occurs during transcription?

A

DNA is transcribed into RNA (specifically, mRNA) by RNA polymerase in the nucleus.

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4
Q

What are promoters?

A

Regions of DNA that signal RNA polymerase to start transcription.

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5
Q

Differentiate between exons and introns.

A

Exons are coding regions of mRNA; introns are spliced out.

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6
Q

What is the role of tRNA in translation?

A

Delivers amino acids to the ribosome.

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7
Q

What are codons?

A

Groups of three nucleotides in mRNA that encode specific amino acids.

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8
Q

What is the start codon and what does it initiate?

A

AUG (methionine) initiates protein translation.

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9
Q

List the stop codons.

A
  • UAA
  • UAG
  • UGA
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10
Q

What is the genetic code?

A

A set of rules dictating how nucleotide sequences in mRNA are translated into proteins.

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11
Q

What are the key features of the genetic code?

A
  • Universal
  • Degenerate
  • Non-overlapping
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12
Q

Define mutation.

A

A permanent change in the DNA sequence that can affect protein function.

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13
Q

What is a point mutation?

A

A single nucleotide substitution.

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14
Q

What is a silent mutation?

A

No change in the encoded amino acid (e.g., CUU → CUC, both encode leucine).

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15
Q

What is a missense mutation?

A

Changes the amino acid (e.g., Glu → Val in sickle cell anemia).

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16
Q

What is a nonsense mutation?

A

Converts a codon into a stop codon (e.g., UGC → UGA).

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17
Q

What are frameshift mutations caused by?

A

Insertion or deletion of nucleotides not in multiples of three, disrupting the reading frame.

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18
Q

Provide an example of a frameshift mutation.

A

Adding one nucleotide to AUG-CUU becomes AUC-UUC, altering all downstream amino acids.

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19
Q

What are trinucleotide repeat disorders?

A

Disorders caused by the abnormal expansion of three-nucleotide sequences within or near genes.

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20
Q

What happens in normal individuals regarding trinucleotide repeats?

A

They have stable numbers of repeats, but expanded repeats cause disease.

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21
Q

List examples of trinucleotide repeat disorders.

A
  • Huntington’s disease
  • Fragile X syndrome
  • Myotonic dystrophy
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22
Q

Define anticipation in genetics.

A

A phenomenon where a genetic disorder worsens or manifests earlier in subsequent generations due to repeat expansions.

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23
Q

Provide examples of diseases that exhibit anticipation.

A
  • Huntington’s disease
  • Myotonic dystrophy
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24
Q

How does paternal inheritance affect Huntington’s disease?

A

It leads to earlier onset of the disease.

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25
How does maternal transmission affect myotonic dystrophy?
The severity increases with maternal transmission.
26
What is a gene?
A DNA sequence encoding a protein or functional RNA.
27
What is a locus?
A gene's location on a chromosome.
28
What is an allele?
Variant forms of a gene.
29
What is a genotype?
The genetic makeup of an individual.
30
What is a phenotype?
Observable traits resulting from genotype-environment interactions.
31
What does homozygous mean?
Possessing two identical alleles (e.g., AA or aa).
32
What does heterozygous mean?
Possessing two different alleles (e.g., Aa).
33
What does dominant mean?
A trait expressed with one allele (e.g., Aa or AA).
34
What does recessive mean?
A trait expressed only with two identical alleles (e.g., aa).
35
What is autosomal dominant inheritance?
Requires only one mutated allele for the phenotype.
36
What are examples of autosomal dominant disorders?
Marfan syndrome, Huntington’s disease.
37
What is the recurrence risk for autosomal dominant disorders?
50% if one parent is affected.
38
What is autosomal recessive inheritance?
Requires two mutated alleles for the phenotype.
39
What are examples of autosomal recessive disorders?
Cystic fibrosis, sickle cell anemia.
40
What is the recurrence risk for autosomal recessive disorders?
25% if both parents are carriers.
41
What is X-linked dominant inheritance?
Affects males and females.
42
What are examples of X-linked dominant disorders?
Rett syndrome, hypophosphatemic rickets.
43
What is X-linked recessive inheritance?
Affects males more severely; females are carriers.
44
What are examples of X-linked recessive disorders?
Hemophilia A, Duchenne muscular dystrophy.
45
What is the recurrence risk for sons of carrier mothers in X-linked recessive disorders?
Sons have a 50% chance of being affected.
46
What are the properties of mitochondrial inheritance?
Inherited exclusively from the mother.
47
What tissues are affected by mitochondrial inheritance?
Affects tissues requiring high energy (e.g., brain, muscles).
48
What are examples of mitochondrial disorders?
Leber hereditary optic neuropathy (LHON), MELAS syndrome.
49
What is incomplete penetrance?
Not all individuals with a mutation exhibit symptoms (e.g., BRCA1 mutation carriers).
50
What is pleiotropy?
A single gene mutation impacts multiple systems (e.g., Marfan syndrome affects connective tissue, heart, and eyes).
51
What is genetic imprinting?
Differential expression of genes depending on their parental origin.
52
What is uniparental disomy?
Both chromosomes come from one parent.
53
What is an example of Prader-Willi syndrome?
Paternal deletion on chromosome 15 or maternal uniparental disomy.
54
What is an example of Angelman syndrome?
Maternal deletion on chromosome 15 or paternal uniparental disomy.
55
What is genotype frequency?
The proportion of individuals in a population with a specific genotype, expressed as a fraction or percentage of the total population.
56
How is genotype frequency mathematically expressed?
f(Genotype) = Number of individuals with a specific genotype / Total number of individuals in the population.
57
What does allele frequency measure?
The proportion of a specific allele among all alleles at a particular locus in the population.
58
Why is allele frequency important?
It measures genetic diversity within a population.
59
How is allele frequency calculated for two alleles (A and a)?
f(A) = [2(AA) + (Aa)] / 2N, f(a) = [2(aa) + (Aa)] / 2N.
60
Calculate the genotype frequency for AA in a population of 100 individuals with 25 AA.
f(AA) = 25 / 100 = 0.25.
61
Calculate the allele frequency for allele A given 25 AA and 50 Aa in a population of 100.
f(A) = [2(25) + 50] / 200 = 0.5.
62
What is the definition of Hardy-Weinberg Equilibrium (HWE)?
A theoretical state where allele and genotype frequencies in a population remain constant from generation to generation under certain assumptions.
63
List the key assumptions of Hardy-Weinberg Equilibrium.
* Large population size * No mutation * Random mating * No natural selection * No gene flow.
64
What does a deviation from Hardy-Weinberg equilibrium indicate?
It indicates that one or more of the assumptions may be violated, signaling evolutionary change.
65
What is the Hardy-Weinberg equation for a single gene with two alleles?
p² + 2pq + q² = 1.
66
What does p² represent in the Hardy-Weinberg equation?
Frequency of homozygous dominant genotype (AA).
67
What is the formula to estimate genotype frequencies using Hardy-Weinberg equilibrium?
Given allele frequencies p and q, use f(AA) = p², f(Aa) = 2pq, f(aa) = q².
68
Given p = 0.6 and q = 0.4, what is f(Aa)?
f(Aa) = 2pq = 2(0.6)(0.4) = 0.48.
69
Define genetic variation.
The diversity of alleles and genotypes within a population.
70
What are the factors that contribute to genetic variation?
* Mutation * Genetic recombination * Gene flow (migration) * Genetic drift * Natural selection * Non-random mating * Population size * Environmental factors.
71
What is the role of mutation in genetic variation?
It introduces new alleles and is the ultimate source of all genetic variation.
72
How does genetic recombination contribute to genetic variation?
Homologous chromosomes exchange genetic material during meiosis, creating new allele combinations.
73
What is genetic drift?
Random changes in allele frequencies that can lead to loss of genetic variation, especially in small populations.
74
True or False: Natural selection can increase or decrease genetic variation.
True.
75
How does population size affect genetic variation?
Larger populations tend to maintain more genetic variation due to reduced effects of genetic drift.
76
What environmental factors influence genetic variation?
Selective pressures such as climate, predators, or food availability.
77
What is a karyotype?
A display of an individual’s complete set of chromosomes arranged in pairs and sorted by size, centromere position, and banding pattern ## Footnote Chromosomes are visualized using stains (e.g., Giemsa stain for G-banding).
78
What does a normal karyotype include?
22 pairs of autosomes and 1 pair of sex chromosomes
79
What is the notation for a normal female's karyotype?
46,XX
80
What does 47,XX,+21 represent?
A female with trisomy 21 (Down syndrome)
81
What does 46,XY,t(9;22) indicate?
A male with translocation between chromosomes 9 and 22 (Philadelphia chromosome, associated with chronic myeloid leukemia)
82
What are numerical chromosomal abnormalities?
Variations in chromosome number due to errors in cell division (nondisjunction or anaphase lag)
83
Define euploidy.
A normal set of chromosomes (e.g., 46 in humans)
84
Define aneuploidy.
Gain or loss of chromosomes
85
What are the clinical features of Trisomy 21 (Down syndrome)?
Intellectual disability, hypotonia, characteristic facial features, congenital heart defects
86
What are the clinical features of Trisomy 18 (Edwards syndrome)?
Severe developmental delays, overlapping fingers, rocker-bottom feet
87
What are the clinical features of Trisomy 13 (Patau syndrome)?
Microcephaly, cleft lip/palate, polydactyly, congenital heart defects
88
What is Turner syndrome?
Monosomy of the X chromosome in females (45,X)
89
What are the clinical features of Turner syndrome?
Short stature, gonadal dysgenesis, webbed neck
90
What is Klinefelter syndrome?
Extra X chromosome in males (47,XXY)
91
What are the clinical features of Klinefelter syndrome?
Tall stature, hypogonadism, gynecomastia, infertility
92
What is the most common cause of numerical chromosomal abnormalities?
Nondisjunction during meiosis
93
What is nondisjunction?
Failure of homologous chromosomes (meiosis I) or sister chromatids (meiosis II) to separate
94
What are structural chromosomal abnormalities?
Result from chromosomal breakage and improper repair
95
What is translocation in terms of chromosomal abnormalities?
Exchange of segments between non-homologous chromosomes
96
What is Robertsonian translocation?
Fusion of two acrocentric chromosomes (e.g., t(14;21) associated with hereditary Down syndrome)
97
What is deletion in chromosomal abnormalities?
Loss of a chromosome segment
98
What syndrome is associated with a 5p deletion?
Cri-du-chat syndrome
99
What is inversion in chromosomal abnormalities?
A chromosome segment is reversed end-to-end
100
What is a paracentric inversion?
Does not involve the centromere
101
What is a pericentric inversion?
Includes the centromere
102
What is a ring chromosome?
A circular chromosome formed when the ends fuse after breakage
103
What condition is associated with a ring X chromosome?
Turner syndrome
104
What is multifactorial inheritance?
Results from the combined effect of multiple genes (polygenic) and environmental factors. ## Footnote Multifactorial inheritance is key in understanding common diseases where both genetic and environmental factors play a role.
105
Name an example of a multifactorial disease influenced by genetic predisposition and lifestyle factors.
Type 2 diabetes ## Footnote Obesity and diet are significant lifestyle factors impacting the risk of developing Type 2 diabetes.
106
What is the relationship between hypertension and multifactorial inheritance?
Genetic susceptibility combined with environmental triggers. ## Footnote Environmental factors like salt intake and stress can significantly influence the development of hypertension.
107
List two examples of congenital diseases that are multifactorial.
* Cleft lip/palate * Neural tube defects (e.g., spina bifida) ## Footnote These conditions arise from the interplay of genetic and environmental factors during development.
108
What does the multifactorial threshold model explain?
The likelihood of developing a multifactorial disease. ## Footnote This model helps to understand how genetic and environmental factors contribute to disease risk.
109
Under the threshold model, when does disease occur?
When the combined genetic and environmental factors surpass a certain threshold. ## Footnote This threshold varies among individuals and populations.
110
How does the threshold for disease expression differ?
It varies between sexes and populations. ## Footnote For example, some diseases may express more frequently in one sex due to differing thresholds.
111
Give an example of a condition that shows a lower threshold for expression in males.
Pyloric stenosis ## Footnote This condition occurs more frequently in males, suggesting they require fewer risk factors to express the disease.
112
What factors influence the assessment of recurrence risk for multifactorial diseases?
* Number of affected relatives * Severity of the condition in the proband * Closeness of the familial relationship * Population prevalence ## Footnote These factors are crucial in estimating the likelihood of recurrence in families with a history of multifactorial diseases.
113
How does folic acid supplementation impact the risk of neural tube defects?
Decreases the risk ## Footnote Adequate folic acid intake is known to significantly lower the risk of certain congenital defects.
114
What increases the recurrence risk of neural tube defects?
Maternal history of the defect. ## Footnote A family history of neural tube defects serves as a significant risk factor for future pregnancies.
115
What is genetic analysis?
Studying DNA, RNA, and protein to identify mutations and chromosomal abnormalities ## Footnote Includes cytogenetic techniques, molecular techniques, and biochemical analysis.
116
What are cytogenetic techniques used in genetic analysis?
Karyotyping, fluorescence in situ hybridization (FISH) ## Footnote These techniques help visualize chromosomal abnormalities.
117
What are molecular techniques used in genetic analysis?
PCR, next-generation sequencing (NGS), microarrays ## Footnote These methods analyze DNA and RNA sequences for mutations.
118
What does biochemical analysis in genetic analysis involve?
Enzyme assays to detect metabolic abnormalities ## Footnote Helps in identifying biochemical defects associated with genetic disorders.
119
What is the purpose of a Southern blot?
Detects specific DNA sequences ## Footnote Used for large gene rearrangements, such as in Duchenne muscular dystrophy.
120
What does a Northern blot analyze?
RNA to study gene expression ## Footnote Example: Detection of gene silencing in Fragile X syndrome.
121
What is the function of a Western blot?
Detects specific proteins ## Footnote Example: Diagnosing HIV through detection of viral proteins.
122
What is the polymerase chain reaction (PCR)?
A technique that amplifies specific DNA sequences using primers and a thermostable DNA polymerase ## Footnote Commonly uses Taq polymerase.
123
List the steps of PCR.
* Denaturation * Annealing * Extension ## Footnote Each step plays a crucial role in amplifying the target DNA sequence.
124
What are some applications of PCR?
* Detecting mutations (e.g., BRCA1/2 mutations in breast cancer) * Pathogen detection (e.g., HIV, SARS-CoV-2) ## Footnote PCR is widely used in clinical diagnostics.
125
What types of tests are included in prenatal screening?
* Non-invasive tests (e.g., ultrasound, cell-free DNA) * Invasive tests (e.g., amniocentesis, chorionic villus sampling) ## Footnote These tests help identify genetic disorders before birth.
126
What is the purpose of newborn screening?
To detect treatable conditions shortly after birth ## Footnote Early detection enables timely intervention.
127
Provide examples of conditions screened in newborns.
* Phenylketonuria (PKU) * Congenital hypothyroidism * Sickle cell disease ## Footnote Each of these conditions has specific testing methods and treatment protocols.
128
Fill in the blank: PCR amplifies specific DNA sequences using _______.
[primers and a thermostable DNA polymerase]
129
What are the major steps involved in recombination or analysis in the lab?
1. Preparation of DNA samples 2. Digestion with restriction enzymes 3. Gel electrophoresis 4. Transfer to membrane 5. Hybridization with probes 6. Visualization of results ## Footnote These steps are crucial for analyzing DNA fragments and their recombination.
130
How do restriction endonucleases know where to cut the DNA?
They recognize specific sequences of nucleotides ## Footnote Restriction endonucleases are enzymes that cut DNA at specific sites, which are usually palindromic sequences.
131
What are DNA fragments?
Short pieces of DNA produced by cutting longer strands with enzymes ## Footnote Fragments are essential for analysis in techniques like gel electrophoresis.
132
What is the role of a probe in genetic analysis?
To hybridize with specific DNA sequences for visualization ## Footnote Probes are typically labeled with radioactive or fluorescent tags for detection.
133
What are the different types of blotting techniques?
* Southern blotting * Northern blotting * Western blotting ## Footnote Each type of blotting is used for different macromolecules: DNA, RNA, and proteins respectively.
134
What does PCR stand for?
Polymerase Chain Reaction ## Footnote PCR is a technique used to amplify specific DNA sequences.
135
What are the key chemicals needed for PCR?
* DNA template * DNA polymerase * Primers * Nucleotides * Buffer ## Footnote These components are essential for the PCR process to occur effectively.
136
What are the steps involved in the Polymerase Chain Reaction (PCR)?
1. Denaturation 2. Annealing 3. Extension ## Footnote These steps are repeated for multiple cycles to amplify the target DNA.
137
What is genetic screening?
The process of testing individuals for specific genetic conditions ## Footnote Screening can be done at various life stages including preconception, prenatal, and newborn.
138
What is involved in first trimester screening?
Testing for genetic conditions in the first three months of pregnancy ## Footnote This typically includes blood tests and ultrasound measurements.
139
What does second trimester screening involve?
Testing between 3 to 6 months of pregnancy for genetic conditions ## Footnote This may involve different tests compared to the first trimester.
140
What is the importance of interpreting test results in genetic screening?
To determine the likelihood of genetic disorders ## Footnote Accurate interpretation is crucial for making informed medical decisions.
141
What approach is used for fetal screening?
Analysis of maternal blood and ultrasound imaging ## Footnote These methods help assess fetal health and detect potential genetic issues.
142
What is cell free DNA (cfDNA) analysis?
Analyzing fragments of DNA that are released into the maternal bloodstream ## Footnote cfDNA can provide insights into the genetic makeup of the fetus.
143
What is newborn screening?
Testing newborns for certain genetic disorders shortly after birth ## Footnote This allows for early detection and intervention for treatable conditions.
144
What is the term for inheritance influenced by multiple factors?
Multifactorial Inheritance
145
What model explains the inheritance of multifactorial diseases?
Multifactorial Threshold Model
146
True or False: The threshold model can be the same for males and females.
False
147
What is assessed to understand the likelihood of recurrence for multifactorial diseases?
Recurrence Risks
148
Fill in the blank: Congenital Malformations are examples of _______.
common diseases
149
List two diseases associated with multifactorial inheritance.
* Heart Disease * Hypertension
150
Define karyotype.
The number and appearance of chromosomes in the nucleus of a cell ## Footnote Karyotyping is often used in genetic testing.
151
What is euploidy?
The condition of having a complete set of chromosomes ## Footnote It contrasts with aneuploidy.
152
What is aneuploidy?
The presence of an abnormal number of chromosomes in a cell ## Footnote This can lead to various genetic disorders.
153
What are common causes for aneuploidy?
Errors during cell division, specifically meiosis ## Footnote These errors can lead to gametes with abnormal chromosome numbers.
154
What is Trisomy 21 also known as?
Down Syndrome ## Footnote It is characterized by an extra chromosome 21.
155
What is the karyotype for Trisomy 18?
47,XY,+18 or 47,XX,+18 ## Footnote This condition is also known as Edward Syndrome.
156
What is Trisomy 13 also referred to as?
Patau Syndrome ## Footnote It is associated with severe intellectual disability and physical abnormalities.
157
What is sex chromosome aneuploidy?
Aneuploidy involving the sex chromosomes ## Footnote This can lead to syndromes like Klinefelter and Turner Syndrome.
158
What is Klinefelter Syndrome's karyotype?
47,XXY ## Footnote This condition affects males and can result in infertility.
159
What is the karyotype for Turner Syndrome?
45,X or 45,XO ## Footnote This condition affects females and leads to various developmental issues.
160
Define genetic mosaicism in Turner Syndrome.
A condition where some cells have the typical 46 chromosomes and others have 45 ## Footnote This can result in varied symptoms.
161
What are structural chromosomal abnormalities?
Changes in the structure of chromosomes ## Footnote These include deletions, duplications, inversions, and translocations.
162
What is translocation?
A chromosomal segment is moved from one chromosome to another ## Footnote This can be reciprocal or Robertsonian.
163
What is a reciprocal translocation?
A mutual exchange of segments between two chromosomes ## Footnote This may not always result in a genetic disorder.
164
Define Robertsonian translocation.
A type of chromosomal translocation involving the fusion of two acrocentric chromosomes ## Footnote This can lead to Down syndrome in some cases.
165
How is Down syndrome related to Robertsonian translocation?
Certain Robertsonian translocations can lead to an extra chromosome 21 ## Footnote This is one of the ways Down syndrome can occur.
166
What are some important translocations?
Translocations associated with various cancers and genetic disorders ## Footnote Examples include the Philadelphia chromosome in chronic myelogenous leukemia.
167
What is a deletion in cytogenetics?
Loss of a chromosome segment ## Footnote This can lead to genetic disorders depending on the genes lost.
168
What are some examples of deletions or microdeletions?
Cri du chat syndrome, 22q11.2 deletion syndrome ## Footnote These conditions result from specific deletions on chromosomes.
169
What is an inversion in chromosomal structure?
A segment of a chromosome is reversed end to end ## Footnote This can disrupt gene function but may not always cause a disorder.
170
Define ring chromosome.
A chromosome that forms a ring due to the fusion of its ends ## Footnote This can lead to various genetic anomalies.
171
What is the primary focus of population genetics?
The study of genetic variation within populations and the factors that influence this variation.
172
Define genotype frequency.
The proportion of a specific genotype among all genotypes in a population.
173
Define allele frequency.
The proportion of a specific allele among all alleles in a population.
174
What is Hardy-Weinberg Equilibrium?
A principle that describes the genetic variation of a population that is not evolving.
175
List the assumptions for Hardy-Weinberg equilibrium.
* No mutations * Random mating * No natural selection * Extremely large population size * No gene flow
176
What is the Hardy-Weinberg equation?
p² + 2pq + q² = 1
177
What does p represent in the Hardy-Weinberg equation?
The frequency of the dominant allele.
178
What does q represent in the Hardy-Weinberg equation?
The frequency of the recessive allele.
179
How is Hardy-Weinberg equilibrium applied to autosomal recessive disorders?
It can predict the frequency of carriers and affected individuals in a population.
180
What role does Hardy-Weinberg equilibrium play in X-linked recessive diseases?
It helps in estimating the prevalence of these diseases in a population.
181
What are the factors causing genetic variation in populations?
* Mutation * Natural selection * Genetic drift * Gene flow
182
Define mutation in the context of population genetics.
A change in the DNA sequence that can lead to genetic variation.
183
What is natural selection?
The process where organisms better adapted to their environment tend to survive and produce more offspring.
184
Define genetic drift.
Random fluctuations in allele frequencies due to chance events.
185
What is gene flow?
The transfer of genetic variation from one population to another.
186
True or False: Hardy-Weinberg equilibrium suggests that populations will always remain in equilibrium.
False.
187
What is the definition of a single gene disorder?
A disorder caused by mutations in a single gene ## Footnote Single gene disorders can be inherited in various patterns such as autosomal dominant, autosomal recessive, and X-linked.
188
What are the types of inheritance patterns for single gene disorders?
* Autosomal Dominant (AD) * Autosomal Recessive (AR) * X-linked * Mitochondrial inheritance
189
What is a pedigree?
A diagram that depicts the biological relationships between individuals in a family ## Footnote Pedigrees are used to track inheritance patterns of traits or disorders.
190
What is an example of an autosomal dominant disorder?
Huntington's disease ## Footnote Other examples include Marfan syndrome and achondroplasia.
191
What is the recurrence risk for autosomal dominant disorders?
50% chance of passing the disorder to offspring ## Footnote This is because only one copy of the mutated gene is needed for the disorder to manifest.
192
What is co-dominance?
A genetic scenario where both alleles in a heterozygote are fully expressed ## Footnote An example is the ABO blood group system.
193
What is an example of an autosomal recessive disorder?
Cystic fibrosis ## Footnote Other examples include sickle cell anemia and Tay-Sachs disease.
194
What is the recurrence risk for autosomal recessive disorders?
25% chance of having an affected child if both parents are carriers ## Footnote This occurs because two copies of the mutated gene are needed for the disorder to manifest.
195
How does consanguinity affect the risk of autosomal recessive disorders?
Increases the likelihood of both parents being carriers ## Footnote This can lead to a higher incidence of recessive disorders in offspring.
196
What is an X-linked gene disorder?
A disorder caused by mutations on the X chromosome ## Footnote These disorders often affect males more severely than females.
197
What is an example of an X-linked recessive disorder?
Hemophilia ## Footnote Other examples include Duchenne muscular dystrophy.
198
What is the recurrence risk for X-linked recessive disorders?
50% chance for male offspring to be affected if the mother is a carrier ## Footnote Female offspring have a 50% chance of being carriers.
199
What is X-inactivation?
The process by which one X chromosome in females is randomly inactivated ## Footnote This helps to balance gene dosage between males and females.
200
What is an example of an X-linked dominant disorder?
Fragile X syndrome ## Footnote Other examples include Rett syndrome.
201
What is the recurrence risk for X-linked dominant disorders?
50% chance of passing the disorder to offspring ## Footnote This risk applies to both male and female offspring if the affected parent is female.
202
What is mitochondrial inheritance?
Inheritance of traits determined by genes in mitochondria ## Footnote Mitochondrial disorders are typically passed from mother to offspring.
203
What is incomplete penetrance?
The phenomenon where not all individuals with a mutation express the disorder ## Footnote This can lead to variability in the manifestation of genetic conditions.
204
What is pleiotropy?
A single gene influencing multiple phenotypic traits ## Footnote An example is Marfan syndrome, which affects connective tissue and has multiple manifestations.
205
What is imprinting in genetics?
A process where genes are expressed in a parent-of-origin-specific manner ## Footnote This can lead to disorders if the imprinted gene is mutated.
206
What are examples of disorders associated with imprinting?
* Prader-Willi syndrome * Angelman syndrome
207
What is uniparental disomy?
A condition where both copies of a chromosome are inherited from one parent ## Footnote This can lead to disorders due to the absence of genes from the other parent.
208
What is the Central Dogma of Genetics?
The framework explaining the flow of genetic information from DNA to RNA to protein ## Footnote It outlines the processes of transcription and translation.
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What are codons?
Sequences of three nucleotides that specify an amino acid ## Footnote Codons are crucial for translating the genetic code into proteins.
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What is the genetic code?
The set of rules by which information encoded in genetic material is translated into proteins ## Footnote It includes codons that correspond to specific amino acids.
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What are the different types of codons?
There are three main types of codons: * Start codons * Stop codons * Sense codons ## Footnote Start codons initiate translation, stop codons terminate it, and sense codons correspond to amino acids.
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What is a mutation?
A change in the DNA sequence that can lead to alterations in protein function ## Footnote Mutations can occur naturally or be induced by environmental factors.
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What are the types of mutations?
Mutations can be classified as: * Point mutations * Insertions * Deletions * Duplications ## Footnote Each type has different effects on the genetic sequence and protein produced.
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What are trinucleotide repeat disorders?
Genetic disorders caused by the repetition of specific three-nucleotide sequences ## Footnote These disorders often lead to neurodegenerative diseases.
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What is Huntington’s disease?
A genetic disorder characterized by progressive neurodegeneration ## Footnote It is caused by expanded CAG repeats in the HTT gene.
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What is anticipation in genetics?
The phenomenon where genetic disorders become more severe or appear at an earlier age in successive generations ## Footnote This is often observed in trinucleotide repeat disorders.
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Fill in the blank: The Central Dogma of Genetics describes the flow of information from _______ to RNA to protein.
DNA
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True or False: All mutations lead to harmful effects on the organism.
False ## Footnote Some mutations can be neutral or even beneficial.
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A mutation that adds the codon UAG into a gene sequence will have what effect?
This will be a nonsense mutation
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[Blank] is seen in diseases that involve trinucleotide repeat expansions (e.g., Huntington's Disease).
Anticipation ## Footnote Anticipation involves repeating codons that increase and result in more severe disease with each successive generation.
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What is the function of nucleotide excision repair?
It removes damaged bases, allowing DNA polymerase to add new bases, and ligase links them to the old chain.
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During which cell cycle phase does nucleotide excision repair occur?
G1 phase.
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What type of DNA damage does nucleotide excision repair fix?
Bulky defects that distort the DNA helix, such as pyrimidine dimers caused by UVA and UVB radiation.
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What genetic disorder is associated with defective nucleotide excision repair?
Xeroderma Pigmentosum (XP).
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What are the symptoms of Xeroderma Pigmentosum?
Sunlight intolerance, skin cancer, actinic keratoses, corneal ulcers.
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What enzyme initiates base excision repair?
Glycosylase, which excises the damaged base and creates an AP site.
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What enzymes are involved in base excision repair?
* AP-endonuclease: Cleaves the 5' end to remove nucleotides. * Lyase: Cleaves the 3' end. * DNA Polymerase-B: Adds undamaged nucleotides. * Ligase: Links the nucleotides together.
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During which phases of the cell cycle does base excision repair occur?
Throughout the entire cell cycle.
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What diseases are associated with defective base excision repair?
* Some cancers. * Neurological disorders. * Familial Adenomatous Polyposis (FAP): Autosomal dominant defect in the APC gene, leading to colon cancer at a young age.
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What type of mutations does mismatch repair correct?
G/T or A/C mismatches during DNA replication.
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What enzymes are involved in mismatch repair?
MutS, MutH, MutL enzymes at the S phase checkpoint.
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How does mismatch repair work?
* MSH proteins identify mismatched bases in the daughter strand. * Endonuclease breaks the strand. * Exonuclease removes incorrect bases. * DNA polymerase adds correct bases. * DNA ligase reseals the DNA strand.
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What genetic disorder is caused by defective mismatch repair?
Lynch Syndrome (Hereditary Non-Polyposis Colorectal Cancer, HNPCC).
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What genetic mutations are associated with Lynch Syndrome?
MLH1 or MSH2 gene mutations.
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What molecular marker is associated with Lynch Syndrome?
Microsatellite instability (unstable repeating di- or trinucleotides). ## Footnote Autosomal dominant mutation in MLH1 or MSH2 genes which leads to decreased mismatch repair.
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What is homologous recombination in DNA repair?
It is a repair mechanism that uses a sister chromatid as a template to repair double-strand breaks, ensuring no loss of DNA and more accurate repairs, occurring in the late S phase/G2 of the cell cycle.
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What are the key mutations associated with defective homologous recombination?
BRCA1 mutation → Defective homologous recombination → Breast/Ovarian Cancer BLM mutation → Defective homologous recombination → Bloom Syndrome
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What are the clinical features of Bloom Syndrome?
Short stature, narrow face, red rash, increased risk of skin cancer.
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What is Fanconi Anemia, and what are its clinical manifestations?
A disorder associated with defective homologous recombination, leading to: * Aplastic anemia * Bone marrow failure * Skeletal abnormalities * Acute Myeloid Leukemia (AML) * Café-au-lait spots * Kidney abnormalities * Intellectual disability * Hydrocephalus
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What is Nonhomologous End Joining (NHEJ) in DNA repair?
A repair mechanism that directly reanneals two DNA fragments without a template, occurring throughout the cell cycle but with an increased risk of errors.
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How does Nonhomologous End Joining (NHEJ) differ from homologous recombination?
Unlike homologous recombination, NHEJ does not require a homologous template and is more error-prone. It is used when no sister chromatid is available.
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What types of DNA damage are repaired by Nonhomologous End Joining (NHEJ)?
Ionizing radiation-induced breaks Oxidative free radical damage Radiation-induced DNA damage
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What genetic disorder is associated with defective Nonhomologous End Joining (NHEJ)?
Ataxia Telangiectasia (AR, ATM mutation)
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What are the clinical features of Ataxia Telangiectasia?
Ataxia (loss of coordination) Telangiectasias (small dilated blood vessels) Spider angiomas Sinopulmonary infections (due to IgA deficiency) Increased Alpha-fetoprotein (AFP) Decreased IgA, IgG, and IgE

General Principles of Medicine (11 decks)

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