20 Questions
Which term describes the number of sets of chromosomes in a cell?
Diploid
What is the term for the specific location of a gene on a chromosome?
Loci
Why does Mendelian genetics not easily apply to many diseases?
De novo mutations and multiple loci can influence disease inheritance
What is the term used to describe the proportion of individuals with the disease-causing variant that have the disease phenotype?
Penetrance
Which type of mutations are mostly observed for autosomal dominant variants and occur in germline cells, which can be inherited in offspring?
De Novo Mutations
What term is used to describe the presence of a disease without any family history of the disease, with low recurrence risk in siblings if not in progenitor germline cells?
De Novo Mutations
What is the term used to describe the multiple loci variants (not alleles) of the disease-causing genes?
Allelic Heterogeneity
Which term refers to the variants upon variants that are observed in diseases such as hemophilia A, Duchenne muscular dystrophy, and osteogenesis imperfecta type II?
De Novo Mutations
What did Mendel's first law, the law of segregation, describe?
The random union of gametes during fertilization
What do sex chromosomes consist of in humans?
1 pair, with females having XX and males having XY
What does the law of independent assortment describe?
Genes at different loci are transmitted independently
During which phase of meiosis does crossing over of segments between homologs occur?
Prophase I
What is the result of cytokinesis in oogenesis?
Unequal division resulting in the ejection of one nucleus (polar body) per meiotic division
What is the role of interkinesis in meiosis?
Phase between meiosis I and meiosis II involving centriole replication and reorganization of centromere/kinetochore
What is the frequency of autosomal recessive genes in the population?
2%
What is consanguinity and its impact on autosomal recessive diseases?
Consanguinity refers to reproductive unions between related persons and increases the probability of autosomal recessive diseases.
What is the inheritance pattern of autosomal recessive genes?
It involves skipping generations and has equal proportion in male and female offspring.
Which statement about autosomal dominant diseases is most accurate?
They can occur through spontaneous germline mutations, more frequent than autosomal recessive diseases.
What is a characteristic of monogenic character diseases?
They exhibit gene dosage effects, giving three possible phenotypes from the genotypes.
What is a key factor in the inheritance pattern of autosomal dominant diseases?
They are observed in every generation with equal proportion in male and female offspring.
Study Notes
Autosomal Dominant and Recessive Inheritance Patterns
- Monogenic character diseases have genes at one locus with 2 possible alleles, and can be dominant or recessive, with multiple variants within the gene, such as ABO blood type alleles
- Polygenic character diseases have genes at multiple loci with each having 2 or more possible alleles, with disease phenotype dependent upon the combination of alleles
- Mendelian genetics assumes a binary relationship between genotype and phenotype, with dominant or recessive traits for a character
- Gene dosage effects for monogenic diseases may give three possible phenotypes from the genotypes
- Autosomal dominant diseases have a frequency of about 5/1000, with specific diseases having low frequency in the population, and inheritance patterns observed in every generation with equal proportion in male and female offspring
- Variant gene products for autosomal dominant diseases can be gain of function, dominant negative, non-functional, or non-functional with non-disease form being an inhibitor of disease development
- Autosomal dominant diseases can occur through spontaneous germline mutations, more frequent than autosomal recessive diseases
- Homozygote disease phenotype is generally more severe than heterozygote for autosomal dominant diseases
- Achondroplasia is an example of autosomal dominant disease, with a clinical phenotype of short limb dwarfism with macrocephaly, kyphosis, midfacial retrusion, and genetics associated with a point mutation in FGF3R gene resulting in altered protein aa sequence
- Over 80% of achondroplasia cases occur via spontaneous germline mutations, with nearly all germline mutations of paternal origin and probability increasing with paternal age (anticipation)
- Cellular and molecular mechanisms of the achondroplasia phenotype involve FGF3R overactive signaling inhibiting chondrocyte proliferation and hypertrophy resulting in reduced endochondral bone formation
- Treatment for achondroplasia includes environmental adaptations to stature early during development, growth hormone treatment, limb extension, and various pathway inhibitors.
Test your knowledge on autosomal dominant and recessive inheritance patterns, monogenic and polygenic diseases, and the genetic and clinical aspects of achondroplasia. This quiz covers Mendelian genetics, gene dosage effects, variant gene products, inheritance frequencies, and the molecular mechanisms and treatment options for achondroplasia.
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