chapter 5 Flashcards
Thomas Hunt Morgan’s work on Drosophila (fruit flies) established what?
the chromosome theory of inheritance, genetic linkage, and recombination.
What are synthetic genes?
Genes located on the same chromosome
What are linked genes?
Syntenic genes that are close enough to each other that their alleles do not independently assort.
When does recombination occur during meiosis?
when crossing over reshuffles alleles between homologous chromosomes
If crossing over does not occur between linked genes, the genes are said to exhibit what?
complete gene linkage
What is Incomplete genetic linkage?
When there is a mix of parental and recombinant gametes, with recombination frequencies varying depending on the distance between genes on the chromosome
Do linked genes assort independently?
No, meaning there will be a higher frequency of parental allele combinations compared to nonparental combinations
What is recombination frequency?
The frequency at which recombination occurs between genes; this frequency is used to estimate the distance between genes on a chromosome
What did Bateson and Punnett discover?
They discovered evidence of genetic linkage in their sweet pea experiments, and Morgan’s work with Drosophila provided further evidence.
What was the cytological evidence?
Work by Creighton and McClintock (in corn) and Curt Stern (in fruit flies) showed that genetic recombination corresponds to physical exchange between chromosomes, providing direct evidence of the crossover process
What are recombinant chromosomes?
Alleles of syntenic genes can be reshuffled when crossing over occurs between homologs
What are nonrecombinant chromosomes?
Homologs that do not reshuffle alleles under study
What is genetic linkage mapping?
plots the positions of genes on
chromosomes
What did Morgan study?
the white (eye color) and miniature (wing
size) genes
What is a two-point test cross?
Morgan realized that linkage of autosomal genes in Drosophila could be interpreted
What is genetic linkage?
When genes are located close to each other on the same chromosome, they tend to be inherited together
The closer genes are together the _______ recombination frequency
lower
Who created the first genetic linkage map?
Alfred Sturtevant, working with Thomas Morgan by analyzing recombination frequencies in Drosophila
What are map units?
Recombination frequencies are used to calculate genetic distances, measured in map unit. 1% = 1 cM (centiMorgan)
What factors influence hot spots?
species, age, sex, and environmental factors
What is the chi-squared analysis?
Statistical methods like chi-square tests are used to confirm whether the observed genetic linkage is significantly different from independent assortment.
What are hotspots?
They influence the apparent distance between genes in genetic maps.
What are challenges with gene mapping?
Human genes are more challenging to map due to limitations in controlled mating and sample size
What are Genome-Wide Association Studies (GWAS)?
They use SNPs to locate genes associated with traits and diseases across the genome. they are then plotted using manhattan plots
What is linkage disequilibrium?
When alleles of genes are inherited together more often than expected by chance
What are genetic markers?
Different variants of DNA sequence constitute the genetic markers used to study locations of genes
What are the genetic markers?
variable number tandem repeats (VNTRs), single nucleotide polymorphisms (SNPs), and restriction fragment length polymorphisms (RFLPs)
What are restriction fragments?
Pieces of DNA resulting from restriction enzyme cutting
What are restriction enzymes?
RFLPs are changes in DNA sequence that are detected using DNA-cutting enzymes
What is a haplotype?
The specific array of SNPs in a small region on a single chromosome
What is the allelic phase?
The arrangement of alleles of linked genes on parental chromosomes
The logarithm of the odds ratio gives what?
The lod score
What is the theta value?
Lod score determines the likelihood of linkage for many recombinant frequencies
The highest lod score value is what?
Zmax
A theta value of 0 means what?
complete linkage
A theta value of 0.5 means what?
independent assortment
GWAs look for what?
Associations between traits and groups of alleles in populations
A lod score of 3.0 or higher is…
considered significant evidence in favor of linkage at the theta value
Lod scores of less than −2.0…
represent significant evidence against genetic linkage
Lod scores between these two values are…
inconclusive regarding linkage
What is linkage equilibrium?
The genotype for a chromosome at one gene is expected to be independent of its genotypes for other genes
The CARD15 gene was suggested to be
associated with what disease?
Crohn’s Disease (C D) based on GWAS
results
What are Mendelian Conditions?
Caused by a single gene mutation, following inheritance patterns like autosomal dominant, autosomal recessive, and X-linked
What are chromosomal conditions?
Result from changes in chromosome number or structure, such as trisomy 21 (Down syndrome)
What are Multifactorial Conditions?
Involve both genetic factors and environmental influences (e.g., diabetes).
What are the types of genetic testing?
molecular analysis, biochemical analysis, and chromosome analysis. They help diagnose genetic conditions, detect carriers, and assess the risk for future offspring.
What do carrier testing and presymptomatic testing allow?
allow individuals to understand their genetic risks and make informed decisions, especially for diseases like Huntington’s.
What are consultands?
Individuals working with genetic counselors
What is the Bayesian analysis?
determines the probability of a certain genotype occurring in a certain family member
What is presymptomatic testing?
used for genetic conditions that have a late age of onset
What is newborn testing?
set of mandated genetic tests that together require only a few drops of blood
What is prenatal testing?
testing performed during pregnancy for the purpose of determining whether a fetus has a particular condition or disorder.
know the indicators and goals for genetic counseling
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