WEEK 4 Flashcards
How are recombinant (different) phenotypes formed?
Crossing over in meiosis
What is the difference between recombinant phenotypes and non-recombinant phenotypes?
Recombinant phenotypes are different from their parents due to crossing over and non-recombinant phenotypes are identical to their parents
What is ‘Crossing over’?
During Meiosis paired chromosomes from each parent align so that similar DNA sequences from the paired chromosomes cross over one another and swap genetic material.
What do double exchanges of genetic material result from?
Double crossovers (DCOs)
It is possible that in a single tetrad, two, three or more exchanges will occur between nonsister chromatids as a result of several __________________ events
crossing over
What criteria must be met to execute a successful mapping cross?
- The genotype of the organism producing the crossover gametes must be heterozygous at all loci under consideration (If homozygosity occurred at any locus, all gametes produced would contain the same allele)
- The cross must be constructed so that the genotypes of all gametes can be accurately determined by observing the phenotypes of the resulting offspring
- A sufficient number of offspring must be produced in the mapping experiment to recover a representative sample of all crossover classes.
Why must the mapping cross be constructed so that phenotypes can be observed in the resulting offspring?
Because gametes and their genotypes can never be observed directly
What are the three different arrangements of genes in determining the gene sequence?
- (I) w-y-ec (y is in the middle)
- (II) y-ec-w (ec is in the middle)
- (III) y-w-ec (w is in the middle)
What is the method for determining the gene sequence? (method 1)
First, determine the arrangement of alleles on the homologs of the heterozygote yielding the crossover gametes by identifying the reciprocal noncrossover phenotypes. Then, test each of the three possible orders to determine which one yields the observed doublecrossover phenotypes—the one that does so represents the correct order
What is the method for determining the gene sequence? (method 2)
Following a double-crossover event, the allele in the middle position will fall between the outside, or flanking, alleles that were present on the opposite parental homolog.
determine the arrangement of alleles on the homologs of the heterozygote yielding crossover gametes. Then examine the actual double-crossover phenotypes and identify the single allele that has been switched so that it is now no longer associated with its original neighboring alleles. That allele will be the one located between the other two in the sequence.
What are Restriction fragment length polymorphisms (RFLMs)?
polymorphic sites generated when specific DNA sequences are recognized and cut by restriction enzymes.
What are ‘Microsatellites’ or ‘Short tandem repeats’?
Short repetitive sequences that are found throughout the genome, and they vary in the number of repeats at any given site
What are three types of DNA markers?
- Restriction fragment length polymorphisms (RFLPs)
- Microsatellites or Short tandem repeats
- Single-nucleotide polymorphisms
What is Cystic Fibrosis and what is it an example of?
Cystic fibrosis is an example of a gene located using DNA markers
It is a life-shortening autosomal recessive disorder resulting in excessive, thick mucus that interferes with the function of organs (e.g lungs and pancreas). Faulty gene is found on the long (q) arm of chromosome 7.
What were the 7 common human diseases associated between 24 genomic locations using SNPs and DNA markers?
- Type 1 Diabetes
- Type 2 Diabetes
- Crohn’s disease
- Hypertension
- Coronary artery disease
- Bipolar disorder
- Rheumatoid arthritis
