Genetics Exam 2 Flashcards
How do genes far apart segregate?
Independently
How do genes that are linked segregate?
With a frequency dependent on the distance from each other
A two-strand double crossover between two linked genes produces?
Non-recombinant gametes
Three types of crossovers can occur over three linked loci.
Single -> A and B: Swap of B and C
Single -> B and C: Swap of C
Double -> Swap of B
Study
Slide 19 Lecture 6
Three methods of mapping genes on chromosomes
Deletion mapping
Somatic cell hybridization
In situ hybridization
Deletion mapping
A part of the chromosome is deleted and a homozygous cross occurs. If the chromosome displays the recessive gene you know the gene of interest is in the deletion region.
Somatic-cell hybridization
Somatic cell hybridization is when two organisms cells are fused together and the hybrid cells are analyzed for certain gene products.
In situ hybridization
Attaches probes on sequences to be analyzed. For example fluorescence.
Aneuploidy
One set of chromosomes could have more than 2. For example 2n + 1 = 7
Polyploidy
All sets of chromosomes have more than 2. For example 3n = 9
Duplication
Genes are duplicated -> Looping out is a characteristic in heterozygotes
Can cause unbalanced gene dosage which leads to abnormalities.
Deletion
Removal of genes -> Looping out is a characteristic in heterozygotes
Pseudodominance can occur because recessive alleles are expressed
Haploinsufficient can occur when the deleted copy results in a low gene dosage that has a small effect on the wild-type phenomenon.
Inversion
Inverts the sequence of the gene on a chromosome -> They can interrupt individual genes, destroying expression. Genes moved around may experience different expressions due to positional effects. Heterozygous inversions lead to decreased crossing over in the inverted region. When crossed over it can cause non-viable gametes.
Translocation
Swaps gene sequences from chromosomes -> Has the same effects as inversion
Robertson Translocation
A translocation that combines two giant chunks of chromosomes. An example is chromosome 2 on a human.
Three types of segregation
- Alternate -> Viable
- Adjacent 1 -> Non-viable
- Adjacent 2 -> Non-viable
Fragile sites
Chromosomal regions that are susceptible to breakage under certain conditions.
Causes of Aneuploidy
-Loss of centromere
-Small chromosomes -> Robertson Translocation
-Non disjunction either in Meiosis I or II
-Non disjunction in Mitosis
Types of Aneuploidy
Nullisomy - Loss of both chromosomes of a pair
Monosomy - Loss of one chromosome
Trisomy - Gain of an extra chromosome
Tetrasomy - Gain of two extra homologous chromosomes
Aneuploidy in Humans
Usually lethal, but can lead to individuals with down syndrome
Causes of polyploidy
-Non disjunction either in Meiosis I or II
-Non disjunction in Mitosis
Who discovered DNA was a polymer of nucleotides
Phoebus Aaron Levene
Who discovered nitrogenous bases were associated with DNA
Albrecht Kossel
Who disproved tetra-nucleotide theory
Erwin Chargaff 1948
Who first demonstrated bacteria transformation?
Fred Griffith -> 1928, however could not explain it.