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.
Who discovered how transformation actually works?
Avery, Macleod, and McCarty, discovered that DNase was preventing the bacteria from transforming their genetic information.
What is T2
A bacteriophage
Describe the life cycle of a bacteriophage
- Phage attaches to a cell and injects its chromosome into the host
- The host chromosome is broken apart and integrated into the host chromosome
- More phages are produced, host cell is lysed and killed.
Hershey Chase Experiment 1952?
Discovered that DNA is the genetic material in phages.
Heinz Fraenkel-Conrat and Singer demonstrated?
That RNA carries the genetic material in TMV (Tobacco Mosaic Virus)
Who started studying DNA structure via diffraction?
William Ashbury 1947
Primary DNA structure
String of nucleotides joined together by phosphodiester linkages
Secondary DNA structure
Three dimensional structure that was discovered by Watson and Crick
Tertiary Structure
The complex packaging of double helix into chromosomes
Three different forms of DNA?
- A form
- B form
- Z form
How is the primary structure in DNA modified?
Through methylation
How does DNA condense in tertiary form?
By supercoiling
Differentiate histone, nucleosome, and chromatin
- Histone is the protein DNA is wrapped around
- Nucleosome is made up of eight histones wrapped together via DNA
- Chromatin is the description of the “string and beads” that form tertiary structure.
What is histone H1?
Acts like a clamp to stabilize DNA around the nucleosome core.
30-nm Chromatin
Adjacent nucleosomes packing together
Types of chromatin
Euchromatin -> Less condensed, found on chromosomes, contains most genes, often transcribed.
Heterochromatin -> More condensed, found at centromeres, and telomeres, mostly made of repeated sequences, contains few genes, crossing over is uncommon.
Chromosomal puff
Indicator of where transcription is actively happening
Histone tails and their involvement in transcription
When they are positively charged they are tightly bound to the DNA inhibiting transcription factors. Acetylation weakens the interaction causing the DNA to be more accessible.
Centromeres
Constricted region to which spindle fibers attach during mitosis and meiosis.
Telomeres
Sequences at the end of chromosomes, highly repeated sequences that interact with proteins.
What are required to make Artificial Chromosomes in eukaryotes
- Telomeric sequences specific to the organism
- Centromeric sequences specific to the organism
- One or more origins of replication
Transposable elements
- Ubiquitous among forms of life
- Comprise of a high percentage of the genome
Two major classes of transposons
-Dna only
-Retrotransposons (uses RNA intermediate)
What ways can transposons drive chromosomal rearrangement?
Deletion
Duplication
Inversion
Transposable element can cause flanking direct repeats?
True
Transformation
Uptake of DNA from the environment
Transduction
Phage mediated transfer of DNA
Conjugation
Transfer via cell to cell contact
The F factor
Integrated in a bacterial chromosome in an HFr cell
R plasmid
Conjugative plasmids that carry antibiotic resistance genes
Bacteriophages can have two alternative life cylces
Lytic
Lysogenic
Primary Down Syndrome
Three copies of chromosome 21
Familial Down Syndrome
Translocated chromosome from 21 to 15
Specialized transduction
Is specific to a certain sequence of the chromosome
Types of Inversion
Paracentric -> Specific to a certain spot
Pericentric -> Include the centromere
F+
Present as separate circular DNA
F-
Absent
Hfr
Present, integrated into the bacterial chromosome
F’
Present as a separate circular DNA, carrying some bacterial genes
