Weeks 5+6 Flashcards
Linkage
When genes don’t assort independently, genes are located on the same chromosome, more likely the closer the genes are
Why do recombinants occur?
Crossing over in meiosis I, the further apart the genes are, the more likely a crossover is to occur
What is Chi Squared Analysis used for?
To determine if numbers in categories are actually different and not due to chance - is it statistically significant?
Statistical significance
Results are not able to be explained by chance, null hypothesis is rejected, P value less than 0.05
Steps for doing Chi Squared Analysis
- Identify parental and recombinants
- Identify what expected values are for P and R
- Sum of categories [(observed - expected)^2/expected]
- Determine degrees of freedom (#categories -1)
- Chi squared table to find P value
Two point crosses
Determine relative gene positions
- difficult to determine order when genes are close together
- actual distances don’t always add up for far apart genes
Three point crosses
Uses three marker genes, more accurate, accounts for double crossover correction
Steps of doing a three point cross:
- Determine parental and recombinant classes
- Compare parental and double crossovers to determine the middle gene
- Determine distance between middle gene and adjacent (add recombinants, divide by total, multiply by 100)
- Determine distance between far genes by adding recombinants + double X (x2), divide by total, multiply by 100
dNTP
Made up of phosphate, deoxyribose, nitrogenous base (either pyrimidine or purine)
How do nucleotides connect?
Phosphodiester bonds between 3’ carbon and phosphate group of previous base
Direction of DNA strands
Antiparallel
- phosphate is 5’
- OH end is 3’
Complementary base pairing
A pairs to T (two H bonds)
G pairs to C (three H bonds)
How was DNA determined to be the unit of inheritance?
(1944) Avery, MacLeod, McCarty added enzymes that broke down either protein or nucleic acids to bacteria to see which caused lethal bacteria to still form (using transformation)
Chase and Hershey
In 1952 they infected bacteria with bacteriophages that contained tagged DNA or tagged proteins, and saw which was found inside bacteria
DNA structure
- Helix due to X-ray diffraction
- Equal amounts of A and T, G and C
- Major and Minor grooves
Eukaryote genome structure
Linear, double stranded chromosomes
Prokaryotes genome structure
Circular, double stranded chromosomes
Virus genome structure
Single stranded DNA
Retroviruses genome structure
RNA genome
Viruses
Not alive, no cells, made of DNA and proteins, requires host cell to replicate
DNA Replication
Occurs in S phase of cell cycle, semiconservative
Mechanism of DNA replication
Initiator recognizes origin of replication (which is an AT rich site), helicase unwinds DNA, topoisomerase relieves pressure
- RNA primer added, DNA Pol III adds bases to 3’ OH on primer
- DNA Pol I removes primers and fills in gap with DNA
- DNA ligase Attaches 3’OH and 5’PO4 ends of Okazaki fragments
Telomeres
Non coding repeats at the ends of chromosomes, designed to protect DNA from degrading due to replication
Telomerase
Has RNA compliment with overhang, allows DNA Pol III to bind and replicate
- Most somatic cells in humans don’t have it
