11) Theodor Bovril's Work on chromosome theory Flashcards
What is physical mapping?
Where the genes are actually located in the cell
What does ‘n’ and ‘C’ refer to in mitosis?
n= GENETIC content of cell 1n= Number of alleles for a gene locus in haploid cell
C= DNA content of a cell 1c= Amount of DNA cell present in a haploid cell
What are the 4 stages of mitosis?
Mitosis= Chromosomes in the nucleus divide when the cell does
1) G1= First gap, where cell is at rest so it is normal diploid cell, 2C and 2n
2) S phase= Synthesis: Signals e.g. growth hormones and environmental stress= Tells cell that its time to divide
First step: DNA Replication= Genome stays relatively open during this, can’t actually ‘see’ chromosomes. Lasts couple of hours in eukaryotes, minutes in prokaryotes
DNA doubles= 4C but amount of information stays same, 2n
3) G2= Second gap: Cell takes break
4c 2n= Various checks done after replication
4) M phase= Mitosis, split into 4 different events
Cell equally divides its contents inc genetic material between 2 daughter cells
1) Prophase: Chromosomes condense= Tighten up, VISIBLE chromosomes= Each chromosome consists of 2 copies (sister chromatids) held together at centromere + nuclear envelope breaks down (membrane surrounding nucleus)
2) Metaphase: All of chromosomes line up in middle of nucleus along equatorial
3) Anaphase: Building up= Each chromosome is pulled apart into its 2 chromatids= One chromatid goes into one daughter cell and the other goes into the other daughter cell. Chromatids= Pulled apart by single that attaches to centromere, one goes to north, other goes to south
4) Telophase: Nuclear envelope forms sound each of the 2 daughter nuclei and daughter chromosomes relax and decondense
What did Boveri show?
If you did not have correct assortment of chromosomes, the daughter cells will die
Looked at patterns of chromosome inheritance in polyspermic sea urchin embryos= Multiple sperm fertilise one egg
Result: Zygote has wrong number of chromosomes= Wrong number goes into daughter cells= No chromosomes and die
Showed: Genes are on chromosomes
What is chromatin? What is chromatid?
Chomatin= When the DNA strand is wrapped around histones, and can either be tightly wrapped or loosely= Normally loose in a cell
Chromatid= When one chromome gets duplicated (mitosis) so that now both pairs come from either dad OR mum (but not both) and one of the strands is called chromatid
Each sister chromatid= Double helix
Chromosomes are only visible when condensed (doing M phase)
What is a homologous pair?
Chromosomes exist in homologous pairs= Each of (diploid) cell carries 2 complete copies of genome= One from mother, one from father and each are split into chromosomes
Homologous pairs= Code for same thing but contains different alleles as one is from mother, one is from father= Each will have same basic structure
Gene loci are same order for each member of a pair, but alleles at a given gene locus do not have to be the same
