What is John cairns technique for measuring the length of DNA molecules by autoradiography?
1) cells were grown for 2 generations in culture medium containing tritiated thymidine
2) cells were then placed onto a dialysis membrane and cell walls were digested by enzyme lysosome - cells burst to release DNA
3) thin film of photographic emulsion was applied to surface of the membrane
4) end of two month period film was developed and examined
- images could be measured
What type of proteins do eukaryotes chromosomes have
Linear DNA associated with histone proteins
In eukaryote species what chromosomes are there?
Different chromosomes that carry different genes
What are homologous chromosomes?
They have the same sequence of genes but not necessarily the same alleles for those genes
What do haploid nuclei have?
One chromosome of each pair - contain 23 chromosomes
ex: gametes have haploid nuclei- each egg and sperm cell have 23 chromosome
What do diploid nuclei have?
Have pairs of homologous chromosomes - has two chromosomes of each type- contain 46 chromosomes
What does the number of chromosomes feature? And what does this mean?
It is a characteristic feature of members of a species - organisms with a different number of chromosomes are unlikely to be able to breed
How is sex determined
By sex chromosomes
What chromosomes do not determine sex (all other chromosomes) ?
What are the 2 chromosomes that determine sex?
What sex chromosome must all humans have and why?
All humans have at least one X chromosome as it had many genes which are essential in both males and females
Which chromosome determines whether it is a boy or girl and why?
Y chromosome is found in guys and one gene in causes fetus to develop into a boy- SRY or TDF
What chromosomes do sons/ daughters receive
Female: X from mother X from father
Male: X from mother y from father
What do karyograms show??
Shows the chromosomes of an organism in homologous pairs of decreasing length
When are chromosomes visible?
In mitosis, with cells in metaphase
How can kayeograms show if a child is downs?
3 copies of chromosome 21 - trisomy 21
What chromosomes do prokaryotes have?
Have one chromosome consisting of circular DNA molecule containing all the genes needed for the basic life processes of the cell- called naked