Chromosomes and ploidy Flashcards
How is DNA organized when it is not in chromosomes?
DNA is a double-stranded molecule that is enrolled around protein complexes called histones. This compound is called a nucleosome. Nucleosomes are linked by segments of DNA called DNA linker.
What happens when chromosomes condense?
The nucleosomes come very close to each other and compact. They compact in chromatin fibers, so they are made of DNA and proteins. This way, chromosomes are highly organized parts of chromatin. They need to have every gene touching out for the enzymes to reach them.
Why does DNA have to condense before and during cell division?
One DNA molecule can be up to 2m long. A cell is much smaller… Furthermore, it makes it easier for chromosomes to be condensed when division occurs and it avoids the loss of some parts of chromosomes, which could have implications on the daughter cells that would not be identical.
What letters are associated with each arm of a chromsome?
Long arm = q Short arm = p
How many telomeres are there in each chromosomes?
There is one at the end of each arm of a chromosome. SS have 2. DS have 4.
What is the best way of counting chromosomes?
Count the centromeres. One centromere = One chromosome
How many chromatids are there in a single-stranded chromosome?
Zero. Only ds chromosomes have chromatids.
How many molecules of DNA is there in a DNA double helix?
Each DNA double helix is one molecule of DNA?
What is the distinction between single and double-stranded chromosomes?
Ss chromosomes are the ones before DNA replication in the S-phase of the interphase, before mitosis. Ds chromosomes, on the other hand, are made up of two identical DNA molecules instead of one. They occur after DNA replication and are composed of chromatids held together at the centromere. A ds chromosome has 2 chromatids.
What determines the number of sets of chromosomes that a cell has?
The ploidy level
What is the ploidy level of n, 2n, 3n,4n and 6n?
Haploid, Diploid, Tetraploid and Hexaploid
What is a set of chromosomes?
It is a group of chromosomes that are different. None of the chromosomes in one set has an homologous chromosome.
How do we call chromosomes of the same type, that code for the same genes?
Homologous chromosomes
What do homologous chromosomes have in common?
They are of the same size, same shape, they have the same genes (but maybe different alleles) in same locus.
Are homologous chromosomes identical?
NO. They may have different alleles.
