Chapter 3.2 Chromosomes Flashcards
Diploid nuclei
a nucleus that has chromosomes organized into pairs of homologous chromosomes. Most cells in the human body are diploid, and in each cell the nucleus contains a set of 23 chromosomes from the mother and 23 from the father.
Haploid nuclei
have one chromosome of each pair. (male bee, wasp and ant cells are haploid)
karyogram
shows the chromosomes of an organism in homologous pairs of decreasing length. Shape depends mainly on the position of the centromere.
Sex is determined by?
Sex chromosomes
Autosomes
chromosomes that do not determine sex
Homologous chromosomes
similar in shape and size, carry the same sequence of genes but not necessarily the same alleles of those genes
Why do prokaryotes have 1 single chromosome while others have a pair
they can reproduce using binary fission
Some prokaryotes have plasmids but eukaryotes do not
have small loops of DNA that are extra copies of some of the genetic material of the organism. These loops are called plasmids. These small circular DNA molecules are not connected to the main bacterial chromosome. They replicate independently of the chromosomal DNA.
Nucleosome
consists of two molecules of each of four different histones
Characteristics of prokaryote chromosomes
only 1, circular shape, no histones, sometimes presence of plasmids, not organized into pairs
Characteristics of eukaryote chromosomes
2 or more, linear shape, histones present, never plasmids, is organized into pairs
Gametes
Sex chromosomes, only contain 23 chromosomes in total. they are said to be haploid.
Chromosome number of humans
46 (23 pairs)
Karyotype
the specific number and appearance of the chromosomes in his or her cells
How is a karyogram made
- cells are stained and prepared on a glass slide, to see their chromosomes under a light microscope
- photomicrograph images are obtained of the chromosomes during a specific phase of cell division called the mitotic metaphase
- images are cut out and separated, a process that can be done using scissors or a computer
- images of each pair of chromosomes are placed in order by size and the position of the centromere.
Sex chromosomes
23rd pair, determine whether a person is male or female. the X chromosome is longer than the Y chromosome, and contains many more genes. In human females there are 2 X chromosomes, when they produce gametes, each egg will contain 1 X chromosome. Males have one X and one Y. When males produce sperm cells, 1/2 of them contain X and 1/2 contain Y –> 50% chance girl or boy
Autoradiography
a technique in which radiation from a substance is captured on photographic film or by a camera sensor. Used to obtain images of DNA strands so that their lengths can be measured.
Cairns’ technique for autoradiography
involves injecting radioactive materials into the DNA samples that will expose the film faster. In the case of measuring the lengths of DNA strands, the DNA forming during replication is given a radioactive form of a molecule called thymidine. Thymidine is a component of a DNA nucleotide made up of a pentose sugar bonded to thymine. The radioactive form added in the experiment is called 3H-thymidine, in which the 3H is the radioactive isotope of hydrogen. it is used as a radio maker to keep track of where those thymidine molecules are. This technique was used by John Cairns in 1962 to demonstrate that a bacterium’s chromosome is made up of a single strand of DNA and that it is replicated by being unzipped.
isotope
a version of an atom with a different atomic mass compared with other versions of the same atom, usually because it has more neutrons
