3.2 Chromosomes

define: gene mutation

change in base sequence of a gene

define: base substitution mutation

when one base is replaced by another base

Explain the difference between prokaryotic and eukaryotic chromosomes.

* prokaryotic chromosomes are found freely in the cytoplasm while eukaryotic chromosomes are contained within a nucleus


* prokaryotic chromosomes are naked while eukaryotic chromosomes are bound to histone proteins
* prokaryotic chromosomes contain plasmids while eukaryotic do not contain plasmids
* prokaryotic chromosomes are circular, eukaryotic chromosomes are linear

Def: Eukaryotic Chromosomes

long strands of DNA and associated proteins

Where are Eukaryotic Chromosomes found?

nucleus of eukaryotic cells

define: diploid

cell/nucleus with pairs of homologous chromosomes

define: haploid

cell/nucleus with only one chromosome of each pair

define: homologous chromosomes

chromosomes that are similar in size/shape, same sequence of genes, not necessarily alleles of those genes

How does chromosomes affect sex?

* Females possess two copies of a large **X** chromosome (XX)
* Males possess one copy of an **X** chromosome and one copy of a much shorter **Y** chromosome (XY)

Def: autosomes

chromosomes that do not affect sex

Outline the process of karogyrams

Karyotypes are the number and types of chromosomes in a eukaryotic cell – they are determined via a process that involves:

* Harvesting cells (usually from a foetus or white blood cells of adults)
* Chemically inducing cell division, then arresting mitosis while the chromosomes are condensed
* The stage during which mitosis is halted will determine whether chromosomes appear with sister chromatids or not

If someone has down syndrome, what is affected?

three 21st chromosomes (trisomy 21)