IMED1002 Study Guide - Midterm Guide: Phosphodiester Bond, Prokaryote, Nucleosome
LECTURE 13 – CHROMOSOMES
Chromosomes exist as pairs in the nucleus of our cells. A single copy of the pair is called a
chromatid/genome and is made up of a molecule of double-stranded DNA where the functional
regions of this DNA are called genes. Chromosomes have two main roles: faithful transmission and
appropriate expression of genetic information. We use n to describe the no. of different
chromosomes and C to describe the DNA content in picograms – for example, human cells have n=
23 and C= 3.5pg.
Define:
Ploidy – number of copies they have in chromosome set
Haploid – n chromosomes = 23 chromosomes (DNA content of C)
Diploid – 2n chromosomes = 46 chromosomes (DNA content of 2C)
Polyploid – 4n = 92 chromosomes (anything more than 2n)
Karyotype – chromosome number, size and shape at metaphase are species-specific
What is a homologous pair and what is a single copy of that pair called? Why do humans have
homologous pairs?
Homologous pairs are when a diploid organism has 2 sets of chromatids/genome, they are alike in
structure, size, carry same genetic information. A single copy is called an chromatid/genome.
Humans have homologous pairs because of sexual reproduction where one set is from male parent
and one from the female parent.
Define/describe the differences between somatic and germ line cells
Somatic cells are cells outside the germ line and are usually diploid. Germ line contains a subset of
diploid body cells that give rise to gametes (egg/sperm), which are haploid cells (gametes).
Which phase of replication can we see chromosomes?
Metaphase phase
Describe the three elements needed for chromosomes to be copied
1. Centromere – narrowest part of chromosome
2. Replication origins – sequence needed to initiate DNA replication
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Document Summary
Chromosomes exist as pairs in the nucleus of our cells. A single copy of the pair is called a chromatid/genome and is made up of a molecule of double-stranded dna where the functional regions of this dna are called genes. Chromosomes have two main roles: faithful transmission and appropriate expression of genetic information. We use n to describe the no. of different chromosomes and c to describe the dna content in picograms for example, human cells have n= Ploidy number of copies they have in chromosome set. Haploid n chromosomes = 23 chromosomes (dna content of c) Diploid 2n chromosomes = 46 chromosomes (dna content of 2c) Polyploid 4n = 92 chromosomes (anything more than 2n) Karyotype chromosome number, size and shape at metaphase are species-specific. Homologous pairs are when a diploid organism has 2 sets of chromatids/genome, they are alike in structure, size, carry same genetic information.
