Chromosomes,
Karyotypes
and genes
Mrs. Stewart
Honors Biology
Central Magnet School
Standards
• CLE 3210.4.2 – Describe the relationships
among genes, chromosomes, proteins, and
hereditary traits.
Objectives: (today, we will…)
• Build a karyotype
• Examine karyotypes to determine the
presence or absence of genetic disorders
• Analyze the gene that determines sex of
offspring
• Use the effects of crossing over to determine
gene linkage
Chromosome Structure
• Chromosome definition:
in a eukaryotic cell, one of the structures in the nucleus that
are made up of DNA and protein; in a prokaryotic cell, the
main ring of DNA
Chromosome Vocabulary
• Histones:
a type of protein found in the
chromosomes of eukaryotic cells but not
prokaryotic cells.
• Chromatid:
one of the two strands of a chromosome that
become visible during meiosis or mitosis
• Centromere:
The region of the chromosome that holds the
two sister chromotids together during mitosis
Chromosomes
• What do they look like?
They look like an “X” just before
the cell divides and an “I” after they
divide.
• How many do humans have?
23 Pairs of chromosomes (23 from mom, 23 from dad)
Chromosome or Chromatin?
• Chromosome:
Tightly coiled DNA & proteins during cell division;
DNA cannot be “read” while in this form.
• Chromatin:
Loosely coiled DNA & proteins during the
cell’s life other than cell division. DNA can be
“read” to direct activities of the cell.
With your partner:
• Do more complex organisms
have more chromosomes?
With your Partner:
• Does every cell have
46 chromosomes?
Cell Types:
based on chromosome number
• Diploid 2n: (adj)
Describes a cell with two copies of each type of
chromosome.
Example: Animal body cells.
• Haploid n: (adj)
Describes a cell with one set of chromosomes.
Example: sex cells (sperm & egg); all prokaryotes (bacteria)
• Visual clip from book:
What is it?
• Karyotype:
an array of the
chromosomes
found in an
individual’s cells at
metaphase of
mitosis and
arranged in
homologous pairs
and in order of
diminishing size
What can a karyotype tell us?
Determine sex
Diagnose some genetic disorders
•Extra chromosomes or pieces
•Missing chromosomes or pieces
Chromosomes
• Dark Bands:
Are unique to each type of
chromosome; they are genes.
Types of Chromosomes
• Sex Chromosomes:
In animals this pair of chromosomes
determine the gender of the animal
• Autosome:
Any chromosome that is not a sex chromosome.
• Homologues:
Homologous chromosomes that have the same sequence
of genes, that have the same structure, and that pair during
meiosis
How do chromosomes pair on
a karyotype?
With their homologue.
Karyotype activity
• http://learn.genetics.utah.edu/content/begin/tr
aits/karyotype/
What makes a boy become a
boy?
• Like other homologues, the sex
chromosomes pair during Meiosis I
• What are the chances of a sperm cell
receiving a “Y” chromosome?
50:50
• Sex determination
– Sex determining Region Y or “SRY”
– Protein that causes gonads of embryo to develop
as testes
Sex-Linked Genes and Traits
• Traits that are
coded for by an
allele on a sex
chromosome
Which gender displays
recessive sex-linked disorders
more often and why?
Meiosis Gone Wrong
• Nondisjunction – homologous
chromosomes fail to separate during
Meiosis.
• This results in a gamete that will carry too
many or too few chromosomes.
Gene Linkage
• Geneticists hypothesized that genes
inherited together, must occur on the same
chromosome.
– Fly body color
– Fly eye color
– Fly wing type
• Pairs of genes that tend to be inherited
together are called “linked”.
• Gene linkage visual concept
How do we know where the
genes are on a chromosome,
in relation to each other?
• Gene loci (locations)
can be determined
based on crossingover frequencies
• The cross-over
percentage determines
the number of “map
units” apart
Chromosome Mapping
• A chromosome map is a diagram that
shows the linear order of genes on a
chromosome.
• Map unit – one percent frequency of crossover unit
• Crossing over visual concept
• Chromosome map visual concept
Exit Ticket
• m.socrative.com
• Room: stewart348