Chromosomes and Karyotypes
What is a Chromosome
Terminology
Chromosomal Mutations
Differences among species
Karyotypes
Nondisjunction disorders
What is a chromosome?
• Chromosome- coils of DNA and proteins
• Chromatid- two exact copies of DNA that
make up a chromosome
• Centromere- where the two chromatids
attach
Chromosome
Terminology
• Gene- segment of DNA that codes for a
protein or RNA molecule
– Units of information
Terminology
• Homologous chromosomes- are
chromosomes that are similar in shape,
size and genetic content
Terminology
• Somatic cell- any cell other than a sperm or egg
cell
– Cheek, blood, brain, bone, liver, kidney
• 46 chromosomes in human somatic cells
– 23 pairs
– One set comes from the mother, the other from the
father
• A diploid (2n) cell contains two sets of
chromosomes, like the somatic cell
Terminology
• Gamete- sperm or egg cell
– Carries one set of chromosome (has 23
total chromosomes)
• A haploid (n) cell contains only one set
of chromosomes, like the gamete cell
Terminology
• Fertilization- fusion of two gametes (fusion
of sperm and egg)
• Zygote- fertilized egg cell
– The first cell of a new individual
Terminology
Haploid (n)
Diploid (2n)
n = 23
Sperm 23 chromosomes
Egg + 23 chromosomes
Total 46 chromosomes
n
+n
2n
(diploid)
Chromosomal Mutations
• Mutations- changes in an organisms
chromosome structure
– Deletions
– Duplication
– Inversion
– Translocation
Chromosomal Mutations
Original Chromosome:
1
2
3
4
Deletion- when a piece of chromosome
breaks off completely
1
2
Duplication- a chromosome fragment
attaches to its homologous
chromosome
1
2
1
2
3
4
4
Chromosomal Mutations
• Inversion- when the chromosome piece
reattaches to the original chromosome
but in a reverse orientation
1
2
4
• Translocation- when the chromosome
piece reattaches to a nonhomologous
chromosome
1 2
9
4
3
3
Chromosomal Mutations
Differences among species
• Each organism has a characteristic
number of chromosomes
• The number is constant with the
species
• Potatoes, plums, and chimpanzees all
have 48 chromosomes
Differences among species
• Oats, Raccoon Dogs, Rats, Wheat and
Wolverines all have 42 chromosomes
Karyotypes
• A karyotype is
a picture of an
organisms
chromosomes
• It allows us to
study the
difference of
shape,
structure and
size of each
chromosome
Karyotypes
• Humans have 23 pairs of chromosomes
• Sex chromosomes- the last pair (#23)
on a karyotype that determine the sex
of an individual
– Females (XX)
– Males (Xy)
• Autosomes- are all other chromosomes
Karyotypes
• During mitosis, a picture is
taken
• The chromosomes are sorted
into identical pairs and
arranged from biggest to
smallest
• The 2 sex chromosomes are
put at the end (pair 23)
Nondisjunction
• Sometimes during meiosis, the
chromosomes fail to separate correctly
(called nondisjunction)
– Monosomy- when gamete has only 1 copy of
the affected chromosome
– Trisomy- when the other gamete has 3 copies
of one chromosome
Nondisjunction
Common Disorders
• Klinefelter’s syndrome:
– One to several extra sex chromosomes
• Ex. XXY or XXXY
• Turner’s syndrome:
– Only one sex chromosome
– Absense of Y develops into female
• Ex. XO
Nondisjunction
Common Disorders
• Down’s Syndrome:
– Autosomal
– Trisomy 21
– Most common birth defect
• Patau Syndrome:
–
–
–
–
Autosomal
Trisomy 13
Rarely live past infancy
Neurological problems, polydactyl and facial defects
Nondisjunction
Common Disorders
• Edwards Syndrome:
–
–
–
–
Autosomal
Trisomy 18
30% of babies die by 1 month
Learning disabilities, congenital heart defects and
malformations of digestive tract, urinary tract and
genitals