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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 size, shape, and genetic content
Terminology
• Somatic cell- any cell other than a sperm or egg cell
– Cells that make up your body: cheek, blood, brain, bone, liver, kidney
• Diploid (2n) cell
– contains two sets of chromosomes
– one set comes from the mother, the other from the father
• 46 chromosomes in human somatic cells (23 pairs)
Terminology • Gamete- reproductive cell
– sperm or egg cell
– A human gamete contains 23 chromosomes
• Haploid (n) cell
‒ contains only one set of chromosomes
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 n
Egg + 23 chromosomes + n
Total 46 chromosomes 2n (diploid)
Sometimes chromosomes replicate incorrectly during Synthesis phase of mitosis (DNA replication)…
Chromosomal Mutations
Chromosomal Mutations
• Mutations- changes in an organisms chromosome structure
–Deletions
–Duplication
–Inversion
–Translocation
Chromosomal Mutations
Original Chromosome:
Deletion- when a piece of chromosome breaks off completely
Duplication- a chromosome fragment attaches to its homologous chromosome
1 2 3 4
1 2 4
1 2 3 4 1 2
Chromosomal Mutations
• Inversion- when the chromosome piece reattaches to the original chromosome but in a reverse orientation
• Translocation- when the chromosome piece reattaches to a nonhomologous chromosome
1 2 3 4
1 2 3 4 9
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 size, shape, and structure of each chromosome
Karyotypes
• Humans have 23 pairs of chromosomes (46 total)
• Sex chromosomes- the last pair (#23)
– Determine the gender of an individual
• Females (XX)
• Males (Xy)
• Autosomes- are all chromosomes other than sex chromosomes (pairs 1-22)
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 chromosomes fail to separate correctly during mitosis (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:
–Missing 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