chromosomes and karyotypes what is a chromosome terminology chromosomal mutations differences among...
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Chromosomes and Karyotypes
What is a ChromosomeTerminology
Chromosomal MutationsDifferences among species
KaryotypesNondisjunction 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
TerminologyHaploid (n)Diploid (2n)
n = 23Sperm 23 chromosomes nEgg + 23 chromosomes + nTotal 46 chromosomes 2n
(diploid)
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 41 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 34
1 2 349
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
NondisjunctionCommon 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
NondisjunctionCommon 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
NondisjunctionCommon 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