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 n Egg + 23 chromosomes + n Total 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

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

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