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