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