unit 4: chromosome discovery & structure

Mendelian “factors”

Discovery of the Chromosome:

• carried traits from one generation to the next

Walther Flemming

Discovery of the Chromosome:

• recognized and explored the fibrous network within the nucleus: chromatin or "stainable material"

the precise distribution of nuclear material

Discovery of the Chromosome: Walther Flemming

• observed cells in various stages of division and recognized that chromosomal movement during mitosis offered a mechanism for ___ during cell division

Theodor Boveri

Discovery of the Chromosome:

• provided the first evidence that germ cell chromosomes imparted continuity between generations

• one of the pioneers of embryology

• looked at not only the nuclei but other changes

Ascaris embryos

Discovery of the Chromosome: Theodor Boveri

• provided one of the first descriptions of meiosis

Walter Sutton

Discovery of the Chromosome:

• confirmed and expanded upon Boveri's observations

• described the configurations of individual chromosomes in cells at various stages of meiosis (testes of Brachystola magna)

Chromosomal Theory of Inheritance

Discovery of the Chromosome: Sutton & Boveri

• provided the physical basis of the Mendelian law of heredity

1910, Thomas Hunt Morgan

Discovery of the Chromosome: Sex Chromosomes & Specific Genes

• Experimentally demonstrated Chromosomal Theory of Inheritance using Drosophila melanogaster

• pioneered “Fly Room” experiments

1916, Calvin Bridge

Discovery of the Chromosome: Sex Chromosomes & Specific Genes

• helped establish the chromosomal basis of heredity and sex

• non-disjunction/separation of chromosomes during meiosis

Aneuploidy

Discovery of the Chromosome: Sex Chromosomes & Specific Genes - Bridge

improper/abnormal number of a chromosome set

Chromosome

• Threadlike structures or “colored bodies”

• Factors that distinguish one species from another

Made of protein and a single molecule of DNA

Chromosome composition

histones

Chromosome:

protein component involved in the wrapping of the DNA molecule until it becomes a hyper-looped structure

Enable transmission of genetic information from one generation to the next

What do chromosomes do?

mitosis

What do chromosomes do?

Ensure daughter cell retains its own complete genetic complement

meiosis

What do chromosomes do?

Enable each mature ovum and sperm to contain a unique single set of parental genes

44

Human Chromosome:

autosomes

2

Human Chromosome:

sex chromosomes/gametes

Autosomal inheritance

Human Chromosome:

inheritance through the cell’s bodies

Modern way of staining chromosomes

Human Chromosome:

chromosomes are given different colors

euchromatin and heterochromatin

Human Chromosome:

banding patterns

Euchromatin

Human Chromosome:

genetically “transcriptionable” areas of the chromosome

chromosomes as hereditary vehicles

What do Chromosomes do?

facilitates reproduction and maintenance of species

Extra-chromosomal DNA

Human Chromosome:

Other DNA materials found in mitochondria

Metaphase Chromosome

Replicated condensed chromosome with sister chromatids

Telomere

Metaphase Chromosome:

• regions at the end of linear chromosomes

• look like aglets

• protect the chromosomes from being destroyed at the tips

• without this, there will be less information at the end regions

pairing of homologous chromosomes

Metaphase Chromosome: Telomere

• attach the cells at the side of nuclei that allows for ___

telomerase

Metaphase Chromosome: Telomere

• enzyme that makes sure information at the end of the chromosome is kept

Male karyotype at metaphase

147 nucleotide pairs of DNA

Metaphase Chromosome:

wrapped around the histone

H1

Metaphase Chromosome:

• serves as the closer of the DNA loop around histones

• octamer

• allows for the zigzag structure which creates a tighter structure

basic amino acids

Metaphase Chromosome:

Histone is rich in ___ which allows for positive charges to be present & attract phosphate

Nucleosomes

Metaphase Chromosome:

• “beads on a string”

• 3D zigzag structure

8 subunits of globus(?)/globular proteins

Nucleosomes:

a bead is composed of ___

anchoring proteins/scaffold

Metaphase Chromosome:

helper proteins

Radial loop domains

Metaphase Chromosome:

compaction of radial loops

Chromatids

Morphology of Chromosomes:

Two identical strands which are the result of DNA replication

Centromere

Morphology of Chromosomes:

• Central region

• Primary constriction where sister chromatids are linked

• Consists of several hundred kilobases of repetitive DNA

• Responsible for chromosome movement at cell division

p (petite)

Morphology of Chromosomes: Centromere

Short arm

q (queues or “g” = grande)

Morphology of Chromosomes: Centromere

Long arm

13 chromosomes

Morphology of Chromosomes: Centromere

we can actually see the long and short arm

Kinetochore

Morphology of Chromosomes:

• attaching point of microtubules

• Microtubule organizing center (MTOCs)

• Facilitates spindle formation

Monocentric

Chromosome Types: Number

• Single centromere

• Reliably transmitted from parental to daughter cells

Acentric

Chromosome Types: Number

• Lacks centromere

• genetically unstable because they cannot be maneuvered properly during cell division and are usually lost

Dicentric

Chromosome Types: Centromere Number

• Two centromeres

• genetically unstable because it is not transmitted in a predictable fashion

Metacentric

Chromosome Types: Centromere Position

• Middle; yielding arms of roughly equal length

• centrally located

• 5 pairs in humans

• v-shaped

Submetacentric

Chromosome Types: Centromere Position

• Off-center centromere; “q” arm is longer

• Unequal length

• 13 pairs

• j-shaped

Acrocentric

Chromosome Types: Centromere Position

• means peak

• Very close to one end; yielding a small short arm

• associated with small pieces of DNA called satellites, encoding rRNA

• 5 pairs in humans

• i-shaped

Telocentric

Chromosome Types: Centromere Position

• Centromere at the terminal end

• Not found in humans

Metacentric

Chromosome Types: Arms Ratio

• M/m

• 1.0-1.6/1.7

Submetacentric

Chromosome Types: Arms Ratio

• Sm

• 3.0

Subtelocentric

Chromosome Types: Arms Ratio

• St

• 3.1-6.9

Acrocentric

Chromosome Types: Arms Ratio

• T

• 7.0

Telocentric

Chromosome Types: Arms Ratio

• T

• none

Telomere

Morphology of Chromosomes:

• Tip of each chromosome

TTAGGG

Morphology of Chromosomes: Telomere

• Tandem repeats of the hexameric sequence

end-to-end fusion

Morphology of Chromosomes: Telomere Functions

• Preventing abnormal ___ of chromosomes

degradation

Morphology of Chromosomes: Telomere Functions

• Protecting the ends of chromosomes from ___

DNA replication

Morphology of Chromosomes: Telomere Functions

• Ensuring complete ___

chromosome pairing

Morphology of Chromosomes: Telomere Functions

• Having a role in ___ during meiosis

Individuals with longer telomeres

Morphology of Chromosomes: Telomere

• reported to have a longer subsequent lifespan in some studies of vertebrate species,