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,