5 Chromosomes

Cytogenetics

How chromosomes relate to cell behavior particularly to their behavior in mitosis and meiosis

DNA

Within the human nucleus and it is organized into what we call the chromosome

Chromosome

located inside the nucleus that is capable of self reproduction and plays a vital role in heredity mutation variation and evolutionary development of species

mitotic

chromosomes are Present in the nuclei of cells but are only detectable during the _____ stage.

chroma
color
soma
body

CHROMOSOMES

Origin (Greek language): "____" (____), "____" (____).

Waldeyer
1888

CHROMOSOMES Introduced by _____ in ____.

dna and protein

CHROMOSOMES composition

Heterochromatin

Closed Chromatin, is densely packed, and transcription cannot occur.

Euchromatin

Open Chromatin, is loosely packed, and transcription can occur

46

CHROMOSOME NUMBER In humans:

Each somatic cell has __ chromosomes, referred to as the diploid set (2n).

23

CHROMOSOME NUMBER In humans:

Gametes have __ chromosomes, referred to as the haploid set (n).

Autosomes

(44) Consists of 22 pairs of chromosomes that are exactly alike (homologous); one chromosome of each pair comes from the father, the other from the mother

Sex chromosomes

(2) Composed of two different kinds: X and Y.

Homologous chromosomes

Are chromosome pairs that have the same genes and similar genetic content.

Have the same gene loci, although they may have different alleles for those genes.

0.2-50 µm

human 4-6 µm

chromosome length

0.2–20 µm

chromosome diameter

Resting/Interphase

Chromosomes occur in the form of thin, coiled, elastic, and contractile thread-like stainable structures called chromatin threads.

Metaphase/Anaphase

Chromosomes become thick and filamentous.

nucleosome

Chromosomes are organized into a structure that looks like a beaded string, with each bead called a _______.

solenoid

During normal cell activity (interphase), the DNA is somewhat coiled into a structure called a ______.

histone H1

coiling is supported by a protein called _____ __.

5

coiling reduces the DNA's length by about _ times, making it more manageable.

100

When cells are preparing to divide (mitosis or meiosis), the chromosomes condense even more, making them about ___ times smaller.

Chromatid

One of the two identical halves of a chromosome that has been replicated in preparation for cell division.

centromere
spindle fibers

The two chromatids are held together at the ______, a localized region of the chromosome in which ______ ______ attach.

kinetochore
primary constriction

centromere Also called ___ or ___ _______.

H2A, H2B, H3, H4

Nucleosome core particle

Histones

Positively charged and can make ionic bonds with negatively charged phosphate groups in the DNA

Deoxyribonucleic Acid

Primary constituent of chromatin

Heterochromatin

Dark-staining coiled portions

More condensed

Silenced genes (methylated)

Gene poor (high AT content)

Euchromatin

Light-staining extended portions

Less condensed

Gene expressing

Gene rich (higher GC content)

Metacentric
Sub-metacentric
Acrocentric
Telocentric

CLASSIFICATION OF CHROMOSOMES According to Position of Centromere

Metacentric

Centromere located near the center; arms have almost equal lengths.

Sub-metacentric

Centromere slightly away from the center, forming a short arm and a long arm.

Acrocentric

Centromere is very close to one end, producing a very short arm and a long arm.

Telocentric

Centromere is at one end, causing the chromosome to have only one arm. Human does not have it.

Monocentric
Dicentric
Polycentric
Acentric

According to Number of Centromere

Monocentric

Single centromere

Dicentric

Two centromeres

Polycentric

Multiple centromeres

Acentric

Lacks a centromere

centromere
bands

According to the Paris Nomenclature:

In this method, the long and short arms of a chromosome are divided into regions starting from the ___, which are further subdivided into ___.