Chromatin structure

Centromere

constricted region of the chromosome that separates it into a short arm (p) and a long arm (q). The Kinetochore assembles at the centromere. Cohesion proteins are concentrated near there centromere. Location is determined epigenetically

Kinetochore formation

forms at the centromere. it is a protein complex. acts as the attachment site for spindle fibers during cell division ensuring accurate segregation of chromosomes to daughter cells

Cohesion proteins

hold sister chromatids together and are concentrate near the centromere. Makes the “pinched” appearance. ensures that the chromosomes are evenly divided, preventing errors that could lead to condition such as aneuploidy

Telomere

at he ends of chromosome. Specialized nucleoprotein caps composed of repetitive DNA sequence and associated proteins that maintain chromosome integrity and stability by preventing chromosomes ends from being recognized as DNA damage

Human NA sequence of a telomere

TTAGGG

Roles of Telomere

1) prevent the loss of essential genetic information during DNA replication 2) protects against fusion, degradation, or inappropriate repair mechanisms

Fact about cell division and telomeres

after each cell diviosn, telomeres shorten because DNA polymerase cannot full replicate the very ends of chromosomes “end-replication problem” Excessive shortening eventually leads to loss of genes and cellular senescence, contributing to aging, genetic disorders, cancer\T

Telomerase in cancer

telomerase is an enzyme that extends telomeres. In cancer telomerase is reactivated which allows uncontrolled cell proliferation

Chromsome

1. thread-like structure located inside the nucleus of a cell, composed of DNA tightly coiled around proteins

2. A discrete unit of the genome carrying many genes. Each chromosome consists of a very long molecule of duplex DNA and an approximately equal mass of proteins, and is visible as a morphological entity only during cell division

Chromatid

one of the two identical halves of a chromosome that are created when a chromosome replicates

Sister Chromatids

identical copies of a chromosome that are joined at the centromere

Daughter chromatids

individual DNA strands (chromatids that result from the separation of sister chromatic during cell division

Locus

the position on a chromosome at which the gene for a particular trait resides; it may be occupied by any one of there alleles for the gene

Genes

a segment of DNA that contains information for making proteins that ultimately decide traits

Structural gene

a gene that encodes any RNA or polypeptide product other than a regulator

regulatory gene

a gene that encodes a protein involved in the expression of structural or non-structural genes

Alleles

variants of a gene that determine traits

karyotyping

is the process of visualizing and analyzing the number, size, shape, and structure of chromosomes

How many chromosomes do humans have

23 pairs of chromosomes

How many chromosomes do dogs have

39 pairs of chromosomes, a total of 78 chromosomes

How many chromosomes do cats have

19 pairs of chromosomes, total of 38 chromosomes

All cats except Ocelot and Geoffroy have 38 chromosomes. How many chromosomes do the Ocelot and Geoffroy’s cat have

36 chromosomes

Karyotyping (Ideogram)

1. Graph representing karyotypes or chromosomal banding patterns

2. Chromsomes are typically prepared from dividing cells like blood lymphocytes), stained with Giemsa stain like G-bading and analyzed under a brightfieqld microscope at high magnification

3. Dark area in G-banding is AT rich and light area is GC rich

Autosomes

chromosomes that do not decide gender

sec-chromosomes

chromosomes that decide gender

Telocentric

centromere that is located at the tip of the chromosome appearing as a single arm

Acrocentric

centromere is positioned very near to one end, creating one very long arm and one very short arm

Submetacentric

centromere is slightly off-center, resulting in one longer arm and one shorter arm

Metacentric

centromere is located in the middle of the chromosome, creating two equal-sized arms

Ploidy

number of complete sets of chromosomes in a cell or an organism

Haploid

single set of unpaired chromosomes in a cell or an organism from one parent

examples of haploid

gametes in animals and humans

male bees, ants, and wasps (which develop from unfertilized eggs)

Moss and fungi during certain stages of their life cycle

Diploid

two sets of chromosomes in a cell or an organism from each parent

example of diploid

most animals including humans (somatic cells are diploid)

many plants (wheat and maize in their vegetative state)

polyploidy

more than two sets of chromosomes in a cell or an organism triploid, tetraploid, hexapod, octaploid(

Triploid

three sets of chromosomes in a cell or an organism

examples of triploid

seedless watermelon and bananas

certain amphibians and fish

Hexaploid

six sets of chromosomes in cell or an organism

Aneuploid

A condition where the number of chromosomes is not an exact multiple of a complete set due to the gain or loss of chromosomes

Examples of Aneuploid

trisomy and monosomy

trisomy

gain of one chromosome

example of trisomy

down syndrome (trisomy 21 +1) in humans

Monosomy

complete or partially missing one chromosome

example of monosomy

turner syndrome

Monoploid

different from haploid: a single set of chromosomes in organism that are normally diploid

what are the two types of chromosomal mutation

1. chromosomal structural mutation

2. chromosomal numerical nutation

what are the sub types of chromosomal mutation

translocation, inversion, deletion, duplication, missing chromosome(s)(Monosomy) extra chromosome(s)(trisomy), duplication

what is the difference between A compartment and B compartment

A compartment: high gene density, found mostly in center of nucleus

B compartment: low gene density, attacked to the lamina

what is F-actin

help move, organize and protect chromosomes during cell division and DNA repair

lamina

lines the inner surface of the nucleus

Non-random nuclear organization

each chromosome occupies a territory in the interphase nucleus rather than being randomly entangled with others

chromosome territory are established after mitosis

chromosome territories are reestablish during early G1 after mitotic exit an remain relatively stable throughout interphase

Gene density matters

gene-rich chromosomes tend to localize toward the center of the nucleus and gene-poor chromosomes are more often near the nuclear periphery

Functional relevance to gene regulation

territorial positioning influences transcriptional activity, DNA replication timing, and access to transcription machinery

Dynamic but contained chromosomal territories

chromosomes show limited movement within their territory, allowing regulated interchromsomal interactions without losing overall organization