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Biology LibreTexts

2.S: Chromosomes, Mitosis, and Meiosis (Summary)

  • Chromosomes are complex and dynamic structures consisting of DNA and proteins (chromatin).
  • The degree of chromatin compaction involves proteins and varies between heterochromatic and euchromatic regions and among stages of the cell cycle.
  • Chromosomes can be distinguished cytologicaly based on their length, centromere position, and banding patterns when stained dyes or labeled with sequence-specific probes.
  • Homologous chromosomes contain the same series of genes along their length, but not necessarily the same alleles.Sister chromatids initially contain the same alleles.
  • Chromosomes are replicated by DNA polymerases and begin at an origin. Replication is bi-directional. Eukaryotes have multiple origins along each chromosome and have telomerase to replicate the ends.
  • Mitosis reduces the c-number, but not the n-number.Meiosis reduces both c and n.
  • Homologous chromosomes pair (sysnapse) with each other during meiosis, but not mitosis.
  • Several types of structural defects in chromosomes occur naturally, and can affect cellular function and even evolution.
  • Aneuploidy results from the addition or subtraction of one or more chromosomes from a group of homologs, and is usually deleterious to the cell.
  • Polyploidy is the presence of more than two complete sets of chromosomes in a genome.Even-numbered multiple sets of chromosomes can be stably inherited in some species, especially plants.
  • Endopolyploidy is tissue-specific type of polyploidy observed in some species, including diploids.
  • Both aneuploidy and structural defects such as duplications can affect gene balance.
  • Organelles also contain chromosomes, but these are much more like prokaryotic chromosomes than the nuclear chromosomes of eukaryotes.

Key Terms

chromosome

core histones

nucleosome

30nm fiber

histone H1

scaffold proteins

heterochromatin

euchromatin

satellite DNA

chromatid

centromere

metacentric

acrocentric

telocentric

holocentric

telomere

homologous

non-homologous

chromatid

sister chromatid

non-sister chromatid

interphase

mitosis

prophase

metaphase

anaphase

telophase

DNA polymerase

origin of replication

telomerase

riboprotein

Hayflick limit

HeLa cells

cytokinesis

meiosis

gametes

prophase (I, II)

metaphase (I, II)

anaphase (I, II)

telophase (I, II)

cytokinesis

meiocyte

bivalent

syanapse, pair up

synaptonemal complex

reductional division

equational division

leptotene

zygotene

pachytene

diplotene

diakinesis

crossing over

chiasma (chiasmata)

polar bodies

G1

G2

S

M

G0

interphase

n

c

replicated chromosome

karyotype/karyogram

autosome

sex-chromosome

homogametic

heterogametic

aneuploidy

monsomic

trisomic

Down syndrome

deletion

duplication

insertion

inversion

translocation

non-disjunction

chromosome breakage

polyploidy

x

monoploid

sterile

tetravalent

octoploid

hexaploid

triploid

endoreduplication

endopolyploidy

salivary gland chromosome

polytene

gene balance

cellular network

chloroplast

mitochondria

endosymbiont

endosymbiont theory

organellar chromosome

mtDNA

 

 

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