Cell Division

Chromosome defintion

organized packages of DNA wrapped around histone proteins making sure genetic information is compact, protected, and correctly separated during mitosis and meiosis

How many chromsomes do humans have

• 2 sets of 23

• 46 total

Chromatin defintion

Uncondensed DNA existing in a nucleus during interphase

Sister Chromatid defintion

An identical copy of a chromsome produced during DNA replication

Telomere defintion

Repetitive DNA sequences located at the ends of chromosomes that act as protection

Centromere defintion

Region containing a kinetochore (protein) that attaches sister chromatids

Histone defintion

• protein that DNA wraps around

• help package, organize, and regulate access to DNA inside the nucleus

Nucleosome defintion

• basic structural unit of chromatid

• consisting of a segment of DNA wrapped around a core of histone proteins

Haploid

Single complete set of chromosomes

Diploid

Two copies of genetic material

Homologous Chromosomes definition

a pair of chromosomes (onet from each parent) that have the same genes in the same order and locations

Sex chromsomes

• Pair of chromosomes that contribute to sexual development but also carry non-sex-related genes

• In humans they are X and Y chromsomes

X Chromosome

• Large chromosome with hundreds of genes

• Present in all humans

Y Chromosome

• Much smaller than the X chromosome and contains fewer genes

• Activates genes involved in typical male developmental pathways during early embryonic development

Mitosis

• Produces genetically identical diploid cells in somatic cells

• Maintains chromosome number

• Enables growth, tissue repair, and cell replacement in multicellular organisms

• Supports asexual reproduction

Meiosis

• Produces haploid gametes

• Reduces chromosome number by half

• Generates genetic variation through crossing over and independent assortment

• Ensures genetic diversity, increasing a population’s ability to adapt and evolve

• Creates genetically unique cells

Cell cycle steps

• G0

• Growth 1

  • Growth / development

• S Phase

  • DNA replication

• Growth 2

  • Prep for cell division

Mitosis stages

• Prophase

• Metaphase

• Anaphase

• Telophase

• Cytokinesis

Prophase

• Nuclear envelope degenerates

• Chromatin condenses into chromosomes

• Replicated chromosomes pair up

• Spindle fibers form

Metaphase

• Replicated chromosomes line up at metaphase plate

• Centrosomes move to cellular poles

• Spindle fibers attach at centromeres

Anaphase

• Spindle fibers shorten and pull apart sister chromatids towards opposite poles

Telophase

• Nuclear envelopes reform

• Spindle fibers release from centromeres

• Actin and Myosin filaments around membrane constrict and create a cleavage furrow

Cytokinesis

• Cellular membranes separate when furrow meets

• Chromosomes decondense to chromatin

Meiosis 1 vs 2

• Meiosis 1 is a reductional division

• Meisois 2 is an equational division

Prophase 1

• Nuclear membrane degenerates

• Chromatin condenses

• Chromosomes line up with homologous pair at centromere

• Homologous chromosome pairs create tetrads

• Spindle fibers form

• Crossing over occurs

Crossing over

• Main reason for unique attributes

• Segments of homologous chromosomes swap with each other to create recombinant chromosomes

• happens at chiasmata

Metaphase 1

• Tetrads of recombinant chromosomes line up along metaphase plate

• Spindle fibers attach at centromere

• Centrosomes to move poles of cell

• Independent assortment of chromosomes

Independent Assortment

• How one homologous pair lines up has no effect on how another pair lines up

Anaphase 1

• Spindle fibers shorten and pull homologous pairs apart towards opposite poles

Telophase 1

• Nuclear envelope reforms

• Myosin and actin constrict to form cleavage furrow

• Spindle fibers release from centromeres

Cytokinesis 1

• Daughter cells separate when furrow meets

• Chromosomes decodense to chromatin

Prophase 2

• Nuclear envelope degenerates

• Chromatin condenses into homologous chromosomes, attached at centromere

• Spindle fibers form

Metaphase 2

• Homologous chromosomes line up on metaphase plate

• Spindle fibers attach at centromere

• Centrioles move to poles of cell

Anaphase 2

• Spindle fibers shorten, pulling sister chromatids apart towards poles of cell

Telophase 2

• Nuclear membrane reforms

• Myosin and actin constrict to form cleavage furrow

• Spindle fibers release from centromeres

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Cytokinesis 2

• Daughter cells separate when furrow meets

• Chromosomes decondense into chromatin

Spermatogenesis

• Occurs in testes

• One diplod cells = 4 functional sperm

• Continuous after puberty

• Equal division

Oogenesis

• Occurs in ovaries

• One diploid cell → 1 egg + polar bodies

• Unequal cytokinesis

• Begins before birth

What do karyotypes show us

• Total chromosome number

• Homologous chromosome pairs

• Sex chromosomes

• Large-scale chromosomal abnormalities

  • Extra or missing chromosomes

  • Large deletions or duplications

How are karyotypes made

• Cells are collected and paused in metaphase

• Chromosomes are condensed

• Chromsomes are…

  • Stained

  • Photographed

  • Matched into homologous pairs

Nondisjunction

• failure of homologous chromosomes or sister chromatids to separate properly during meiosis or mitosis

• results in daughter cells with abnormal chromosome numbers

• Results in developmental disorders

Translocation

Chromosomal abnormality where part of a chromosome breaks off and attaches to another chromosome

Reciprocal Translocation

When two non-homologous chromosomes swap arms with each other

Deletion

When a segment of DNA is missing from a chromosome

Inversion

When a chromosome breaks in 2 parts, detaches, rotates 180 degrees, and reattaches