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Replicated Chromosomes – identical DNA on sister chromatids which are connected at the centromere PowerPoint Presentation
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Replicated Chromosomes – identical DNA on sister chromatids which are connected at the centromere - PowerPoint PPT Presentation


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q-arm p-arm Replicated Chromosomes – identical DNA on sister chromatids which are connected at the centromere Unreplicated Chromosome Locus – physical location of a gene on a chromosome Ploidy level = # of versions of each chromosome Haploid = 1 version – bacteria, some male insects

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Presentation Transcript
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q-arm

p-arm

Replicated Chromosomes – identical DNA on sister chromatids which are connected at the centromere

Unreplicated Chromosome

Locus– physical location of a gene on a chromosome

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Ploidy level = # of versions of each chromosome

  • Haploid = 1 version – bacteria, some male insects
  • Diploid = 2 versions – we are diploid; one version came from mom, one from dad
  • Polyploid = 3+ versions – many plant species
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A

A

A

a

b

b

b

a

a

b

b

b

Diploid species have homologous pairs of chromosomes

each chromosome in the pair has the same genes, but different alleles

Gene = region of DNA that codes for a specific protein

Allele = a type, or version, of a gene

Cell nucleus in G1 – unreplicated, homologous pairs

heterozygous for Gene A (two different alleles), homozygous for gene B (same alleles)

During S stage of Interphase, DNA is replicated

Sister Chromatids

Homologous Pair

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Chromosomes are located in the . . . . .

Dr. G. Weaver, Colorado University at Denver

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Mitosis begins with one diploid cell with replicated DNA

Mitosis ends with two diploid cells with unreplicated DNA

When is DNA replicated?

How many total copies of each gene are there in metaphase?

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Meiosis begins with one diploid cell with duplicated DNA

Meiosis ends with four haploid cells with unduplicated DNA

How many total copies of each gene are there in Metaphase I? in Metaphase II?

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Crossing Over During Prophase I

  • Leptonema – chromatin begins condensing, search for homologs
  • Zygonema – condensation continues, rough pairing at telomeres (ends)
  • Pachynema – pairing all along chromosomes, chiasmata form, crossing over occurs in some places
  • Diplonema – some decondensation and separation outside of chiasmata, some proteins (like yolk) made – cells can stay in this stage for many years
  • Diakinesis – recondensation, chiasmata marginalized to telomeres so homologs don’t remain attached at centromeres

Importance of crossing over is that no two gametes are identical!

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Haploid (n)

Meiosis

Fertilization

Diploid (2n)

Mitosis