Genome: Complete complement of an organisms DNA. Includes genes
(control traits) and non-coding DNA organized in chromosomes. 2
Genome > Chromosome > DNA > Genes
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Eukaryotic DNA is organized in chromosomes. Genes have specific
places on chromosomes. 3
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Heredity way of transferring genetic information to offspring
Chromosome theory of heredity: chromosomes carry genes. Gene unit
of heredity. 4
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Asexual: self-reproducing, produce clones (offspring
genetically identical to parent) Many single-celled organisms
reproduce by splitting, budding, parthenogenesis. Some
multicellular organisms can reproduce asexually. 5
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Fusion of two gametes to produce a single zygote. With
exception of self-fertilizing organisms (e.g. some plants), zygote
has gametes from two different parents. 6
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Total = 46 chromosomes (23 pairs) 44 autosomes + 2 sex
chromosomes 8
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Autosomes: Code for most genes in your body (not sex
determining chromosomes) In humans chromosome #1-22
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Sex Chromosomes: chromosomes that determine what gender you
will be. #23 in humans Females are: XX Males are XY
Slide 11
Gametes: sperm/egg haploid (n) Haploid= Contains a single set
of chromosomes (23) Zygote: fertilized egg now diploid (2n)
Diploid= Contains a two sets of chromosomes (23x2=46) Somatic cell:
any cell other than gametes, most of the cells in the body. All are
diploid (2n) Meiosis KM11
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Mammals use a chromosomal method of determining sex: XX is
female and XY is male. Birds use a ZW system: ZZ is male and ZW is
female. the evolutionary origin of mammalian and bird sex
chromosomes is different Some reptiles use developmental
temperature to determine sex: depends on the species, but hot is
male and cold is female in some.
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Chromosomes exist in homologous pairs in diploid cells.
homologous pairs: chromosomes that code for the same genes but
possibly have different alleles (get one from each parent) 13
Exception: Sex chromosomes (X, Y). All autosomes are in homologous
pairs.
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Meiosis KM14 Now each homologous chromosome has a sister
chromatid Still considered diploid (2n) cell because still just two
copies of each chromosome (even though they now have a twin)
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Meiosis KM15
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Meiosis KM16
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17 All are even numbers diploid (2n) sets of homologous
chromosomes! Ploidy = number of copies of each chromosome.
Diploidy
Slide 18
Meiosis: cell division process by which the number of
chromosomes per cell is cut in half Why does it occur: Meiosis is
used to produce the haploid(n) gametes (sperm and eggs) 18
Slide 19
Meiosis reduces the number of chromosomes by half. Daughter
cells differ from parent, and each other. Meiosis involves two
divisions, Mitosis only one. 19
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Meiosis KM20
Slide 21
Meiosis KM21
Slide 22
First division of meiosis Prophase 1: Duplicated homologous
chromosomes match up forming tetrads. Crossing-over occurs at the
chiasmata. Crossing-over Metaphase 1: Tetrads align at the equator
of the cell. Anaphase 1: Homologous pairs separate with sister
chromatids remaining together. Telophase 1: Two daughter cells are
formed with each daughter containing only one chromosome of the
homologous pair. 22
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23
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24 produces recombinant chromosomes, mixing the genes of the
mother and father, recombining them. Occurs during Prophase 1
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Meiosis KM25
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Second division of meiosis: Gamete formation Prophase 2: DNA
does not replicate. Metaphase 2: Chromosomes line up at the
equatorial. Anaphase 2: Sister chromatids move separately to
opposite ends of the cell. Telophase 2: Cell division is complete.
Four haploid(n) daughter cells are produced. 27
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Meiosis KM29
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Meiosis KM30
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During normal cell growth, mitosis produces daughter cells
identical to parent cell (2n to 2n) Meiosis results in genetic
variation by: Shuffling of maternal and paternal chromosomes and
crossing over. No daughter cells formed during meiosis are
genetically identical to either mother or father During sexual
reproduction, fusion of the unique haploid gametes produces truly
unique offspring. 31
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Meiosis KM32
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Number of combinations: 2 n 33 e.g. if there are 2 chromosomes
in haploid 2n = 4; n = 2 2 n = 2 2 = 4 possible combinations
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34 e.g. 23 chromosomes in haploid 2n = 46; n = 23 2 n = 2 23 =
~ 8 million possible combinations!
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At least 8 million combinations from Mom, and another 8 million
from Dad >64 trillion combinations for a diploid zygote!!!
Meiosis KM35
Slide 36
In males, all 4 products of meiosis develop into sperm cells.
They lose most of their cytoplasm, remodel their cell shape, and
grow a long flagellum (tail). Male gamete formation -
Spermatogenesis
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In females, most of the cytoplasm goes into 1 of the 4 meiotic
products, which becomes the egg. The other 3 meiotic cells are
small polar bodies, which degenerate. Female gamete formation -
Oogenesis
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More genetic diversity: more potential for survival of species
when environmental conditions change. Shuffling of genes in meiosis
Crossing-over in meiosis Fertilization: combines genes from 2
separate individuals DNA back-up and repair. Asexual organisms
don't have back-up copies of genes, sexual organisms have 2 sets of
chromosomes and one can act as a back-up if the other is damaged.
(some organisms have more) Sexual mechanisms, especially
recombination, are used to repair damaged DNA - the undamaged
chromosome acts as a template and eventually both chromosomes end
up with the correct gene. 38
Slide 39
1. How does metaphase of mitosis differ from metaphase I of
meiosis? 2. What happens as homologous chromosomes pair up during
prophase I of meiosis? 3. What is the sole purpose of meiosis? 4.
What specific activities, involving DNA, occur during interphase
prior to both mitosis and meiosis? 5. Compare mitosis and meiosis
on the following points: a. number of daughter cells produced. b.
the amount of DNA in the daughter v. parent cell c. mechanism for
introducing genetic variation. 6. What is a zygote and how is it
formed? 39
Slide 40
Summarize the process of meiosis in 5 sentences or less
(include the following in your summary) What is the sole purpose of
Meiosis? What does it start with and what does it end with (include
males and females) Use and underline vocab words gamete, diploid,
haploid, crossing over, and homologous pairs, and sister chromatids
40