Crossing Over Manipulative

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Crossing Over Manipulative Lab

• Crossing Over SHOULD ONLY occur between
  Homologous Chomosomes during Meiosis
• Oogenesis - the creation of an egg/ovum
• Spermatogenesis - the creation of sperm

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Chromosomes
Homologous chromosomes

• Chromosome 1

Preparing to divide
Crossing over
A mixing of genetic traits
mom
2 pairs of sister chromatids a tetrad
dad
Karyotype of chromosomes With fluorescent markers
at gene sites
3
Meiosis - production of gametes
Interphase
What 3 things happen here?
Synapsis - pairing of homologous chromosomes
Chiasma - point where crossing over occurs
Prophase I
Haploid (n) or Diploid (2N)?
Haploid (n) or Diploid (2N)?
Metaphase I
Anaphase I
Haploid (n) or Diploid (2N)?
Telophase I
Prophase II
No Interphase between Meiosis I and Meiosis II,
means that G1, S, and G2 do not occur.
Metaphase II
What is the end result in terms Of the chromosome
number?
Anaphase II
Telophase II
4 genetically unique sperm
4 genetically unique cells 1 egg 3 smaller polar
bodies
Haploid (n) or Diploid (2N)?
4
Genes - genetic instruction determining
traits/characteristics
turned on (expressed) or turned off
Shy, outgoing, friendly, introverted, extroverted,
quiet, bubbly, funny, intellectual, secretive,
stoic, silly, charming, energetic, kind, loyal,
reliable, moody, sociable, thoughtful, witty,
stubborn, vain, gullible, impulsive, domineering
Gene loci
Artist Amateur Doodlist
X
Hair color
centromere
Eye color
ethnicity
Musician Amateur Listener
height
Describing YOUR traits!
Artistic
hand
Brilliant Smart Average
Music
IQ
personality
Olympian Jock Spectator
Athletic ability
Hair type
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Homologous Chromosomes
X
X
Each tetrad provides information about the same
trait
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Homologous Chromosomes Crossing Over
X
X
Each tetrad provides information about the same
trait
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Crossing Over
Are the gametes genetically the same as each
other or unique?
Dad
Mom
X
X
Separate the gametes tetrad, draw them down id
person
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Crossing Over

• Mixing the Gene Pool!
• Separating Exchanging Genes

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Chromosome Genes Loci Traits Alleles Dominant Rece
ssive Homozygous Heterozygous Hybrid
Chromosome 1
a
a
A
A
b
b
b
b
c
c
c
c
D
d
D
d
E
E
E
E
f
F
f
F
g
g
G
G
h
h
h
h
i
i
i
i
j
J
j
J
K
k
K
k
Identical sister chromatids
Identical sister chromatids
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Chromosomal Errors
Philadelphia Chromosomes
During Meioisis, Crossing Over between
Homologous Chromosomes but not at the same place
missing info and extra info Shows up in EVERY
Cell of the person
During Mitosis, Translocation between
Non-Homologous Chromosomes shows up only in the
cells that have undergone the error during mitosis
Junction - come together Disjunction - dont come
together Non-Disjunction - come together even
when youre not supposed to?
Non-Disjunction
Down Syndrome (21)
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And more variation

• Crossing over
• Typically 1 - 3 cross overs per chromosome
• creates completely new combinations of traits
  in next generation
• 223 8.4 million possible chromosomal
  combinations due to independent assortment

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Random fertilization

• Any 2 parents will produce a zygote with
• (223 x 223) over 70 trillion diploid
  combinations

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Sexual reproduction creates variability

• Sexual reproduction allows us to maintain
• both genetic similarity differences.

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