Download - Crazy Chromosomes!
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Crazy Chromosomes!
Ch. 15
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Journal
• How many pairs of chromosomes are there per cell? Which law of Mendel’s produces this specific number?
• What occurs during nondisjunction? Name a disorder caused by nondisjuntion
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Nondisjunction
• Results in aneuploidy = zygote with abnormal chromosome #
• Monosomic When zygote has only 1 copy of a gene (2n – 1)
• Trisomic When zygote has 1 additional copy of a gene (2n + 1)
VIDEO
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Trisomy 21
• Trisomy 21 (AKA Down Syndrome) • A common trisomic genetic disorder caused by
extra 21st chromosome
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Alterations of Chromosomes
What might cause chromosomes to alter their genetic sequence?
errors during meiosis or damage like radiation
4 way to alter sequence:
1) Deletion
2) Duplication
3) Inversion
4) Translocation
Occur during synapsis
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Chromosome Alterations PIC
All can be harmful because can either be lethal or alter individual phenoype by making different/faulty protein
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Disorders from Alterations
*Many are so dangerous = spontaneously abortion
1) Aneuploidy of Sex ChromosomesA. XXY (1 in 500-1000 males) - Klinefelter Syndrome
- affects male sex organs causes male to be infertile
- may develop female characteristics
B. X (1 in 2500) monosomy X (Turner Syndrome)
-sterile females sex organs not mature
C. XYY (1 in 1000 males)
- develop normally… may be taller than average
D. XXX (1 in 1000 females) - trisomy X
-develop normally… may be taller than average
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Aneuploidy of Sex ChromosomesPICS
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Disorders from Alterations
*Many are so dangerous = spontaneously abortion
2) Structurally Altered Chromosome DisordersA. Cri du chat (“cry of the cat”) – deletion on chromosome 5
- severely intellectually disabled- small head, unusual facial features- cry like distressed cat (video) usually die as infants early
childhood
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Chromosomes outside the nucleus… Huh? What? No Way!Inheritance of organelle genes
What organelle(s) would have their own genes?
Why might this be?
Mitochondrial DNA – a small portion of your DNA that only comes from mom … how can this be?
can be used to trace lineage
you and your siblings and your mother all have identical mitochondrial DNA!
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Mitochondrial DNA … beneficial or harmful for males?
ARTICLE
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Linked Genes
What are linked genes?
How do they differ from sex-linked genes?
How would you relate linked genes to Mendel’s law of independent assortment? What is the relationship?
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Linked Genes
DO GENES ALWAYS STAY LINKED?
in other words
ARE LINKED GENES ALWAYS INHERITED TOGETHER?
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Genetic Recombination and Linkage
• In pea plants, yellow seeds are dominant to green seeds and round seeds are dominant to wrinkled. Perform a dihybrid cross between a homozygous recessive plant and a plant that is heterozygous for both traits.
• ½ share same genotype as parents = Parental Type
• ½ share different genotype than parents = recombinantsWe say that there is a 50% frequency of recombinants when
these two plants are crossedThis is a common outcome for unlinked genes that undergo
I.A.
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Genetic Recombination and Linkage
• Morgan’s fly testing showed that only 17% of his believed to be “linked” genes showed recombinants
• Concluded that sometimes these linked genes can become unlinked!• This occurs during what we now call crossing over
(synapsis)
• This creates new combinations of chromosomes (by splitting linked genes)
DRIVING DIVERSITY and ultimately NATURAL SELECTION among a species
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Genetic Mapping
• One of Morgan’s students, Alfred Sturtevant predicted that the farther apart 2 genes are, the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency.
• Let’s look at an example
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Sturtevant’s linkage map of 3 genes in Drosophila
• 3 genes: body-color (b), wing-size (vg), and cinnebar (cn) –one of many genes affecting eye color
• Observed recombination frequencies:• cn and b = 9%• cn and vg = 9.5%• b and vg = 17%
*Crossing over would occur most frequently between genes b and vg
• He decided to “map” these out on a chromosome• 1 map unit is = to 1%
recombination frequency
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Sturtevant’s linkage map of 3 genes in Drosophila
• Let’s practice!
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Linkage Practice
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A Wild type fruit fly (heterozygous for gray body and normal wings) is mated with a black fly with vestigial wings.OFFSPRING: 778- wild type785- black-vestigial158- black- normal wings162- gray body-vestigial wings
What is the recombination frequency between these genes?
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A Wild type fruit fly (heterozygous for gray body and red eyes) is mated with a black fly with purple eyes.OFFSPRING: 721- gray body/red eyes751- black body/purple eyes49- gray body/purple eyes45- black body/red-eyes
What is the recombination frequency between these genes?
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Determine the sequence of genes along a chromosome based on the following recombination frequencies:A-B = 8 map unitsA-C = 28 map unitsA-D = 25 map unitsB-C = 20 map unitsB-D = 33 map units
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Determine the sequence of genes along a chromosome based on the following recombination frequencies:A-C = 20 map unitsA-D = 10 map unitsB-C = 15 map unitsB-D = 5 map units