Single Gene Traits: Earlobes

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Single Gene Traits Earlobes

• phenotype
• a product/trait resulting from a gene

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Alleles

• alternative forms of a gene
• we inherit 2 alleles of every gene (1 from mom, 1
  from dad)

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Alleles for Earlobe Shape
Attached recessive, f
Free dominant, F
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gene section of DNA that codes for earlobe shape
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2 possible alleles attached (f), free (F)
OR
f
F
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But! You have 2 parents each donated a
chromosome
Dad
Mom
OR
OR
AND
f
F
f
F
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Genotype

• genotype
• the specific set of alleles contained in you

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Mom
Dad
ff
OR
OR
Ff
Ff
FF
f
F
f
F
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Describing the allele combination

• homozygous alleles are the same on homologous
  chromosomes (FF or ff)
• heterozygous alleles are different (Ff)

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Homologous chromosomes - code for same set of
genes - occur in pairs, 1 from each
parent Dad Mom
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How many homologs of a given chromosome?

• 2 ? Diploid (2n)
• 1 ? Haploid (1n)
• 3 ? Triploid (3n), etc. . .
• where n number of different kinds of chromosomes

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Attached Free
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Attached Free
recessive, f
dominant, F
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Individually, build a set of chromosomes to
reflect your genotype draw them.

• Mom
• Dad

f
F
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Clicker What is the correct representation for
a free-lobed heterozygote whos mother has
attached lobes?
C
B
A
f
F
f
F
f
F
D
E
f
F
f
F
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sister chromatids
sister chromatids
centromere
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Clicker What is the correct representation for
the duplicated state of
f
F
B
C
A
E
D
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Cells Must Divide For

• Growth (Mitosis)
• Sex (Meiosis)
• Copy DNA to ensure that each new cell gets the
  complete set

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Pair of unduplicated homologous chromosomes
Gene of interest hitchhikers thumb T
straight t hitchhiker
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Hitchhiker
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Hitchhiker
t
t
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Non-hitcher?
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Non-hitcher
T
T
t
T
OR
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Pair of unduplicated homologous chromosomes
T
t
1. Build these chromosomes in the duplicated
state.
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Cell Division by Mitosis

• Produces identical sister cells
• 1 diploid cell ? 2 diploid cells

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T
t
Pair of unduplicated homologous chromosomes
Pair of duplicated homologous chromosomes
t
t
T
T
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Nucleus
t
t
T
T
Cell
Mitosis
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t
t
T
T
T
T
Mitosis
t
t
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Mitosis
T
T
T
T
t
t
t
t
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Cell Division by Meiosis

• Produces Gametes (sex cells)
• 1 diploid cell ? 4 haploid cells
• Two Divisions
• Meiosis I Homologs Separate
• Meiosis II Sister Chromatids Separate

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Pair of unduplicated homologous chromosomes
T
t
Build these chromosomes in the duplicated state -
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t
t
T
T
Meiosis I
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t
t
T
T
Meiosis I
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t
t
T
T
Homologs separate
Meiosis I
T
T
t
t
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T
T
t
t
Meiosis II
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T
T
t
t
Meiosis II
Sister Chromatids separate
T
t
T
t
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T
t
T
t
From a heterozygote parent, (genotype Tt) 2
types of gametes formed T or t
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Problem 1 Draw Meiosis for Pair 22

• Use your model to show exactly when and where the
  mistake occurred that resulted in the genotype
  for Trisomy.
• Draw individually - consult with your group.

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Problem 2 Draw the Punnett Square and calculate
the ratios of both phenotypes and genotypes for
the offspring of

• Cross 1 heterozygous female with an
  attached-lobed male.

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Making things a bit more complex

• Meiosis with two genes found on two different
  chromosomes keeping track of both the
  hitchhiker and the earlobes!

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Follow along in Mirkov 2 chromosomes, 2 genes,
each with 2 alleles
t
T
f
F
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Step 1 Chromosomes duplicate
t
t
T
T
f
f
F
F
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Step 2 Meiosis I Homologs Separate
t
t
T
T
F
f
f
F
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Step 3 Meiosis I Homologs Separate
t
t
T
T
F
f
f
F
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Step 4 Meiosis I Homologs Separate ? 2 cells
t
t
T
T
F
F
f
f
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Step 5 Meiosis II Sister Chromatids Separate
t
t
T
T
f
f
F
F
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Step 6 Meiosis II Sister Chromatids Separate ?
4 cells
t
T
T
t
F
f
f
F
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What if homologs lined up differently at Meiosis
1? (Independent Assortment)
t
t
T
T
How many different kinds of gametes could be
formed?
F
f
f
F
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How many different kinds of gametes could be
formed?
T F T f t F t f
t
t
T
T
F
f
f
F
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How many different kinds of gametes could be
formed?
T F T f t F t f 2n
t
t
T
T
(for diploid organisms, where n is the of
homologous pairs in this case n 2)
F
f
f
F
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Humans, n23 so, 223 8,388,608 is the number
of different kinds of gametes 1 person can
make. How many different kinds of zygotes could
2 people form??
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How many different kinds of zygotes could 2
people form?? 8,388,608 x 8,388,608 (or,
8,388,6082) 70,368,744,177,664 !!!! potential
chromosome combinations
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Does meiosis/mitosis make mistakes?
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• Trisomy 21 (Downs Syndrome)
• 1 in 800 live births

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• Trisomy 18 (Edwards)
• 1 in 8,000 pregnancies
• lt 30 survive 1 month pregnancy

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• Klinefelters Syndrome
• XXY (male)
• tall (6 7 )
• hypogonadism
• infertile
• female 2ndry sex characteristics
• infertile (non-motile sperm, if produced)
• sometimes
• osteoporosis
• delayed motor/social/learning skilss

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• Turner Syndrome
• X (female)
• underdeveloped female 2ndry sex characteristics
• short (avg. 48)
• amenorrhea
• infertility (non-functional ovaries)
• spatial/temporal relations

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Cancer Cells from Female Colon
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Predict the outcome of the following crosses.
Draw the Punnett Squares and calculate pheno/geno
ratios.

• 1. 2 free-lobed heterozygotes?
• 2. a male heterozygote with an attached-lobed
  female?
• 3. an attached-lobed female with a free-lobed
  homozygous male?