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Single Gene Traits: Earlobes

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Hitchhiker. Non-hitcher? T. T. Non-hitcher. T. t. OR. Pair of unduplicated ... two different chromosomes: keeping track of both the hitchhiker and the earlobes! ... – PowerPoint PPT presentation

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Title: Single Gene Traits: Earlobes


1
Single Gene Traits Earlobes
  • phenotype
  • a product/trait resulting from a gene

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

3
Alleles for Earlobe Shape
Attached recessive, f
Free dominant, F
4
gene section of DNA that codes for earlobe shape
5
2 possible alleles attached (f), free (F)
OR
f
F
6
But! You have 2 parents each donated a
chromosome
Dad
Mom
OR
OR
AND
f
F
f
F
7
Genotype
  • genotype
  • the specific set of alleles contained in you

8
Mom
Dad
ff
OR
OR
Ff
Ff
FF
f
F
f
F
9
Describing the allele combination
  • homozygous alleles are the same on homologous
    chromosomes (FF or ff)
  • heterozygous alleles are different (Ff)

10
Homologous chromosomes - code for same set of
genes - occur in pairs, 1 from each
parent Dad Mom
11
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

12
Attached Free
13
Attached Free
recessive, f
dominant, F
14
Individually, build a set of chromosomes to
reflect your genotype draw them.
  • Mom
  • Dad

f
F
15
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
16
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17
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18
sister chromatids
sister chromatids
centromere
19
Clicker What is the correct representation for
the duplicated state of
f
F
B
C
A
E
D
20
Cells Must Divide For
  • Growth (Mitosis)
  • Sex (Meiosis)
  • Copy DNA to ensure that each new cell gets the
    complete set

21
Pair of unduplicated homologous chromosomes
Gene of interest hitchhikers thumb T
straight t hitchhiker
22
Hitchhiker
23
Hitchhiker
t
t
24
Non-hitcher?
25
Non-hitcher
T
T
t
T
OR
26
Pair of unduplicated homologous chromosomes
T
t
1. Build these chromosomes in the duplicated
state.
27
Cell Division by Mitosis
  • Produces identical sister cells
  • 1 diploid cell ? 2 diploid cells

28
T
t
Pair of unduplicated homologous chromosomes
Pair of duplicated homologous chromosomes
t
t
T
T
29
Nucleus
t
t
T
T
Cell
Mitosis
30
t
t
T
T
T
T
Mitosis
t
t
31
Mitosis
T
T
T
T
t
t
t
t
32
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

33
Pair of unduplicated homologous chromosomes
T
t
Build these chromosomes in the duplicated state -
34
t
t
T
T
Meiosis I
35
t
t
T
T
Meiosis I
36
t
t
T
T
Homologs separate
Meiosis I
T
T
t
t
37
T
T
t
t
Meiosis II
38
T
T
t
t
Meiosis II
Sister Chromatids separate
T
t
T
t
39
T
t
T
t
From a heterozygote parent, (genotype Tt) 2
types of gametes formed T or t
40
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.

41
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.

42
Making things a bit more complex
  • Meiosis with two genes found on two different
    chromosomes keeping track of both the
    hitchhiker and the earlobes!

43
Follow along in Mirkov 2 chromosomes, 2 genes,
each with 2 alleles
t
T
f
F
44
Step 1 Chromosomes duplicate
t
t
T
T
f
f
F
F
45
Step 2 Meiosis I Homologs Separate
t
t
T
T
F
f
f
F
46
Step 3 Meiosis I Homologs Separate
t
t
T
T
F
f
f
F
47
Step 4 Meiosis I Homologs Separate ? 2 cells
t
t
T
T
F
F
f
f
48
Step 5 Meiosis II Sister Chromatids Separate
t
t
T
T
f
f
F
F
49
Step 6 Meiosis II Sister Chromatids Separate ?
4 cells
t
T
T
t
F
f
f
F
50
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
51
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
52
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
53
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??
54
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
55
Does meiosis/mitosis make mistakes?
56
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57
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58
  • Trisomy 21 (Downs Syndrome)
  • 1 in 800 live births

59
  • Trisomy 18 (Edwards)
  • 1 in 8,000 pregnancies
  • lt 30 survive 1 month pregnancy

60
  • 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

61
  • Turner Syndrome
  • X (female)
  • underdeveloped female 2ndry sex characteristics
  • short (avg. 48)
  • amenorrhea
  • infertility (non-functional ovaries)
  • spatial/temporal relations

62
Cancer Cells from Female Colon
63
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?
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