Inheritance: Mendelian Genetics

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Inheritance Mendelian Genetics
I. Gregor Mendel (1865) A. Before Mendel B.
Mendels experimental approach II. Genetic
terms 1. genes 2. gene pair 3. alleles 4.
homozygous/heterozygous 5. dominant/recessive 6.
homozygous dominant and recessive/heterozygous 7
. genotype/phenotype III. Genetic crosses A.
Monohybrid crosses B. Dihybrid crosses IV.
Mendel's discoveries A. Principle of
segregation B. Principle of independent
assortment C. Genes are particles
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A. Before Mendel
Darwin and Mendel
The blending theory (paradigm)
Inheritance of acquired characteristics

• statistics

• amateur

• inductive leap

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B. Mendels experimental approach
Hermaphrodite
Perfect flowers
Genetic barriers
pollen
egg
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Pea plant traits
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Pure breeding lines
Breed true
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• Why was Mendels experimental findings ignored
  during
• his lifetime?
• He was an amateur
• There was a problem with inductive leaps
• The dominant paradigm was opposed to his findings
• He used statistics
• All of the above

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II. Genetic terms
1. genes/ loci 2. gene pair homologues 3.
alleles 4. homozygous/heterozygous 5.
dominant/recessive 6. homozygous dominant and
recessive/heterozygous 7. genotype/phenotype
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Human traits
Hand folding
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III. Genetic crosses
Punnett Square
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III. Genetic crosses
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Red coat in foxes is a dominant trait white is
the recessive trait. If a red fox whose mother
had a white coat is bred to a white fox, what
will be the probable percentage of red kits
(baby foxes)? a. 25 b. 50 c. 75 d. 100
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Monohybrid cross genetic disorders and lethal
genes
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• Tay-Sachs is a lethal disorder resulting in death
  by the
• age of 4. A couple who are normal have a child
  with Tay-
• Sachs. Which of the following is true of the
  parents?
• One parent is homozygous dominant and the other
  is
• homozygous recessive
• b. both parents are heterozygous
• c. both parents are homozygous dominant
• d. both parents are homozygous recessive

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Sickle cell trait recessive disorder
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Sickle cell trait recessive disorder
Homozygous dominant normal, not malaria
resistant
Heterozygous malaria resistant
Homozygous recessive sickle cell anemia
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Huntingtons disease dominant disorder
CAGCAGCAG
Normal, 26 times
HD, 40 to gt100 times
Manifests after age 40
Why is dominant lethality less common than
recessive?
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Dwarfism dominant trait
Homozygous dominant lethal
Heterozygous dwarf
Homozygous recessive normal height
Hardy-Weinburg rule
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If two achondroplasic dwarfs have children, what
fraction of the children would be expected to be
dwarfs like their parents? a. 1/4 b. 1/2 c.
2/3 d. 3/4

• What determines how common a trait is in a
  population?
• its frequency
• Dominance
• Selection
• Chance

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B. Dihybrid crosses Human traits
Dark hair dominant to light hair
Curly hair incompletely dominant to straight hair
Brown eyes dominant to blue
Dimples dominant to no dimples
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In humans, a widow's peak is dominant and a
straight hairline is recessive. Dimples are
dominant and no dimples are recessive. A male
who is heterozygous for both widow's peak and
dimples has a child with a woman who has a
straight hairline and no dimples. What is the
phenotype ratio of children can they produce? a.
3 1 b. 22 c. 1111 d. 40
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IV. Mendels discoveries
A. Principle of segregation
Sexually reproducing diploid organisms have 2
alleles of each gene. These 2 alleles segregate
from each other to form gametes that contain
only 1 allele of each gene.
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B. Principle of independent assortment
Different genes on different chromosomes
segregate into gametes independently of each
other.
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• Mendels Principle of Segregation is based on
  which
• event in meiosis?
• Anaphase I
• Anaphase II
• Metaphase I
• Metaphase II

Mendels principle of Independent Assortment is
based on which event in meiosis? a. Anaphase I b.
Anaphase II c. Metaphase I d. Metaphase II
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C. Genes are particles
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V. Eugenics
Social Darwinism
Francis Galton
Positive Eugenics
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Eugenics
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Eugenics
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Eugenics today?
IVF/ PGD
Gene therapy
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Non-Mendelian Inheritance
I. Dominance relations A. Incomplete
dominance B. Codominance II. Interactions
between different gene pairs epistasis III.Multip
le effects of single genes pleiotropy IV.
Environmental effects on phenotype V. Polygenic
inheritance VI. Sex chromosomes VII.Linkage and
crossing overVIII. Genes and behavior
A. Incomplete dominance
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B. Co-dominance
Bombay phenotype
ABO blood typing system
Three alleles
IA, IB, i
Rh factor is completely dominant trait (R, r)
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Blood type by population
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• Jack has B blood and Jill has A- blood. Their
  daughter,
• Jenna has B- blood. What is Jacks genotype?
• Heterozygous for B and heterozygous for Rh
• Homozygous dominant for B and heterozygous for Rh
• Heterozygous for B and homozygous for Rh
• Cannot tell from this information

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II. Epistasis
One gene pair masks the expression of another
gene pair
B and E genes
Black B_ E_
Chocolate bb E_
Yellow _ _ ee
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A black lab female whose mother was yellow and
father was chocolate has a litter of puppies
sired by a chocolate male whose father was a
yellow lab. What is the probability that one of
the puppies will be a yellow lab? a. 1/8 b.
¼ c. ½ d. ¾
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III. Pleiotropy
One gene has multiple effects pigmentation and
eye convergence
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IV. Environmental effects on phenotype
Height of American school-age children
Siamese cats
Cortisol and stress
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V. Polygenic Inheritance
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V. Polygenic Inheritance skin color
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V. Polygenic Inheritance eye color
Eye color two master genes
Brown/blue and Green/blue
Three modifier genes
Density of pigment
Distribution of pigment
Tone of pigment
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V. Polygenic Inheritance
The result of polygenic inheritance is continuous
variation.
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VI. Sex chromosomes
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VI. Sex chromosomes
Y genes

• Y

• 78 genes

• 95 junk

• SRY

• anti-mullerian

• sperm production

• housekeeping genes

• inversion region

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Y Genes
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Y evolution
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X

• Disease genes

• Brain genes

• Gay genes? Xq28

• 1,098 genes

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Hemophilia the Royal Family
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X-linked traits
Male Pattern Baldness
Red-green color deficiency
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Jon has male pattern baldness his partner
Michelle is not bald but her father has male
pattern baldness. What is the probability that,
if they have a son, he will be bald? a. 1/8 b.
¼ c. ½ d. ¾
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Single Active X
At 500 to 1000 cell stage in female mammals, one
of Xs in each cell is turned off
Remaining X is called the single active X
Being a random event, approximately half of all
cells will have an active paternal X and half
will have an active maternal X.
Thus, all female mammals are a patchwork of
paternal and maternal traits coded for by the X
chromosome.
If the genotype is homozygous dominant of
recessive, it is of no consequence. However, if
the genotype is heterozygous, ?
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Single active X and calico cats
Orange coat color dominant to black
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The reason for single active X
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VII. Linkage and crossing over
Genes are said to be linked if they are on the
same chromosome
The closer two genes are on a chromosome, the
more tightly linked they are and the more likely
they will be inherited together.
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VIII. Genes and behavior
Twin studies
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Genes for behavior?
Novelty seeking genes and dopamine receptors
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Genes for behavior?
tryptophan
Shyness (harm avoidance) and serotonin
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The end