Transcript Chapter 12 - Cloudfront.net

Chapter 12
Patterns of Heredity
and Human Genetics
Chapter 12.1 Scientific Terms
1.
2.
3.
Pedigree
Carrier
Fetus
1. What is a pedigree? How do you make
one?
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Pedigree  graphic representation of
genetic inheritance
- looks like a “family tree”
It is made of a set of symbols that
identify:
- male or female
- the trait being studied
- the relationships between the members 
2. Describe how you would analyze a
pedigree. Why are these useful?
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Pedigrees show “carriers”, which are
heterozygous individuals
You can follow a trait through generations
by looking at a pedigree
Helpful for knowing the possibility of
genetic disorders, or any recessive trait 
3. Describe what “simple recessive heredity”
refers to. Describe the three recessive
disorders that the book discusses.
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1.
2.
3.
Genetic disorders caused by a homozygous
recessive situation (rr or tt, etc)
Cystic fibrosis  1 in 28 white Americans carry
the recessive allele (Rr)
- 1 in 2500 white kids born with it
Tay-Sachs  common in Amish people and
Jewish people from eastern Europe
Phenylketonuria  common in descendants of
Norway and Sweden 
4. Describe what “simple dominant heredity”
refers to. Overview the several dominant
traits that the book discusses.
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A trait is inherited with at least one dominant
allele (RR or Rr)
Tongue rolling
Free hanging ear lobes
Hitchhiker’s thumb
Almond shaped eyes
Full lips
Hair on middle section of fingers
Huntington’s disease 
Section Assessment

Answer questions (1-4) on page 314.
Chapter 12.2 Scientific Terms
1.
2.
3.
4.
5.
Incomplete dominance
Codominant allele
Multiple allele
Autosome
Sex chromosome
5. Describe the concept of “incomplete
dominance” and describe an example.
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When the phenotype of the heterozygote
is a blending of the two homozygotes
Ex: If a red flower (RR) is crossed with a
white flower (R’R’), the resulting offspring
are heterozygotes (RR’) which look pink 
6. Describe the concept of
codominance. Show an example.
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Codominant alleles cause the phenotypes of
both homozygotes to be produced in the
heterozygote
Both alleles are expressed equally, not
combined
When a black chicken is crossed with a
white chicken, the offspring are NOT gray,
they are black and white 
7. Describe the concept of multiple
phenotypes from multiple alleles.
Describe the book’s example.
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It is common for more than 2 alleles to
control one trait
Traits controlled by more than 2 alleles
have “multiple alleles”
In pigeons, a single gene that controls
feather color has 3 alleles
Ex: BA makes red feathers
B makes blue feathers
b makes chocolate colored feathers 
8. What is the difference between autosomes and
sex chromosomes? How do the sex chromosomes
affect sex-linked inheritance? Can you think of any
sex-linked traits in humans?
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Autosomes  the 22 pairs of homologous
chromosomes besides the sex chromosomes
Sex chromosomes  the 2 chromosomes that
determine the sex of an individual
Sex-linked traits  traits controlled by genes
located on the sex chromosomes
- the Y chromosome has no corresponding allele to
some traits on the X chromosome
Ex: color blindness, male pattern baldness 
Review… write answers with SAQs
1. A blue fish and a yellow fish have all green babies! What
inheritance pattern does fish color follow?
2. A red cow and a white cow have red & white calves.
What inheritance pattern does this follow?
3. What is a chart of chromosomes called?
4. What is II-2’s genotype? 
5. What is most likely II-1’s 
genotype?
Types of Inheritance…
1.
2.
3.
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Complete dominance
Incomplete dominance
Codominance
Multiple Alleles
Sex Determination
Sex-linked inheritance
Polygenic inheritance
Environmental Influences
Chapter 12.2 & 3 Terms
1.
2.
3.
Sex-linked trait
Polygenic inheritance
Karyotype
*Turn in terms
sheet*
9. Describe what polygenic inheritance
is and describe an example.
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It is the inheritance pattern of a trait
that is controlled by two or more genes
Ex: skin color (AABBCC)
- the CAPITAL letters are darkness
- the lowercase letters are lightness
AABBCC AaBbCc
aabbcc AAbbCc
very dark
medium
very light
medium 
10. How does the environment influence
genetic expression? Describe the influence
of the external and internal environments.
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The genetic makeup at fertilization is the
potential
Many factors can influence how the gene is
expressed (internal and external factors)
External  temperature, nutrition, light,
chemicals, infections
- Ex: tree leaves, height
Internal  male vs female due to hormones and
structural differences
- Ex: horn size, male baldness, peacock feathers 
11. Describe what disorder exhibits
codominance in humans, and why this is
actually an advantage.
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Sickle-cell anemia
Most common in African-Americans and white
Americans from the Mediterranean
About 1 in 12 are heterozygous (RR’) and
produce both normal RBCs and sickle ones
Advantage in malaria 
12. Describe how multiple alleles govern
human blood types, and why this is
important to know.
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ABO blood group
Determined by the presence or absence of
surface proteins on RBCs
Three alleles for the “I” trait  IA, IB, i 
Section Assessment

Answer questions (1-4) on page 322
Turn in your
Ch 12.2 sheet
Types of Inheritance…
1.
2.
3.
4.
5.
6.
7.
8.
Complete dominance
Incomplete dominance
Codominance
Multiple Alleles
Sex Determination
Sex-linked inheritance
Polygenic inheritance
Environmental Influences
13. Describe the two sex-linked traits
talked about in your book. Why do
males usually get these disorders?
1.
2.
Red-Green color blindness
- caused by two recessive alleles at two gene
sites on the X chromosome
Hemophilia
- problem with blood clotting
- 1 in 10,000 males
- 1 in 100,000,000 females
- inherited on X chromosome from mother
carriers
- treated with blood transfusions and Factor
VIII (a blood clotting enzyme) 
14. Describe how skin color is
considered polygenic inheritance.
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There aren’t just light and
dark people, there are
intermediates also
Ex:
light person + dark person
= medium people
medium + medium = dark,
medium, light
The “AABBCC” idea from
before 
15. What happens when there are
changes in the chromosome numbers in
humans?
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Many abnormal phenotypes result from
changes in chromosome numbers
Missing information
Too much information
Usually results in disorders 
16. How do scientists figure out if
someone has an unusual number of
autosomes?
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Normal: 23 pairs (46 chromosomes)
22 pair are autosomes; 1 pair are sex
If unusual autosome number, can have 47
or more chromosomes
A “karyotype” is a chart of chromosome
pairs from an individual’s cells 
17. What happens when an individual has
an extra chromosome 21?
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Usually disorders of chromosome number
cause problems so severe the fetus dies
Down syndrome  the only autosomal
trisomy where the individual survives into
adulthood (1 in 700 births)
It is a trisomy of chromosome 21
Higher incidence in mothers over 40 years
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18. Describe the abnormalities that occur
when there is an unusual number of sex
chromosomes.
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The 2 sex chromosomes
XX if female and XY if male
An X chromosome can be missing and be
XO
An X may be extra and be XXY or XXX
An extra Y could be added and have XYY
There is not enough information in the Y to
have no X at all  YO won’t happen 
MiniQuiz
Which inheritance pattern is exhibited by the
following:
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Red flowers + white flowers = pink flowers
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Red, blue, and chocolate pigeon feathers
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Black chicken + white chicken = checkered
chicken
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Red-green colorblindness & hemophilia
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Cystic fibrosis & Tay-Sachs disease
Section assessment
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Answer questions (1-4) on page 329
The End!