Download File - Siegel Science

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Farmers realized thousands of years ago that if
you only breed parent plants & animals that have
the best characteristics you could produced
offspring that also had those favorable
characteristics.
This practice is referred to as selective
breeding…sound familiar?
Selective breeding practices have led to the
production of thousands of varieties of potatoes
that differ in size, color, and how long they can
be stored.
 the
study of inheritance or heredity;
the process by which characteristics
or traits are passed down from parent
to offspring
Challenge: What can
we infer about genes
and traits based on
heredity patterns?
What we know & understand
about inheritance is based on
the work of Gregor Mendel
and his experiments with pea
plants. He performed
controlled experiments and
kept detailed records.
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1860’s
Austrian monk with a
background in biology,
math & physics
Used pea plants to
make lots (I mean
LOTS!) of observations
and predictions about
heredity
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1843 – Mendel, at age 21, entered a
monastery in Austria in order to study to
become a teacher; he flunked the teacher
exam... 
1851 – Was sent to the University of Vienna to
work on his studies; he came to enjoy
studying science and math; tried to take the
teacher exam again & failed... 
Few years later - he returned to the Austrian
monastery; used his knowledge of science &
math to study biological patterns &
occurrences in nature… 
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Mendel chose pea plants
because they were easy to
grow & had 7 different,
easily observable, traits .
Each trait has only 2
distinct forms – no in
betweens.
What do we call “in
betweens”??????? (Think
pink rose from red &
white roses…)
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First time, he crossed a pure-bred tall plant (What
does pure-bred mean?) with a pure-bred short
plant.
Genotypes of these
plants?
He ended up with
all tall plants in this
F1 generation.
What is F1 you ask?
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Mendel allowed the hybrid
(what is this?) to self-fertilize.
So what will these genotypes
look like?
He ended up with 3 tall plants
for every 1 short plant
produced in the F2 generation.
Gee, where have you seen this
ratio before?
Mendel repeated this with
multiple other traits and guess
what?
You got it, he got the same
ratio every time!!!
Mendel’s Data:
Characteristic Dominant
Recessive
Ratio (Dom:Rec)
Flower Color
Purple
White
705: 224  3.15:1
3:1
Seed Color
Yellow
Green
6,022: 2,001  3.01:1
3:1
Seed Surface
Smooth
Wrinkled
5,474: 1,850  2.96:1
3:1
Pod Color
Green
Yellow
428: 152  2.82:1
3:1
WHAT IS UP WITH THIS 3:1
Ratio?!?!?!
1) A dominant trait, if present, will
always appear in the individual. The
trait that seems to be “hidden” is the
recessive trait.
2) Every plant has 2 versions, alleles, of
the gene for each trait.
3) Every offspring receives 1 allele for
each trait from each parent.
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Traits are characteristics
that can be passed on
from parents to offspring
(e.g. hair & eye color) and
are controlled by GENES.
Each gene has different
forms or versions called
alleles.
(e.g. trait=eye color,
alleles=brown & blue)
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Involves 2 parents
Each parent produces gametes
◦ Males produce sperm
◦ Females produce eggs
Each gamete carries 1 allele for each gene
Fertilization=1 sperm cell fuses with 1 egg
cell to produce a zygote
Offspring that develops from that zygote has
a unique combination of genes passed to
them from both parents
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Purple corn kernels are
dominant over yellow
corn kernels
What is the genotype of
corn w/purple kernels?
PP or Pp
What is the genotype of
corn w/yellow kernels?
ff
If the genotype is Ff it is
referred to as…
Heterozygous
If both alleles are the
same?
homozygous
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Cross – breeding combination; TT x Tt
Parent generation (P) - the two plants selected
to cross for a breeding experiment
First Filial generation (F1) - all the offspring
produced by crossing the two (P) individuals.
Second Filial generation (F2) - all the offspring
produced by crossing two of the F1 individuals.
True Breeding or Purebred- refers to a plant
that passes on the same trait from one
generation to the next. (HmD or HmR)
Hybrid – refers to a plant that passes on
different traits from one generation to the next.
(Ht)
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Incomplete dominance=
when neither allele is
dominant
Heterozygous individuals
show a phenotype in
between the other two
Example: hair texture in
humans
Curly hair=HH
Straight hair=hh
Wavy hair=Hh
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Codominance=more than one allele is dominant,
both are expressed equally
Ex. blood types in humans
There are actually 3 alleles for the blood type trait
in humans (A, B, and O)
If a child has type O blood, what blood types
might his or her parents have?
Some traits are polygenic, meaning that
the phenotype of the individual is
determined by several genes.
 Ex. Eye color and Hair color
 Many traits are determined not just by
the genes you inherit, but also
environmental conditions
 Ex. skin pigmentation
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1. Explain the difference
between an organism’s
phenotype and its
genotype. Include an
example in your
answer.
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An organism’s
genotype refers to the
actual alleles that the
organism inherits for
the gene.
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An organism’s
phenotype refers to the
physical appearance of
Genotype: TT or Tt
Phenotype: regular thumb
Genotype: tt
Phenotype: Hitchhiker’s
thumb
2. Explain the difference between simple
dominance, incomplete dominance, and
codominance.
 Simple dominance refers to one allele being
completely dominant over another. Example: in
pea plants purple is dominant over white for
flower color; as long as the purple allele is
present it will be expressed
 Incomplete Dominance means that neither allele
is dominant over the other
 Codominance refers to both alleles are dominant
and are both expressed
3. Think back to the Bt corn you considered in
Activity 1. When an organism is genetically
modified, which of the following is changed:
genotype, phenotype, both or neither? Explain.
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When an organism is genetically modified its
genes are being changed so that means that the
genotype would be altered. If the genotype is
altered then the phenotype would also be altered.
The phenotype is determined by the genotype.
AQ #4-What type of inheritance is being exhibited
by each example?
codominance
Simple dominance
Incomplete dominance