CHARACTERISTICS OF LIFE

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CHARACTERISTICS OF LIFE
All Living Things reproduce!!!
All Living Things Have DNA!!!
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WHY ARE WE ALL DIFFERENT?
We all inherited different genes from our parents
which determines our traits.
Heredity Passing on of genes which determine
your traits from parents to offspring.
23 chromosomes from each parent.
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Genes Pieces of DNA that carry
hereditary instructions and are passed from
parents.
Traits A distinguishing characteristic that is
passed from parents to offspring.
Genetics Study of heredity (passing on of genes)
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Johann Gregor Mendel was born July 22, 1822.
Mendel became a friar at the Augustinian
monastery in Brno, Czechoslovakia. From 1868
until his death, Mendel was the abbot of the
monastery. Mendel was experimenting with
flowers in the monastery's gardens. He wondered
how traits were passed from parent to offspring.
He studied the relations between parents and
offspring with mathematical symbols. His favorite
plants to experiment with were peas. FATHER Of
genetics
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MENDELS EXPERIMENT
PART 1 He bred a tall pea plant with a pure short
pea plant. But ALL the offspring were TALL.
How could that be? Maybe a mistake was made?
PART 2 He crossed 2 of the offspring from the
above cross. Results 75 Tall 25
Short Now wait a minute!! He crossed two tall and
go a short? Whats going on?????
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GENETIC RULES
Every organism has TWO forms of a gene for each
trait. One from each parent. Each form is called
an ALLELE.
You can receive a dominant or recessive gene
From your parent.
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GREGOR MENDEL
He realized in the first cross, one trait
appeared and the other seemed to be masked.
The trait that masks or is stronger than the
other trait is called the dominant trait. The
trait that is covered up is called the recessive
trait.
For these reasons, Mendel is called the Father
of Genetics.
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GENETICS RULES and SYMBOLS
Scientists use symbols to represent different
forms of a gene.
Capital Letters Represents dominant trait.
Dominant traits are the stronger traits.
Lower Case Letters Represents recessive trait.
Recessive traits are the weaker traits that are
often masked by dominant traits.
Examples-BB brown eyes bb - blue Bb brown
eyes
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Example Dominant Traits
Brown Eyes- B Widows Peak- W Unattached
Earlobes- E Freckles- F
Example Recessive Traits
Blue eyes- b Straight hairline- w Attached
earlobes- e No Freckles- f
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Homozygous vs. Heterzygous
If the inherited genes (alleles) are the same,
then they are called HOMOZYGOUS or purebred.
Letters are the same size.
Examples aa , AA , LL , ll , TT , tt
If the inherited genes are different, then they
are called HETEROZYGOUS or hybrid. Letters are
different sizes.
Examples Aa , Ll , Tt, Bb
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Genotype vs. Phenotype
The genotype is the letter combination or gene
combinations Example Tt, Aa, bb,or Ll
The phenotype is the actual appearance of the
organism. Example tall, brown hair, blue eyes,
long toes
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GENETIC PROBABILITY
Mendal crossed yellow and green pea plants and
discovered that 1 out of 4 were green.

He was using probability.
Probability The possibility or likelihood
that a particular event will occur.
Used to predict the results of genetics crosses.
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PUNNETT SQUARES
A Punnett square is a special chart used to show
the possible gene combinations in a cross
between 2 organisms. (also called monohybrid
crosses)
Developed by an English geneticist by the name
of Reginald Punnett.
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PARTS OF A PUNNETT SQUARE
Male Genes
Female Genes
Offspring Combinations
T tongue roll t cannot roll tongue
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How does a Punnett Square Work?

• Draw a square and divide
• it into 4 sections.
• Write the gene pairs across the top of the box,
  then the
• other down the side.
• In each box, place the correct gene to see the
  possible combinations.

Each square represents a 25 possibility of
getting that trait.
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Cross between homozygous dominant curly tail
(TT) and a homozygous recessive straight tail
(tt).
Tt
Tt
Tt
Tt
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Tt
Tt
Tt
Tt
What are the percentages of the offspring? What
are the genotypes? What are the phenotypes?
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Cross between two heterozygous curly tailed
parents (Tt).
TT
Tt
tt
Tt
What are the percentages of offspring? What are
the genotypes? What are the phenotypes?
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Mathematical Computations
In a Punnett Square where both parents are
hybrids the percents are listed below 25
purebred (homozygous) curly TT
50 hybrid (heterozygous) curly - Tt
25 purebred (homozygous) straight - tt
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of same genotype as parents -
of same phenotype as parents -
75
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Dihybrid Crosses
T- height S-shape T-tall t-short S-square s-ro
und
A dihybrid cross is a cross of two different
traits
Mom T t
S
s
Dad T t
S
s
List of gamete genotypes Mom- Dad-
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Dihybrid crosses- formation of zygote
Mom- ST, St, sT, st Dad- ST, St, sT, st When
parent gametes (egg/sperm) join to form a zygote,
the possible offspring gene combinations are as
follows
Formation of zygote ST (sperm) St (sperm) sT (sperm) st (sperm)
ST (egg)
St (egg)
sT (egg)
st (egg)
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Dihybrid Crosses

• Parent generation gene pairs given by parents.
• Gametes half of parent gene pair
• 1st Generation combination of gametes to produce
  offspring.
• 2nd Generation possible combination of offspring
  from 1st generation cross
• The possible gene combinations from 1st
  generation offspring

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Practice

• G-eye size
• G-large
• g-small
• B- eyebrows
• B-separated
• b-attached

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The squares contain the gene combinations that
could occur in the cross.
The genotype is the letter combination or gene
combinations in the squares. Example Tt, Aa,
bb,or Ll
The phenotype is the actual appearance of the
organism. Example tall, brown hair, blue eyes,
long toes
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INCOMPLETE DOMINANCE
Sometimes, you may notice that traits can blend
together. Two capital letters are used. For
example Red White are equally dominant
producing Pink flowers. Examples roan color in
horses and cows, pink color in flowers are red
and white combined.
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Codominance

• When both alleles contribute to the phenotype.
• For example Chickens- black white feathers are
  codominant, therefore they can appear speckled.

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