Heredity and Genetics

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Heredity and Genetics
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Just think

• My parents have brown eyes, why are mine blue?
• My brother is tall. Why am I short?
• Why does my sister have blonde hair while mine
  is brown?

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Science can answer some of these questions

• Heredity- the passing of characters from parents
  to offspring
• Genetics- the branch of biology that focuses on
  heredity

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Gregor Mendel
Father of Genetics
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During his early years at the monastery, Mendel
began studying and breeding mice.
The bishop was not pleased.
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Brother Gregor settled on bees . . .
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and peas.
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Why Peas?

• The garden pea is a good subject for several
  reasons. Peas
• Have traits that are inherited by simple
  dominance, one trait is dominant to another, ie.
  Tall is dominant to short in peas
• Have male and female reproductive parts enclosed
  on the same structure - mating can be controlled
  and done with the bristles of a brush
• Are small, grow easily, mature quickly, and
  produce many offspring (results can be quickly
  obtained and there are plenty of subjects to
  count)

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Mendelian Theory of Heredity(the foundation of
genetics)

• For each inherited character, an individual has
  two copies - one from mom and one from dad

• There are different
• versions of genes alleles

For example, the gene for pea seed color can be
green or yellow. What are different alleles for
eye color?
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Mendelian Theory of Heredity(the foundation of
genetics)

• 3. When two different alleles (versions) occur
  together, one of them may be completely
  expressed, while the other may have no observable
  effect on the organisms appearance.

Dominant- the expressed form of the trait
Ex. E
Recessive- the trait that is not expressed if a
dominant allele is present
Ex. e
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Mendelian Theory of Heredity(the foundation of
genetics)

• When gametes are formed (in what process?)
  alleles for each gene separate - gametes only
  carry one allele for each characteristic
• During fertilization,
• gametes unite - each
• gamete contributes one
• allele to the offspring.

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Modern Terms

• Genotype- the genetic makeup of an organism (the
  set of alleles an individual has)

Ex. EE, Ee, ee
Phenotype- the physical appearance of an
organism
Ex. Purple, tall, round
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Modern Terms

• Homozygous- the two alleles present for a
  character are the same
• ex. EE or ee
• Heterozygous- the two alleles present for a
  character are different
• ex. Ee

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Labeling the Generations

• P generation parent generation
• F1 Generation first filial, offspring of the P
  generation
• F2 generation second filial, offspring of the
  F1 generation

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Predicting Heredity
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Probability

• The likelihood that a specific event will occur

First Law Each trial of a chance event is
independent of all other trials of the same
change event. Application What is the chance
that you will roll a 1 the first time you roll a
dice? What is the chance that you will roll
a 1 the second time you roll a dice?
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• Second Law (also called Law of Muliplication)
  The chance of independent events occurring
  together is the product of the chances for each
  independent event occurring separately.
• Application Two people have a coin. They are
  tossing the coins at the same time. What is the
  chance that both will come up heads?
• What is the chance that both will come up tails?

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Probability

• What is the probability that a couple will have
  four boys in a row?

1/2
1/2
1/2
1/2
½ x ½ x ½ x ½ 1/16
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• Problem If one out of two students is female
  and one out of eight students is left handed and
  one out of 12 is red haired, what is the
  probability that the next person you will see
  will be left-handed, red-haired girl?

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• Third Law (also called Law of Addition) The
  probability of an event that can occur in two or
  more different ways is the sum of the separate
  possibilities of those ways.
• Application Two people have a coin. They are
  tossing the coins at the same time.
• What is chance that one will come up heads and
  the other come up tails?

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Now, lets see if this works in the real world

• Each student will flip a penny 10 times and
  record the results. Based on probability, how
  many heads should there be? Tails?
• Your results
• Heads_______
• Tails ________
• Class results
• Heads _______
• Tails ________
• Which results are closest to your prediction
  based on probability? Yours or the classes?

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Each student needs a penny and a partner!

• Each student with their partner each flip their
  penny. Record the results whether it be 2 heads,
  2 tails or 1 heads and 1 tails. Do this 20
  times.
• What is the predicted result based on
  probability?
• Your results HH_____ HT _____ TT_____
• Class results HH _____ HT _____ TT______
• Which are closer to the predicted results?
• Yours or the classes? Why?

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• a. Miguel has just received an IPOD as a gift.
  He has downloaded 3 country music songs,1 rhythm
  and blues song, 5 rap songs, and 1 song that is
  the theme song to his favorite movie. If the
  IPOD is set on playing these songs at random,
  what is the probability that he will hear a
  country music song?

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• b. Sherri has a pocket full of colored candy
  jelly beans. She has 6 pink jelly beans, 3
  yellow jelly beans, 10 green jelly beans, and 1
  orange jelly bean. What is the probability that
  Sherri will select a green jelly bean and then,
  without replacing it, randomly select an orange
  jelly bean from her pocket?

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Monohybrid Crossa cross that shows the possible
offspring for one trait
Example Cross two heterozygote individuals Aa
x Aa
A White fur a Brown fur
Genotypic Ratio 121
Phenotype 3 white1 brown
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Practice!
Cross a HOMOZYGOUS dominant with a HOMOZYGOUS
recessive using the same trait.
What is the genotypic ratio?
Aa
Aa
4/4 which gives 1
What is the phenotypic ratio?
Aa
Aa
4/4 which is 1 or 100 white fur
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Practice!
Cross a HOMOZYGOUS dominant with a HETEROZYGOUS
using the same trait.
What is the genotypic ratio?
AA
AA
22 which reduces to 11
What is the phenotypic ratio?
Aa
Aa
4/4 white fur, which reduces to 1 or 100
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Test Cross

• Animal breeders and horticulturists often need to
  know if an organism is homozygous dominant or
  heterozygous for a character. However, it is
  impossible to tell simply by looking at an
  organism.

They can use a test cross
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Test Cross

• An individual whose phenotype is dominant, but
  whose genotype is not know, is crossed with a
  homozygous recessive individual.
• (Based on the outcome of the cross, you can tell
  if the individual in question is homozygous
  dominant (TT) or heterozygous (Tt).)

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Test Cross

• Is this purple flowering pea plant PP or Pp?

Cross the unknown with a homozygous recessive
individual.
P? X pp
Set up a Punnett squares
P
p
P
P
Pp
pp
Pp
Pp
Pp
pp
Pp
Pp
Based on the actual outcome of the cross,
determine the genotype of the unknown.
(If all offspring are purple, the unknown must
have been PP)
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Test Cross

• Consider that tallness in pea plants is dominant
  to dwarfism. A horticulturalist has a tall
  plant, however is unaware of its genotype. She
  has a contract to produce all tall plants. Show
  the test cross she will have to make in order to
  be sure that the tall plant she uses to make
  offspring is a purebreeding tall plant. What are
  the possibilities with a tall plant?
• The tall plant could be either TT or Tt. So you
  cross it will a tt.