Genetics

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Genetics

• TEKS 6F Predict possible outcomes of various
  genetic combinations such as monohybrid crosses,
  dihybrid crosses, and non-Mendelian inheritance.

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Gregor MendelFather of Modern Genetics

• Performed experiments with pea plants
• Helped determined how traits are passed from one
  generation to the next.

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How are offspring influenced by genetic
combinations?

• Parents pass on units of information called
  genes.
• These genes produce traits, which are
  characteristics that make up an organism. Ex
  height, hair color, blood type, intelligence.
• For each trait, an individual has two alleles
  (different forms of a gene). Alleles are
  represented as letters (ex TT can stand for the
  trait of tallness). How are these passed along?

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Where she get that booty from?She get it from
her mommaand her daddy

• Traits are passed on from parents.
• You inherit ½ of your genes from your mom and the
  other ½ from your dad.
• These come from the sperm and the egg when an egg
  is fertilized.

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Mendels principle of dominance
FAQs

• Mendels principle of dominance states that some
  alleles are dominant and others are recessive.
• Dominant alleles are written with capital letters
  (ex TT, Tt)
• Recessive alleles are always written in lower
  case letters (ex tt)
• The recessive allele is exhibited only when the
  dominant allele is not present.

• How do I know if its dominant?
• If there is even one big letter, it is dominant.
  (TT and Tt)
• Why is Tt dominant if it has a small letter?
• Because there is a big letter next to it.
  Dominant will always overpower recessive!
• How do I know if its recessive?
• If it has two little letters, it is recessive.
  (tt)

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Homozygous vs. Heterozygous
FAQs

• When both alleles (letters) are the same, the
  individual is homozygous for that trait. This is
  also called true-breeding.
• When the alleles are different, the individual is
  heterozygous for the trait. This is also called
  hybrid.

• What if the letters are both big, like SS or TT?
• It is Homozygous.
• What if the letters are both little, like ss or
  tt?
• It is Homozygous.
• What if one letter is big and one letter is
  little, like Ss or Tt?
• It is Heterozygous because they are different
  sizes.

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Genotype vs. Phenotype
FAQs

• The genetic makeup of an organism is called its
  genotype. Write this as letters, like TT.
• The organism's physical traits are its phenotype.
  Write this as a description, like tall, red..

• Is Aa a genotype or phenotype?
• Genotype! Because its just the letters.
• Are purple, tall, short, white, and round
  genotypes or phenotypes?
• Phenotypes! Because its a physical description.
• What is an organisms genotype if it receives two
  recessive alleles for height (Ttall, tshort)?
• tt. Because little letters are recessive. The
  phenotype would be short.

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How can you predict which traits will be
expressed using monohybrid crosses?

• When doing a genetic cross, the parent organisms
  are the P, or parental generation.
• The offspring are called the F1, or first filial
  generation.
• A monohybrid cross is a cross in which there are
  two contrasting alleles for a single trait.
• A Punnett square is a diagram that helps predict
  combinations in genetic crosses. Punnett squares
  are easy to construct.

• Do this animation http//www.siskiyous.edu/class/
  bio1/genetics/monohybrid_v2.html
• You can watch this for more practice and
  explanation http//biology-animations.blogspot.co
  m/2011/07/punnett-square-animation.html

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Practice with monohybrid crosses on the
whiteboard!
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What if you are using more than one trait, like
someone that has blue eyes and is short?

• You would use a dihybrid cross instead of a
  monohybrid cross.
• A dihybrid cross is a cross that shows the
  possible offspring for two traits.

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How do you predict the outcomes of dihybrid
crosses?

• Lets do an example!

Coat Texture R Rough r Smooth
Fur Color B Black b White
In this example, we will cross A heterozygous
black/heterozygous rough individual with another
heterozygous black/heterozygous rough individual.
Their genotypes will be __________.
BbRr x BbRr
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How do you predict the outcomes of dihybrid
crosses?
BR, Br bR, br
BR, Br bR, br

• BbRr x BbRr
• First, you must find ALL possible gametes that
  can be made from each parent.
• Remember, each gamete must have one B and one R.

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How do you predict the outcomes of dihybrid
crosses?

• BbRr x BbRr
• Possible gametes
• BR
• Br
• bR
• br

Next, arrange all possible gametes for one parent
along the top of your Punnett Square, and all
possible gametes for the other parent down the
side of your Punnett Square
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How do you predict the outcomes of dihybrid
crosses?
BbRr x BbRr
Fur Color B Black b White
Coat Texture R Rough r Smooth
Then, find the possible genotypes of the offspring
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How do you predict the outcomes of dihybrid
crosses?
BR
Br
bR
br
BbRr x BbRr
BR
BBRR
BbRR
BbRr
BBRr
Fur Color B Black b White
Br
BBRr
BBrr
BbRr
Bbrr
Coat Texture R Rough r Smooth
bR
BbRR
BbRr
bbRR
bbRr
br
BbRr
Bbrr
bbRr
bbrr
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How do you predict the outcomes of dihybrid
crosses?
BR
Br
bR
br
How many of the offspring would have a black,
rough coat? How many of the offspring would have
a black, smooth coat? How many of the offspring
would have a white, rough coat? How many of the
offspring would have a white, smooth coat?
BR
BBRR
BbRR
BbRr
BBRr
Br
BBRr
BBrr
BbRr
Bbrr
bR
BbRR
BbRr
bbRR
bbRr
br
BbRr
Bbrr
bbRr
bbrr
Fur Color B Black b White
Coat Texture R Rough r Smooth
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How do you predict the outcomes of dihybrid
crosses?
How many of the offspring would have black, rough
coat? How many of the offspring would have a
black, smooth coat? How many of the offspring
would have a white, rough coat? How many of the
offspring would have a white, smooth coat?
Phenotypic Ratio 9331
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More dihybrid practice..

• In pea plants, yellow seeds (Y) are dominant over
  green seeds (y), and rounded peas (R) are
  dominant over wrinkled peas (r).
• Cross a plant that is heterozygous for both
  traits with a plant that is homozygous recessive
  for both traits. Draw a Punnett square to show
  all possible offspring, and determine the
  genotypic and phenotypic ratios.

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YyRr X yyrr
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Non-mendelian genetics What are some other
patterns of inheritance?
Some forms of inheritance are distinctly
non-Mendelian inheritance because they do not
follow the principles described by Gregor
Mendel. Incomplete Dominance and Codominance
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Incomplete Dominance

• Neither allele is dominant, so the traits blend
  together.
• Phenotypes combine to create a separate trait.
• Example, red and white snapdragons offspring
  pink snapdragons

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Incomplete Dominance

• You can use two different letters now!
• RR (red) X WW (white)

R R
W RW pink RW pink
W RW pink RW pink
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Incomplete Dominance Practice

• Cross of two purple flowers (what 2 colors make
  purple?)____ X ____
• What are the genotype ratios?
• 1RR 2RB 1BB
• What are the phenotype ratios?
• 1red 2 purple 1 blue
• Can you have a heterozygous red orhybrid blue
  flower? ___

RB
RB
R
B


RR
RB
R
red
purple
BB
RB
B
purple
blue
no
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Codominance

• Expression of both alleles equally
• Phenotype of both traits are seen in heterozygous
  individuals
• Example black rooster and white chicken produce
  offspring with both black and white feathers.

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Punnett Square of Codominant cross

• Expressed as two separate traits in a Punnett
  Square Cross
• BB (black) X WW (white)

B B
W BW (Black and white) BW (Black and white)
W BW (Black and white) BW (Black and white)