GHSGT Review

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GHSGT Review

• Biology
• Part 2 Genetics DNA

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What Is Genetics?

• Study of heredity - how genes are passed on from
  1 generation to the next.

• Gregor Mendel -
• father of genetics
• Studied pea plants
• Noticed that certain traits are passed on from
  parents to offspring

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One of Mendels Observations

• Some alleles are dominant others are recessive
• HINT An allele is a different form of a gene.
• For example You may have the brown eye allele
  while your best friend has the blue eye allele

• T tall
• t short

Tall is DOMINANT because it is represented by a
capital letter (T). Short is RECESSIVE since it
is a lowercase letter (t).
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Alleles

• Heres an example of the flower color allele.
  The color of the flower depends on the
  combination of alleles that are inherited.

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TT, Tt and ttWhat Does It All Mean?

• Lets use T to represent height.

TT Tall tt short
Does Tt represent tall or short? Why? Hint
If you see a dominant (capital) letter, then
that will be the trait.
TT
tt
X
Tt
Tt
Tt
Tt
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Important Words

• Phenotype The physical characteristics of an
  organism
• This is what you see.
• Ex Brown hair, blue eyes

• Genotype The genetic makeup of an organism
• You inherit your genotype from your parents, its
  the code in your DNA
• Ex If a flower inherits BB, it will be purple,
  if it inherits bb it will be white.

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Punnett Squares

• Punnett Squares are diagrams that help us to
  predict the outcome of a cross

• B Purple
• b White
• Notice that if a dominant gene is present, you
  will see that color
• What of flowers are purple in this cross?

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How To Do It!
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Lets Practice

• What of the offspring will be purple?
• 75
• What will be white?
• 25

RR Purple rr White
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More Important Words

• Heterozygous An organism that has 2 different
  alleles

• How many organisms are heterozygous in the
  Punnett Square shown above?

TT
Tt
Tt
tt
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More Important Words

• Homozygous When an organism has 2 of the same
  alleles

Homozygous Recessive
Homozygous Dominant
TT
Tt
Tt
tt
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Lets Practice

• What of the offspring are homozogyous?
• What of the offspring are heterozygous?
• What of the offspring are homozygous recessive?

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DNASection 2 of Day 2 Review

• DNA is a nucleic acid
• Heredity molecule
• Determines an organisms genotype and therefore
  its phenotype
• Shape Double helix
• Made of
• Sugar
• Phosphate
• Nitrogen base pairs
• Why do you supposed it is called a double helix?

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DNA Base Pairs

• A very common question is
• DNA contains nitrogen base pairs. What base
  pair does A pair with?
• REMEMBER
• A pairs with T
• C pairs with G

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Where Is DNA Found?

• DNA is found in all living organisms
• Its located in the nucleus of the cell!

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Lets Practice

• Match the appropriate nitrogen base pairs in
  diagram H.
• ANSWER
• G C
• C G
• A T
• T - A

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Lets Practice

• What is the shape of a DNA molecule?
• ANSWER
• Double Helix

How many strands does DNA have?
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Some More Practice

• Where is DNA found in the cell?
• ANSWER
• The Nucleus

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Punnett Square Practice

• In corn plants, green (G) is dominant to albino
  (g). According to the punnett square, what is
  the chance of this heterozygous cross producing
  albino corn plants?

• Multiple Choice ANSWERS
• 1 in 4
• 2 in 4
• 3 in 4
• 4 in 4

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Some More Practice

• In apples, red is dominant (A) to yellow (a).
  What percentage of apples will have the red
  phenotype?
• ANSWER
• 25
• 50
• 75
• 100

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Any Questions?