INTRODUCTION TO GENETICS

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CHAPTER 11

• INTRODUCTION TO GENETICS

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CHAPTER 11.1

• The Science of Inheritance
• Why do children resemble their parents?

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CHAPTER 11.1

• Heredity biological inheritance
• Characteristics an organisms receives from its
  parents
• Study of heredity genetics
• Gregor Mendel
• Lived in mid-1800s Austrian monk scientist
  mathematician

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CHAPTER 11.1

• Worked with pea plants
• Could control pollination
• Had pure bred strains when crossed all
  offspring are identical to parents
• Pea plants had 7 traits each with only 2 forms
• Mendel developed hybrids (offspring of parents
  with different characteristics)

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CHAPTER 11.1
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CHAPTER 11.1

• EXAMPLE
• P pure tall X pure short
• AA aa
• All offspring (F1) all tall
• Traits did not blend all offspring looked like
  one parent only
• Mendel was able to do this for all 7 traits

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CHAPTER 11.1
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CHAPTER 11.1

• Then he crossed F1 X F1 ? F2
• Example hybrid tall X hybrid tall
• ¾ offspring tall
• ¼ offspring short
• The hidden trait came back in F2

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CHAPTER 11.1
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CHAPTER 11.1

• So. Sometimes offspring characteristics are
  quite different from parent

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CHAPTER 11.1

• GENETICS VOCABULARY
• Gene unit of DNA (section of DNA) that
  determines a trait
• Alleles different forms of a gene for the same
  trait
• Example the gene for tall is an allele to the
  gene for short but not an allele to the gene for
  white flowers

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CHAPTER 11.1

• Each cell has a pair of alleles for each trait
• A gamete has just one allele of a pair (two
  gametes combine ? pair)
• Dominant allele the dominant trait is seen if
  one or both dominant alleles make up the pair
• Recessive allele the recessive trait only shows
  if BOTH recessive alleles make up the pair

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CHAPTER 11.1

• Use the capital letter of the dominant form
  dominant allele, use the lower case letter of
  dominant form recessive allele
• Tall T short t pure tall TT pure short
  tt hybrid tall Tt

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CHAPTER 11.1

• Phenotype descriptive word for a trait how
  something looks or appears
• Tall, short, white, purple, round, wrinkled, red
• Genotype letters used to stand for the gene
  pair
• TT, Tt, tt, GG, Gg, gg, AA, aa, Aa, MM, Mm, mm
• Homozygous both genes for a trait are the same
• TT, tt, GG, gg, AA, aa, MM, mm

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CHAPTER 11.1

• Homozygous both genes for a trait are the same
• TT, tt, GG, gg, AA, aa, MM, mm
• angel fish homozgyous for marble (MM)

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CHAPTER 11.1

• Heterozygous the gene pair includes one
  dominant allele and one recessive allele
• Tt, Rr, Ss, Mm, Nn, Aa
• Angel fish heterozygous for marble (Mm)

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CHAPTER 11.1

• When describing the dominant phenotype, you must
  say homozygous tall if it is TT or heterozygous
  tall if it is Tt. You do not have to use the
  word homozygous in front of short (the recessive
  phenotype) because it must always be homozygous
  if it is the recessive form.

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CHAPTER 11.1

• PUNNETT SQUARES
• Definition a mathematical way to figure the
  expected outcome of a cross
• The actual numbers could be lower if the number
  of offspring is low

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CHAPTER 11.1

• Steps in monohybrid cross (looking at only one
  trait at a time)
• Write out the genotypes of the parents in the
  cross
• TT X tt

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CHAPTER 11.1

• In the formation of gametes (sex cells), the gene
  pair separates each gamete has only one gene of
  a pair
• Determine the possible gametes that could be made
  by each parent
• TT could only have gametes that contain T
• Tt could have two different gametes one with
  T and one with t
• tt could only have gametes that contain t

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CHAPTER 11.1

• Draw the Punnett square fill in the gametes
  one parent across the top and one down the side

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CHAPTER 11.1

• Fill in Punnett square by looking up over (
  illustrates the gamete fertilization
  possibilities)

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CHAPTER 11.1

• List offspring genotypes ratios
• AA 25
• Aa 50
• aa 25
• Or 1 AA 2 Aa 1 aa

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CHAPTER 11.1

• List the offspring phenotypes ratio
• SS Ss both produce the dominant phenotype 75
  round pea seeds
• ss produces the recessive phenotype 25
  wrinkled pea seeds
• Round 75 wrinkled 25
• Or 3 round 1 wrinkled

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CHAPTER 11.1

• On the bottom of your page you cross two
  heterozygous tall pea plants.

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CHAPTER 11.1

• ANSWER Tt X Tt
• Genotype TT 25
• Tt 50
• tt 25
• Phenotype
• tall 75
• short 25