Mendelian Genetics

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Mendelian Genetics

• Chapter 11 CP Biology

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• Genetics The scientific study of heredity
• Heredity the passing of traits from parents to
  offspring

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Terms cont.

• Trait any characteristic that is genetically
  inherited
• Dominant trait that masks the recessive form of
  the trait
• Purple dominant to white
• Recessive trait that is masked by the dominant
  form
• Allele each form of a gene for a certain trait
  (P or p)
• Gene sequence of DNA that determines a trait

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• Phenotype- this is a physical trait that you see
• For each trait dominant and recessive
• Thumb type
• Dominant normal
• Recessive - hitchhikers
• Tongue rolling trait
• Dominant rolling
• Recessive non-rolling

Phenotypes
Hitchhikers Thumb
Normal Thumb
Tongue Roller
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• Genotype- This is the two letter code for the
  physical trait.
• The letters each stand for an allele. Each
  allele is found on a homologous chromosome.
• (humans have 23 homologous pairs one allele on
  each of the pairs)
• Half of who you are comes from your mother and
  half from your father.

• A Genotype
• Hh
• A 2 allele letter code

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• Allele- These are the forms of the genes that are
  present represented by a letter.
• Example alleles
• H- no hitchhikers thumb
• h- hitchhikers thumb
• Example genotypes for a hitchhikers thumb
• HH homozygous dominant (has two dominant
  alleles)
• Hh heterozygous (has one dominant allele)
• hh homozygous recessive (has no dominant
  alleles)

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The Origins of Genetics

• Gregor Mendel (1822-1884)
• Father of Genetics
• Monk/Scientist
• Cross pollinated pea plants to see the outcomes
• Noticed atypical characteristics

Gregor's life story
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Mendels Experiments
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• Generation 1
• Purple x White Purple (no
  white)
• (P1 Parents) (F1 offspring)

What does this mean?
Next, he mixed F1 plants with other F1 plants,
and the results were
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• Generation 2
• F1 x F1 Mostly purple, some white
• (P2 Parents) (F2)

Must be some hidden factor that can reappear
Thats a 31 RATIO!
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Phenotype vs. Genotypes

• Trait pea flower color purple is dominant
  white is recessive
• Alleles Purple (P) and white (p)
• Genotype Phenotype
• PP (homozygous dominant) Purple
• pp (homozygous recessive) White
• Pp (heterozygous) Purple

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Figure 14.5 Genotype versus phenotype
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Figure 14.3 Alleles, alternative versions of a
gene
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Mendels Principles

• Law of Dominance some alleles for a trait are
  dominant and will mask alleles for a trait that
  are recessive
• Law of Segregation each parent can only pass 1
  allele for each trait If Rr genotype then only
  can be R or r not both
• Principle of independent assortment genes for
  different traits can segregate independently
  during the formation of gametes if parent is
  RrTt could pass RT, Rt, rT, or rt to offspring
  random chance

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Figure 11-3 Mendels Seven F1 Crosses on Pea
Plants
Seed Traits
Section 11-1
Seed Shape
Flower Position
Seed Coat Color
Seed Color
Pod Color
Plant Height
Pod Shape
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Wrinkled
Green
White
Constricted
Yellow
Terminal
Short
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Go to Section
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Stop Here

• Work Problems 1, 2 3 on 4 Bikini Bottom
  Genetics Sheet

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Punnett Square

• A woman who can tongue roll (Rr) is having a baby
  with her husband who can also tongue roll (RR).
  What are the chances their baby will be able to
  tongue roll?
• A Punnett square show us all possible outcomes

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Punnett Square- Determining offspringR. C.
Punnett
Place Parents Genotype Here (one RR and one Rr)
Fill every square in the column with the same
letter (always place dominant allele first
Fill every square in the row with the same letter
(always place dominant allele first
RR
Rr
RR
Rr
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Punnett Squares give us probabilities

• Offspring probabilities
• 2 RR
• 2 Rr
• 4 Total

RR
Rr
RR
Rr
Or 50 chance of having a RR offspring
2
RR
4 Possible Offspring gives us a probability- not
a certainty
100 of tongue rolling
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Or 50 chance of having a Rr offspring
2
Rr
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