Chapter 12

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Chapter 12 Patterns of Heredity and Human
Genetics

• Objectives
• Identify information presented on a karyotype
• Recognize the difference between male and female
  karyotypes
• Distinguish between normal and abnormal
  karyotypes

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Take out a sheet of paper and write your name
along with your lab partners.

• 1. Look Figure 12.20 on page 329. Explain what
  you think the picture is showing?
• 2. What do you think the numbers as well as
  letters on the photograph represent?

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Karyotype pg. 329

• Chromosomes come in pairs, inherited from parents
• Half from mom half from dad
• Humans have 23 pairs of chromosomes, 46 total.
• Any more or less abnormality
• Sex Chromosomes Called X and Y
• Autosomes all non-sex chromosomes

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Karyotype Fig. 12.20 pg. 329

• Picture of cell taken during the process of
  metaphase
• 3. Why metaphase?
• 4. Looking at the Figure 12.20, how are the
  chromosomes arranged?
• 5. Do you think male and female karyotypes are
  the same? Explain.
• Chromosomes arranged by length, banding pattern,
  centromere location
• Comparison against a normal karyotype

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Pedigree

• Pedigree map of inheritance of genetic traits
  from generation to generation

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Symbols on a Pedigree

• Circle Female Square Male
• Shaded Affected Unshaded Unaffected
• Adjoining line Married/Mating
• Connected by an adjoining line Offspring
• Roman Numeral Generation

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Textbook pg. 310 Fig. 12.2

• 7. How many generations are shown?
• 8. How many offspring did I-1 and I-2 have?
• 9. How many boys did III-3 and III-4 have?
• 10. How many girls did II-1 and II-2 have?
• 11. What kind of trait (dominant or recessive) is
  being passed down?
• 12. What genotypes must I-1 and I-2 be in order
  to have a child with this trait?
• 13. What is the probability that they would have
  this type of child? Show a Punnett square

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Recessive Heredity

• Caused by recessive alleles
• Attached earlobes, Cystic fibrosis (defective
  protein leads to excessive mucus production in
  lungs), Albinism
• Individual will only display the recessive
  phenotype if its genotype is homozygous recessive

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Dominant Heredity

• Caused by dominant allele
• Freckles, Widows peak, Hitchhickers thumb,
  Huntingtons disease (brain degeneration, doesnt
  appear until later in age), immunity to poison
  ivy
• Individual will display the dominant phenotype if
  its genotype is heterozygous or homozygous
  dominant

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When Heredity Follows Different Rules

• Chapter 12, Section 2

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Incomplete Dominance

• Incomplete Dominance phenotype of a
  heterozygote is in between the dominant
  recessive phenotypes, appearance of a third
  phenotype.
• No Longer Upper and Lowercase letters A or a
• Flowers known as Snapdragons come in 3 colors but
  have 2 alleles, R and R
• RR White
• RR or RR Pink
• RR Red

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Sample Problems

• Cross the following snapdragons and give the
  genotype and phenotype ratios.
• Red x White Phenotypic Ratio
• White Pink Red
• Genotypic Ratio
• RR RR RR
• Pink x Pink Phenotypic Ratio
• White Pink Red
• Genotypic Ratio
• RR RR RR

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Text pg. 316 Figure 12.7

• Red x White all pink
• Pink x Pink 1Red 2Pink 1White

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Genetics Review

• Mendelian Genetics Simple Dominant Recessive
  Traits (Tall TT or Tt or short tt)
• Incomplete Dominance 3 phenotypes (FF red,
  FF pink, FF white)
• Pedigree Map to show how traits are passed from
  parent to offspring (not shaded doesnt have
  trait, half shaded carrier, shaded has trait

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Codominance

• Both alleles for a gene are expressed in a
  heterozygous individual
• Black Feathers FBFB Black Feathers
• White Feathers FW FW White
• When the 2 alleles are combined a chicken with
  both black and white feathers is created.
• Erminette chickens FBFW Black White
• Neither allele is dominant or recessive

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Codominance Practice Problems

• Cross a chicken that is homozygous for the black
  alleles with a chicken that is homozygous for the
  white alleles.
• What color feathers did the offspring have?
• Cross 2 chickens from the F1 generation to make
  the F2 generation?
• What color feathers did the offspring have?

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Blood Types

• BLOOD TYPE.ppt

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Sex Determination Sex-linked Inheritance

• Combination of sex chromosomes (X and Y)
  determine an individuals gender
• Males XY, X chromosome comes from mom Y
  chromosome comes from dad
• Females XX, both mom dad give an X chromosome
• Sex-linked Traits traits controlled by genes on
  sex chromosomes

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• Red-Green colorblindness
• Hemophilia (blood doesnt clot properly)
• Male Pattern Baldness
• Duchenne Muscular Distrophy (muscular
  degeneration leading to eventual paralysis)

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• Most of sex-linked traits are found on genes on
  the X chromosome (X-linked trait) because it is
  larger than the Y chromosome
• X-linked traits display more in males because
  they only have 1 X chromosome, whereas females
  get 2 X chromosomes so they can be carriers of
  the trait but not display the phenotype

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Color Blindness - Recessive Trait B Normal
b color blind

• Males
• XBY Normal XbY Color Blind
• Females
• XBXB Normal
• XBXb Carrier (Normal)
• XbXb Color Blind
• Can males be carriers for color blindness? Why or
  why not?

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Polygenic Inheritance

• Characteristics that are influenced by several
  genes