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Question???. Be ready to quiz!. Genetics: Episode I A Monk, His Peas, and Genes. Ag Biology Sutherlin AST. Genetics. What is genetics? Branch of biology studying heredity What is heredity? Passing of traits from parent to offspring What are traits? Physical characteristics. Genetics.

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question
Question???
  • Be ready to quiz!
genetics
Genetics
  • What is genetics?
    • Branch of biology studying heredity
  • What is heredity?
    • Passing of traits from parent to offspring
  • What are traits?
    • Physical characteristics
genetics1
Genetics
  • Gregor Mendel
    • A monk, 1800’s Austria
    • First to study and determine factors of heredity
    • Used carefully controlled experiments: only changed one factor at a time
genetics2
Genetics
  • Why peas?
    • Produce sexually
    • Male and female parts on same flower
      • Male parts are called?
      • Female parts are called?
genetics3
Genetics
  • Pollination – male sex cells (pollen) lands on female parts (pistil)
  • Fertilization – DNA from pollen combines with DNA from ovum (egg)
    • Becomes seed
genetics4
Genetics
  • Self-pollination: male and female sex cells come from same plant
  • Cross-pollination: sex cells come from two different plants
    • Create hybrid
genetics5
Genetics
  • What did Mendel do?
    • Studied TALL traits and SHORT traits in plants (parents = P1)
    • Cross-pollinated these plants to get hybrids
    • ALL of the offspring (F1) were TALL
genetics6
Genetics
  • What did Mendel do next?
    • Took the offspring (F1), then crossed them together
    • This time, not all offspring the same.
genetics7
Genetics
  • What did Mendel do next?
    • ¾ of plants were tall
    • ¼ were short plants
    • This is called a 3:1 ratio
genetics8
Genetics

So what does this mean?

  • Unit Factors
    • Mendel concluded two factors control each trait
    • We know these are genes
      • One factor from the mother
      • One from the father
genetics9
Genetics
  • Unit Factors
    • For each gene, there are alleles
      • Different forms of each gene
      • Example: there is a gene for height (T)

It could be the Tall allele – T

It could be the Short allele - t

genetics10
Genetics
  • Unit Factors
    • Since we have two copies of each gene, three combinations
      • Two Tall (TT) alleles
      • Two Short (tt) alleles
      • One Tall allele and one

short allele (Tt)

But how is this possible?

genetics11
Genetics

What else does this mean?

  • Rule of Dominance
    • Only one allele is observable
    • Dominant alleles: observable trait
    • Recessive alleles: unobservable trait
    • So which is dominant for height in pea plants?
genetics12
Genetics
  • So what does each look like?
    • TT:
    • tt:
    • Tt:
genetics13
Genetics
  • What about cows?
    • If you cross purebred black angus cattle with red angus cattle, you get black cattle
    • What does this mean?
genetics14
Genetics
  • Two organisms can look the same, but carrying different genes
  • Phenotype: how an organism looks (think physical)
    • Tall? Short?
  • Genotype: the genes an organism has
    • Tall: could be Tt
    • Tall: could be TT
genetics15
Genetics
  • Homozygous – both alleles are the same
    • TT, tt
  • Heterozygous – alleles are different
    • Tt

All of this, by a monk, in the 1800s!

genetics16
Genetics
  • Dihybrid cross
    • Looking at just one trait (height) is monohybrid (one)
    • But what if we track more than one trait?
genetics17
Genetics
  • Mendel’s Dihybrid Cross
    • Round peas (R=round, r=wrinkled)
    • Seed color (Y=yellow, y=green)

Parents (P1)

Round Yellow X Wrinkled Green

genetics18
Genetics
  • Mendel’s Dihybrid Cross

Parents (P1)

Round Yellow X Wrinkled Green

RRYY rryy

Result? Offspring (F1) ALL Round Yellows

RrYy

genetics19
Genetics
  • Mendel’s Dihybrid Cross

F1 Cross

X

So now what do you get?

genetics20
Genetics
  • Mendel’s Dihybrid Cross
    • The point?
    • Law of Independent Assortment: genes for different traits are inherited independently of one another (green seeds do not have to be wrinkled!)
genetics21
Genetics
  • Punnett Squares
    • Tool for projecting Phenotypes and Genotypes of offspring
    • Developed by Reginald Punnett (England)
genetics22
Genetics
  • Monohybrid Punnett Square
genetics23
Genetics
  • Dihybrid Punnett Square