© k. malone, 2005 chapter 11 introduction to genetics p. 64
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XFirst Generation (F1)
100% pink!!!
Second Generation (F2)
X
3 pink, 1 blue - ¾ pink (75%), ¼ blue (25%)How did this How did this
happen?happen?
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Section 11-1
Genetics!!!
• Patterns of Inheritance• You inherit traits (physical
characteristics) from your parents- Heredity!
• Heredity is what makes you unique– Examples of Traits:
• Blue, Green, Brown, Black, Hazel Eye color
• GeneticsGenetics = the scientific study of heredityand its importance in biology
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Gregor Mendel
•Gregor Mendel (1822), an Austrian monk who studied inheritance patterns in pea plants, his work is now considered the foundation of modern genetics– He worked with ordinary
garden peas, planted in the garden at his monastery.
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What Mendel Found• Mendel studied 7 different pea plant
traits that varied from one individual plant to the next (like human traits!)
• These traits had 2 forms, such as either green seeds or yellow seeds, smooth pods or wrinkled pods– He crossed plants with each of the 7
contrasting characteristics and studied their offspring
• P = represents the parent generation
• F (from the Latin word fillius and filia- son and daughter) are the offspring
• F1 = first generation
• F2 = second generation
• Hybrids = offspring of crosses between parents with different traits
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Mendel’s Results
Seed Shape
Seed Color
Seed Coat Color
PodShape
PodColor
FlowerPosition
FlowerHeight
wrinkled green white
round yellow gray
constricted yellow terminal short
smooth greenaxial
tallRound dominant
Yellow dominant
Gray dominant
Smooth dominant
Green dominant
Axial dominant
Tall dominant
All the F1 plants expressed only the dominant trait!
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Mendel’s Principles of Heredity
• Mendel learned 2 principles from these experiments:1. Biological inheritance is
determined by factors (we call them genes) that are passed from one generation to the next, Genes = chemical factors that
determine traits – each trait is controlled by 1 gene that occurs in 2 contrasting forms or alleles
Allele = a different form
of a gene
Hello!
2. Principle of Dominance: some alleles are dominant and others are recessive
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Principle of Dominance
Eeek!
• An organism with a dominant allele for a particular form of a trait will always exhibit that form of the trait
• In other words, if you have the dominant allele, you will express that dominant trait
• An organism with a recessive allele for a particular form of a trait will exhibit that form only when the dominant allele is not present
• In other words, you must have 2 recessive alleles to express the recessive trait
I’m Dominant!! Tall =
TT or Tt
Short = tt
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Where did the recessive traits go?
• Mendel wanted to know why all his F1 plants expressed only dominant traits ?????
• He wondered, “Had all the recessive traits disappeared? Or were they still present in the F1 plants?”
• To answer this question, he allowed his F1 plants to self-pollinate
F1 X F1 F2
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Mendel’s Experiment
P generation
tall short
F1 generation
talltall
F2 generation
tall tall tall short
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