Transcript The Work of Gregor Mendel

The Work of Gregor Mendel
11-1
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Every living thing has a set of
characteristics inherited from its parents
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Scientists realize that heredity holds the
key to understanding what makes us
unique
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As a result, genetics is at the core of a
revolution in understanding biology
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Genetics - scientific study of heredity
Gregor Mendel’s Peas
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Gregor Mendel
 Austrian monk, born 1822
 Studied science and math
 Worked in a monastery - in charge of the garden
 Taught at the high school
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His work in the garden changed biology forever
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Mendel conducted his famous genetic
experiments with garden peas
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Pea plants have flowers that contain
both male and female parts
Male - stamen (anthers & filament), pollen
 Female - carpel( stigma, style, ovary), eggs
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When pollen fertilizes an egg cell, a
seed for a new plant is formed
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Pea plants normally reproduce by selfpollination
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Seeds that are produced by selfpollination inherit all of their
characteristics from a single plant
Known as a true breeding plant
 Produces offspring identical to parent
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Mendel had a supply of true-breeding
pea plants
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Basis for his experiments
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Noted that pea plants have 7 contrasting
traits
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Height, seed shape, seed color, seed coat
color, flower position, pod shape, pod color
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Plants can also cross-pollinate
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Mendel manipulated this concept during
his experiments
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He removed the male plant parts from
several plants, that had a contrasting traits
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Carefully dusted pollen from one plant onto
stigma of plant with contrasting trait
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Studied the offspring of the crosses
Genes & Dominance
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In Mendel’s cross-breeding
experiments, he was studying the traits
of the pea plants
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Trait - a specific characteristic, like seed
color, that varies from one individual to
another
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The offspring that resulted from
Mendel’s cross-breeding were known as
hybrids
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Have parents with different traits
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Ex: tall x short
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The first set of offspring are called the
F1 generation, or first filial
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Offspring in the F1 generation only
showed traits from one of the parents
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Mendel made 2 conclusions from these
experiments:
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Biological inheritance is determined by
factors that are passed from one
generation to the next
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Today, those factors are called genes
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Mendel’s studies involved genes that had two
contrasting forms
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The different forms of a gene are called alleles
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His second conclusion is the principle of
dominance
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Some alleles are dominant and others are
recessive
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Dominant alleles are always expressed
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Recessive alleles are only expressed
when paired up with another recessive
allele
Segregation
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Mendel wondered what happened to the
recessive traits in the F1 crosses
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Mendel allowed all of the plants of the
F1 to self-pollinate, creating the F2 or
second filial generation
The F1 Cross
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In the F2 generation, the recessive trait
appeared in about 1/4 of the offspring
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The remaining 3/4 still showed the
dominant trait
Explaining the F1 Cross
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Mendel assumed that at some point, the
contrasting alleles were separated, or
segregated
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He believed that this happened during
the formation of gametes - sex cells
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