9/20/2022
Chapter 3
The Biological Basis of
Human Variation
DARWIN’S GHOST!!
Offspring were always 50150
Variation:
1. How is it transmitted between generations?
2. Where does it come from to begin with?
Classic view ... ‘Blending Inheritance’
Eventually no variation wouldoccur
…. adaptive variation quickly diluted ???
Monk work discovered 1900s
The Monk -- Gregor Mendel -- ... and his pea garden ...
Augustinian convent in
Brno, Czech Republic
Starting with pure strains of yellow and green peas...
YELLOW X GREEN
Expecting to get intermediate
F1: all YELLOW ?? X YELLOW
GREEN is lost ? Expecting to get all yellow
F2: YELLOW + GREEN !?!?!
GREEN is back ?
Original variation is first lost and then re-appears!!
How is this possible??
Copyright © 2015 by Nelson Education Ltd. 1
, 9/20/2022
Mendel’s hypothesis ... Particulate Inheritance
Discrete particles of information transmitted to offspring...
... and some particles dominant to others
“Y” particle produces “yellow”
“y” particle produces “green”
And “Y” dominant to “y”
Each parent has a pair of particles, either YY Yy or yy...
... and contributes one of their particles to an offspring.
Peas reviewed in light of particulate hypothesis:
Pure strains of yellow (YY) and green (yy)
FO: YY X yy
Y or Y ; y or y
F1: all Yy (i.e. YELLOW) X Yy
So pattern is
consistent with
Y or y Y or y hypothesis of
particulate inheritance
F2: YY Yy yY yy (i.e. YELLOW and GREEN)
Mysterious particles controlling TRAITS = GENES
... contained on chromosomes (paired DNA strands) found in every cell Phenotype resultofgenotype
X
X
X
Different forms of the particles/genes = ALLELES
Different allele combinations = GENOTYPES: YY Yy yy
X X X
Outward traits they code for = PHENOTYPES: yellow/green
Sexual reproduction involves (in each mate) separating
paired strands of DNA on each chromosome, contributing
one strand (hence one gene in the pair) to each gamete
prior to mating… a process called meiosis.
Copyright © 2015 by Nelson Education Ltd. 2
Chapter 3
The Biological Basis of
Human Variation
DARWIN’S GHOST!!
Offspring were always 50150
Variation:
1. How is it transmitted between generations?
2. Where does it come from to begin with?
Classic view ... ‘Blending Inheritance’
Eventually no variation wouldoccur
…. adaptive variation quickly diluted ???
Monk work discovered 1900s
The Monk -- Gregor Mendel -- ... and his pea garden ...
Augustinian convent in
Brno, Czech Republic
Starting with pure strains of yellow and green peas...
YELLOW X GREEN
Expecting to get intermediate
F1: all YELLOW ?? X YELLOW
GREEN is lost ? Expecting to get all yellow
F2: YELLOW + GREEN !?!?!
GREEN is back ?
Original variation is first lost and then re-appears!!
How is this possible??
Copyright © 2015 by Nelson Education Ltd. 1
, 9/20/2022
Mendel’s hypothesis ... Particulate Inheritance
Discrete particles of information transmitted to offspring...
... and some particles dominant to others
“Y” particle produces “yellow”
“y” particle produces “green”
And “Y” dominant to “y”
Each parent has a pair of particles, either YY Yy or yy...
... and contributes one of their particles to an offspring.
Peas reviewed in light of particulate hypothesis:
Pure strains of yellow (YY) and green (yy)
FO: YY X yy
Y or Y ; y or y
F1: all Yy (i.e. YELLOW) X Yy
So pattern is
consistent with
Y or y Y or y hypothesis of
particulate inheritance
F2: YY Yy yY yy (i.e. YELLOW and GREEN)
Mysterious particles controlling TRAITS = GENES
... contained on chromosomes (paired DNA strands) found in every cell Phenotype resultofgenotype
X
X
X
Different forms of the particles/genes = ALLELES
Different allele combinations = GENOTYPES: YY Yy yy
X X X
Outward traits they code for = PHENOTYPES: yellow/green
Sexual reproduction involves (in each mate) separating
paired strands of DNA on each chromosome, contributing
one strand (hence one gene in the pair) to each gamete
prior to mating… a process called meiosis.
Copyright © 2015 by Nelson Education Ltd. 2
