CH11
Fig. 1. Difference between the outcomes from blending and from particulate inheritance. In post-Mendelian
terms, we assume a single diallelic locus, and hence three diploid genotypes (AA, blue; Aa, green; aa, yellow).
Under particulate inheritance, the population's variability is preserved from generation to generation. In
contrast, the conventional wisdom of Darwin's day saw offspring inherit a blend of parents' characteristics, here
represented as the average of the two parental shadings. The result is that the variability diminishes in
successive generations (the variance is halved each generation if mating is at random) SCIENCE MAGAZINE B.
Figure 11.2
Technique
1
Why are peas so
great to work with?
2
Parental
generation
(P)
3
Stamens
Carpel
4
Results
5
First filial
generation
offspring
(F1)
Figure 11.4
Review of terms….
What is a locus? What are alleles?
Allele for purple flowers
Locus for flower-color gene
•
•
•
Pair of
homologous
chromosomes
Is this individual with these chromosomes in their cells homozygous or heterozygous?
What is the genotype?
If purple flower allele is dominant, what is the phenotype?
Allele for white flowers
Figure 11.3-3
Experiment
P Generation
(true-breeding
parents)
Purple flowers
White flowers
F1 Generation
(hybrids)
So all F1 are Pp
All plants had purple flowers
Self- or cross-pollination
What
What are the genotypes of the gametes of these Pp plants?
F2 Generation
705 purple-flowered 224 white-flowered
plants
plants
Figure 11.6
3
Phenotype
Genotype
Purple
PP
(homozygous)
Purple
Pp
(heterozygous)
1
2
1
Purple
Pp
(heterozygous)
White
pp
(homozygous)
Ratio 3:1
Ratio 1:2:1
1
Figure 11.3-3
Experiment
P Generation
(true-breeding
parents)
Purple flowers
White flowers
F1 Generation
(hybrids)
All plants had purple flowers
Self- or cross-pollination
F2 Generation
705 purple-flowered 224 white-flowered
plants
plants
Imagine crossing a pea heterozygous at the loci for flower color
(white versus purple) and seed color (yellow versus green) with a
second pea homozygous for flower color (white) and seed color
(yellow). What types of gametes will the first pea produce?
•
•
•
•
•
two gamete types: white/white and purple/purple
two gamete types: white/yellow and purple/green
four gamete types: white/yellow, white/green, purple/yellow,
and purple/green
four gamete types: white/purple, yellow/green, white/white,
and purple/purple
one gamete type: white/purple/yellow/green
Imagine crossing a pea heterozygous at the loci for flower color
(white versus purple) and seed color (yellow versus green) with a
second pea homozygous for flower color (white) and seed color
(yellow). What types of gametes will the first pea produce?
•
•
•
•
•
two gamete types: white/white and purple/purple
two gamete types: white/yellow and purple/green
four gamete types: white/yellow, white/green,
purple/yellow, and purple/green
four gamete types: white/purple, yellow/green, white/white,
and purple/purple
one gamete type: white/purple/yellow/green
For this cross assume white is dominant and yellow is
dominant…. What different offspring will you get????
Figure 11.8
Experiment
YYRR
P Generation
yyrr
Gametes YR
yr
F1 Generation
YyRr
Hypothesis of
dependent assortment
Predictions
Hypothesis of
independent assortment
Sperm
or
Predicted
offspring in
F2 generation
¼ YR ¼ Yr ¼ yR ¼ yr
Sperm
½ YR ½ yr
¼ YR
½ YR
Eggs
½ yr
YYRR YyRr
YyRr
¾
yyrr
¼ Yr
Eggs
¼ yR
YYRR YYRr
YyRR YyRr
YYRr
YYrr
YyRr
Yyrr
YyRR YyRr
yyRR
yyRr
YyRr
yyRr
yyrr
¼
Phenotypic ratio 3:1
¼ yr
9
16
3
16
Yyrr
3
16
1
16
Phenotypic ratio 9:3:3:1
Results
315
108
101
32
Phenotypic ratio approximately 9:3:3:1
Twins…EACH of you should respond to each question on
paper after you have a discussion in your group about your
response!
1. Why are twins raised in different households considered so
valuable to biologists?
2. What is heritability? (they talk about height in this article)
FYI these graphs are not a result of twin analyses but are a
result of studying inheritance through regression statistics.
3. Which graphs show hi, medium and low heritability?
4. What might a graph with the actual heritability of height look
like? Draw one!
5. If heritability is high like .8 does that mean the environment
is not important?
6. Why do we freak out when we learn the heritability of IQ is
something like .75? Historical connections?
7. What are we learning from situations where identical twins
differ in specific substantial ways despite being raised in the
same household? (autism example)
8. So what is epigenetics?
9. There are several analogies towards the end of the articlewhat were they?
http://erinjenne.blogspot.com/2011_02_01_archive.html
Figure 11.10-2
P Generation
Red
CRCR
Gametes
White
CWCW
CR
CW
Pink
CRCW
F1 Generation
Gametes ½ CR ½ CW
Today…..What is this called?
Is this blending inheritance???
Albinism in humans occurs when both alleles at a locus
produce defective enzymes in the biochemical pathway
leading to melanin. Given that heterozygotes are normally
pigmented, which of the following statements is/are
correct?
•
•
•
•
•
One normal allele produces as much melanin as two
normal alleles.
Each defective allele produces a little bit of melanin.
Two normal alleles are needed for normal melanin
production.
The two alleles are codominant.
The amount of sunlight will not affect skin color of
heterozygotes.
Imagine a locus with four different alleles for fur color in an
animal. The alleles are named Da, Db, Dc, and Dd. If you
crossed two heterozygotes, DaDb and DcDd, what genotype
proportions would you expect in the offspring?
•
•
•
•
•
25% DaDc, 25% DaDd, 25% DbDc, 25% DbDd
50% DaDb, 50% DcDd
25% DaDa, 25% DbDb, 25% DcDc, 25% DdDdDcDd
50% DaDc, 50% DbDd
25% DaDb, 25% DcDd, 25% DcDc, 25% DdDd
When a disease is said to have a
multifactorial basis, it means that
• both genetic and environmental factors
contribute to the disease.
• it is caused by a gene with a large number of
alleles.
• it affects a large number of people.
• it has many different symptoms.
• it tends to skip a generation.
Figure 11.12
What is this
called????
BbEe
BbEe
Sperm
What is going
Eggs
on????
¼ BE
¼ bE
¼ BE
¼ Be
¼ be
BBEE
BbEE
BBEe
BbEe
BbEE
bbEE
BbEe
bbEe
BBEe
BbEe
BBee
Bbee
BbEe
bbEe
Bbee
bbee
¼ bE
¼ Be
¼ be
9
:
3
: 4
Figure 11.13
AaBbCc
AaBbCc
Sperm
1
1
1
1
1
Eggs
1
1
1
1
1
8
8
1
8
1
1
8
8
1
8
1
1
8
8
8
8
8
8
8
8
8
8
Phenotypes:
Number of
dark-skin alleles:
1
64
0
6
64
1
15
64
2
20
64
3
15
64
4
6
64
5
1
64
6
1
64