Download Extending Mendel Student Notes

1/10/2014
Which of these genes are most likely to
segregate as a unit?
Figure 14.8
EXPERIMENT
YYRR
P Generation
yyrr
Gametes YR
yr
F1 Generation
YyRr
Hypothesis of
dependent assortment
Predictions
Sperm
or
Predicted
offspring of
F2 generation
Genetics: Part III
Hypothesis of
independent assortment
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YR
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YR
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yr
Eggs
Extending Mendel
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YYRR
YyRr
YyRr
yyrr
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Yr
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yR
Eggs
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yR
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yr
YR
YYRR
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YyRR
YYRr
YYrr
YyRr
Yyrr
YyRR
YyRr
yyRR
yyRr
YyRr
Yyrr
YyRr
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Phenotypic ratio 3:1
1/
yr
4
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yyRr
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yyrr
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Phenotypic ratio 9:3:3:1
RESULTS
315
108
101
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Phenotypic ratio approximately 9:3:3:1
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Which of these genes are most likely to
segregate as a unit?
In Drosophila…..
Curriculum Framework
Traits for wings, leg
length, and eye color are
carried on the same
chromosome. These genes
are linked together on the
same chromosome and
will sort into the same
gamete.
3.A.3.b.2
Genes that are adjacent and close to each other
on the same chromosome tend to move as a unit;
the probability that they will segregate as a unit
is a function of the distance between them.
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Crossover Value
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Calculating Crossover
expected
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Extending Mendelian Genetics
for a Single Gene
• Inheritance of characters by a single gene
may deviate from simple Mendelian patterns
in the following situations:
– When alleles are not completely dominant or
recessive
– When a gene has more than two alleles
– When a gene produces multiple phenotypes
unexpecte
d
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Figure 14.10-1
Degrees of Dominance
P Generation
White
CWCW
Red
CRCR
• Complete dominance occurs when
phenotypes of the heterozygote and
dominant homozygote are identical
• In incomplete dominance, the phenotype
of F1 hybrids is somewhere between the
phenotypes of the two parental varieties
• In codominance, two dominant alleles
affect the phenotype in separate,
distinguishable ways
Gametes
CR
CW
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Figure 14.10-2
Figure 14.10-3
P Generation
Multiple Alleles
P Generation
White
CWCW
Red
CRCR
Gametes
1/
2
CW
F1 Generation
Pink
CRCW
Gametes 1/2 CR
CR
Gametes
CW
CR
F1 Generation
White
CWCW
Red
CRCR
Pink
CRCW
Gametes 1/2 CR
CW
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2
CW
Sperm
1/
2
F2 Generation
1/
2
CR
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CW
Eggs
CR
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2
CW
CRCR CRCW
CRCW CWCW
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Figure 14.11
Allele
Carbohydrate
IA
IB
i
• Sara, who is type O, claims that Ira is the
father of her baby. The baby has type O blood.
Ira is blood type B. Is it possible that Ira is the
father?
none
B
A
Solve It
Key to blood type genotypes
(a) The three alleles for the ABO blood groups and their
carbohydrates
(b) Blood group genotypes and phenotypes
Genotype
IAIA or IAi
IBIB or IBi
IAIB
ii
A
B
AB
O
Red blood cell
appearance
Phenotype
(blood group)
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Polygenic Inheritance
Curriculum Framework
Solve It
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• 3.A.4: The inheritance pattern of many traits
cannot be explained by simple Mendelian
genetics.
a. Many traits are the product of multiple genes
and/or physiological processes.
1. Patterns of inheritance of many traits do not follow
ratios predicted by Mendel’s laws and can be
identified by quantitative analysis, where observed
phenotypic ratios statistically differ from the
predicted ratios.
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Figure 14.13
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Influence of Environment
AaBbCc
AaBbCc
Sperm
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Created by:
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Eggs
Debra Richards
Coordinator of K‐12 Science Programs
Bryan ISD
Bryan, TX
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Phenotypes:
Number of
dark-skin alleles:
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64
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64
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