• Mendel’s Laws
• Beyond Mendel’s Laws
• Sex-Linked Inheritance
• Inheritance of Linked Genes
Genetics – Part I Spring 2013 - Althoff Reference: Mader & Windelspecht Ch. 11)
Lec15
• _______— the unit of heredity…passed on to offspring. 1) Each gene has a specific location on a
chromosome. 2) Each gene contains the code for specific traits to be
expressed3) Genes come in “pairs”…each pair is known as an
allele
• _______— an allele is alternative form of a gene at a particular location
• ______________— contains genes…rod-like structures in the nucleus observed
during cell division
3 Basic Terms…for starters
ALLELES of a
GENE ata genelocus
SISTER CHROMATIDS
CHROMOSOMES
DU
PLIC
ATE
D C
HR
OM
OSO
MES
SIST
ER C
HR
OM
ATI
DS
HA
VEID
ENTI
CA
L A
LLES
The Pea Picker… _____________
• Stem length• Pod shape• Seed shape• Seed Color• Flower position• Flower color• Pod color
• Tall• Inflated• Round• Yellow• Axial• Purple• Green
Pea Traits Dominant
An Austrian monk who developed the ___________________________
• Short• Constricted• Wrinkled• Green• Terminal• White• Yellow
Recessive
Mendel in his garden…..
• Stem length• Pod shape• Seed shape• Seed Color• Flower position• Flower color• Pod color
Pea Traits Dominant Recessive
_____ Mendel
• Most animal and plant breeders agreed that both sexes contributed equally to a new individual
• Same folks had not been able to account for the presence of definite ___________ (i.e., differences) among members of a family…generation after generation.
• Mendel’s MODEL OF HEREDITY does account for such ___________
Model of Heredity….consider this!• This model is compatible with the THEORY OF
EVOLUTION which states that various combinations of traits are __________ by the environment, and those combinations that lead to _________________ are the ones passed on.
or….”all living things have a __________ ancestor, but each is adapted to a particular way of life”.
• For the record, the ________________ was formulated by Charles Darwin in the 1830s but not published until 1844 and 1859, so his perspectives did not influence Mendel (remember: no internet, little publishing, long-turn around time on exchange of information).
Some key terms….• __________ – some expressed “quality” or
“structure”
• __________ trait – exerts “quality/structure” in heterozygous allele pairing
• __________ trait – exerts “quality/structure” only in homozygous allele pairing
Some more key terms….• __ generation: original parents• __ generation: first generation offspring• __ generation: second generation offspring
• _______: haploid sex cell (____________)• ________ –exact combination of alleles• ________—exact ___________ (i.e,
physical appearance)
One-trait Inheritance…and the Punnett Square
F1 gametes
ALLELES: T = tall plant t = short plant
♂♀ T t
Eggs
T
t
Spe
rm
Results from this Punnett Square
F2 ____________________
3 Tall (T) : 1 Short (t)
Translation: with this combination of alleles, There is a ____ chance of the F2 generation individual being tall and ____ chance it will be short.
The One-Trait Testcross lead to:______________________
• Each individual has __________ (alleles) for each _______
• The factors (alleles) segregate during the formation of gametes
• Each gamete contains only one factor (allele) from each pair of factors (alleles)
• ______________ gives each new individual two factors (alleles) for each trait
Mendel’s _______ law of inheritance
Genotype vs. Phenotypeusing the One-trait Inheritance
for pea plant height
Genotype(alleles)
Genotype description Phenotype
TT Homozygous dominant Tall
Tt Heterozygous Tall
tt Homozygous recessive short
Another One-Trait TestcrossF1
gametes
ALLELES: R = round seed r= wrinkled seed
♂♀ Eggs
Spe
rm
R r
R
r
TTRR
A Two-Trait TestcrossF1
gametes
ALLELES: R = round seed r= wrinkled seed
♂♀
ALLELES: T = tall plant t = short plant
PhenotypicRatio
Tall, round (TTRR, TTRr, TtRr)Tall wrinkled (TTrr, Ttrr)Short, round (ttRR, tt,Rr)Short, wrinkled (ttrr)
Spe
rm
Eggs
TR Tr tR tr
TR
Tr
tR
tr
TTRr TtRR TtRr
TTRr TTrr TtRr Ttrr
TtRR TtRr ttRR ttRr
TtRr Ttrr ttRr ttrr
The Two-Trait Testcross lead to:_________________________
__________________
• Each pair of factors (traits) ________________ independently of the other pairs
• All possible combinations can occur in the gametes
Mendel’s ____________ law of inheritance
A few things to consider…
Remember PHENOTYPE refers to _____________ “trait”…not the ______________ unless…..
A recessive trait is expressed—because a recessive trait will only appear (i.e., be expressed) if ______ ________ are recessive.ex.
AA and Aa genotypes result in same PHENOTYPE…as long as one dominant (A) allele is present
aa –then recessive trait expressed and therefore wealso know the genotype.
vs
Examples: Dominant – Recessive
• Earlobes
• Widow’s Peak
• Straight/Bent Thumb
• Cheek dimplesPRESENT ABSENT
EEor Ee
ee
WWor
Ww
SSorSs
ss
DD or Dd dd
Beyond Mendel’s Laws• Incomplete Dominance
“intermediate” phenotype possible”
Beyond Mendel’s Laws
• ____________________ “more than 2 alleles involved”
• ABO Blood Types: 3 alleles __________
Mader, p197, Fig. 11.16
Beyond Mendel’s Laws
• __________________ “trait governed by two or more sets of alleles”
• In this example, trait is controlled by 3 genes (i.e., Aa, Ba, Cc). Only those combinations represented by capital letters contribute to the ________________
______________ & Phenotype• Ex. Temperature impact on phenotype for the
Himalayan rabbit….homozygous for allele ch, which is involved in ____________ production. Encoded (gene) enzyme is active only at low temperatures….when activated it results in _______ hair (and, yes…hare!) being produced
What are the advantages to the individual for such a trait?
Snowshoe hare
winter summer-fall
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