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Important Terms
Dominant TraitDominant Trait: the trait that shows : the trait that shows when two different alleles for the trait are when two different alleles for the trait are inherited ex- tongue rolling inherited ex- tongue rolling
Recessive TraitRecessive Trait: the trait that seems to : the trait that seems to disappear when two different alleles for the disappear when two different alleles for the trait are inherited ex- non-rollingtrait are inherited ex- non-rolling
Important Terms
PhenotypePhenotype: an organism’s physical : an organism’s physical appearanceappearanceex- tall, short, white flowers, green seedsex- tall, short, white flowers, green seeds
GenotypeGenotype: an organism’s gene code: an organism’s gene codeex- Tt, TT, tt, WW, Ww, yyex- Tt, TT, tt, WW, Ww, yy
Important Terms
HeterozygousHeterozygous: having dissimilar pairs of : having dissimilar pairs of alleles for any hereditary characteristic alleles for any hereditary characteristic ex- Tt, Ss, Ll, Mm (hybrid)ex- Tt, Ss, Ll, Mm (hybrid)
HomozygousHomozygous: having identical pairs of : having identical pairs of alleles for any given pair of heredity alleles for any given pair of heredity characteristic characteristic ex- tt, SS, LL, mm (purebred)ex- tt, SS, LL, mm (purebred)
Punnett Squares Used to illustrates how Used to illustrates how
the parents’ alleles might the parents’ alleles might combine in offspring. combine in offspring.
Used to predict the Used to predict the probability or % chance probability or % chance of an offspring's of an offspring's genotype and phenotypegenotype and phenotype
Reginald Punnet developed the Punnett Square in 1910
Punnett Squares The top of the Punnett Square shows one of The top of the Punnett Square shows one of
the parent’s alleles, the side of the Punnett the parent’s alleles, the side of the Punnett square shows the other parent’s alleles for square shows the other parent’s alleles for the trait the trait
t t
T
T
Mendel’s Laws of InheritanceLaw of Dominance: In heterozygous genotypes,
dominant alleles hide recessive alleles when both are inherited by an organism.
Mendel’s Laws of Inheritance The Law of Segregation:
Each organism has 2 alleles for a gene and only one allele from each gene pair will be passed on to the offspring.
Homozygous/Heterozygous
Cross a homozygous Cross a homozygous dominant tall plant dominant tall plant with a homozygous with a homozygous recessive short plant. recessive short plant.
What letters would you use to represent this cross?
Dominant trait = tall Dominant trait = tall
Recessive trait = shortRecessive trait = short
T = tall T = tall t = short t = short
Hmzg / Htzg
What is the genotype of a homozygous What is the genotype of a homozygous dominant tall plant?dominant tall plant?
GenotypeGenotype
% % TTTT
% % TtTt
% tt% tt
TT TT
TT x ttTT x tt
What is the genotype of a homozygous What is the genotype of a homozygous recessive short plant?recessive short plant? tt tt
t t
T
T
PhenotypePhenotype
% tall% tall
% % shortshort
Tt Tt
Tt Tt
0
100
0
0
100
2. Cross a heterozygous brown haired rabbit 2. Cross a heterozygous brown haired rabbit with a homozygous recessive white haired with a homozygous recessive white haired rabbit.rabbit.
o What letters would you use to represent this cross?
Dominant trait = Dominant trait = brown hairbrown hair
Recessive trait = Recessive trait = white hairwhite hair
B = brownB = brown b = whiteb = white
What is the genotype of a heterozygous What is the genotype of a heterozygous brown haired rabbit?brown haired rabbit?
GenotypeGenotype
% % BBBB
% % BbBb
% % bbbb
Bb Bb
Bb x bbBb x bb
What is the genotype of a homozygous What is the genotype of a homozygous recessive white haired rabbit?recessive white haired rabbit? bb bb
b b
B
b
PhenotypePhenotype
% % brownbrown
% % whitewhite
bb bb
Bb Bb
0
50
50
50
50
3.. Cross a homozygous dominant 3.. Cross a homozygous dominant long haired guinea pig with a long haired guinea pig with a heterozygous long haired guinea pig.heterozygous long haired guinea pig.
o What letters would you use to represent this cross?
Dominant trait = Dominant trait = long hairlong hair
Recessive trait = Recessive trait = short hairshort hair
L = longL = long l = short l = short
What is the genotype of a homozygous What is the genotype of a homozygous dominant long haired guinea pig?dominant long haired guinea pig?
GenotypeGenotype
% % LLLL
% % LlLl
% ll% ll
LLLL
LL x LlLL x Ll
What is the genotype of a heterozygous What is the genotype of a heterozygous long haired guinea pig?long haired guinea pig? Ll Ll
L l
L
L
PhenotypePhenotype
% long% long
% % shortshort
LL Ll
LL Ll
50
50
0
0
100
4. Cross a heterozygous wrinkly 4. Cross a heterozygous wrinkly elephant with another heterozygous elephant with another heterozygous wrinkly elephant.wrinkly elephant.
What letters would you use to represent this cross?
Dominant trait = Dominant trait = wrinkly skinwrinkly skin
Recessive trait = Recessive trait = smooth skinsmooth skin
W = wrinklyW = wrinkly w = smooth w = smooth
What is the genotype of a heterozygous What is the genotype of a heterozygous wrinkly-skinned elephant?wrinkly-skinned elephant?
GenotypeGenotype
% % WWWW
% % WwWw
% % wwww
WwWw
Ww x WwWw x Ww
What is the genotype of a heterozygous What is the genotype of a heterozygous wrinkly-skinned elephant?wrinkly-skinned elephant? WwWw
W w
W
w
PhenotypePhenotype
% % wrinklywrinkly
% % smoothsmooth
Ww ww
WW Ww
25
50
25
25
75
PhenotypePhenotype
% round% round
% % wrinkledwrinkled
5. A plant that is homozygous dominant for round seeds is crossed with a heterozygous plant. What is the probability that the offspring will have
wrinkled seeds?
RR x RrRR x Rr
R r
R
R
RR Rr
RR Rr
R = round
GenotypeGenotype
% % RRRR
% Rr% Rr
% rr% rr
r = wrinkled
50
50
0
0
100