Genetic Crosses Section 9.2. Genotype The genetic makeup of an organism Consists of the alleles...
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Transcript of Genetic Crosses Section 9.2. Genotype The genetic makeup of an organism Consists of the alleles...
GenotypeGenotype
The genetic makeup of an organismThe genetic makeup of an organism
Consists of the alleles that the organism Consists of the alleles that the organism inherits from its parentsinherits from its parents
Example: white flowering pea plantsExample: white flowering pea plants
(recessive trait (recessive trait pppp) )
PhenotypePhenotype
The appearance of an organism as a The appearance of an organism as a result of its genotyperesult of its genotype
Example: pea plants that are PP or PpExample: pea plants that are PP or Pp
will have purple flowerswill have purple flowers
HomozygousHomozygous
Both alleles of a pair are alikeBoth alleles of a pair are alike
May be homozygous dominant (PP) or May be homozygous dominant (PP) or homozygous recessive (pp)homozygous recessive (pp)
HeterozygousHeterozygous
The two alleles in the pair are differentThe two alleles in the pair are different
Example: a pea plant that is Example: a pea plant that is heterozygous for flower color heterozygous for flower color
would be Pp (purple flowers)would be Pp (purple flowers)
ProbabilityProbability
The likelihood that a specific event will The likelihood that a specific event will occuroccur
May be expressed as a decimal, a May be expressed as a decimal, a percentage, or a fractionpercentage, or a fraction
Probability = Probability = number of times an event is number of times an event is
expected to happen_____________expected to happen_____________
number of opportunities for an eventnumber of opportunities for an event
to happento happen
Example: yellow pea seeds appeared 6022 times and Example: yellow pea seeds appeared 6022 times and
green pea seeds appeared 2001 times in the Fgreen pea seeds appeared 2001 times in the F22
Total (6022 + 2001 = 8023) Total (6022 + 2001 = 8023)
What is the probability that the dominant trait will appear What is the probability that the dominant trait will appear in a similar cross?in a similar cross?
P = P = 60226022 = .75 (or 75% or ¾ ) = .75 (or 75% or ¾ )
80238023
Monohybrid CrossMonohybrid Cross
A cross between individuals that involves A cross between individuals that involves one pair of contrasting traitsone pair of contrasting traits
Example: crossing a pea plant that is Example: crossing a pea plant that is pure for white flowers (pp) with one that pure for white flowers (pp) with one that is pure for purple flowers (PP)is pure for purple flowers (PP)
Punnett SquarePunnett Square
Diagram used to predict the outcome of Diagram used to predict the outcome of certain crossescertain crosses
Predicts the probability of inherited traitsPredicts the probability of inherited traits
Homozygous X HomozygousHomozygous X Homozygous
white flowerwhite flower
(pp)(pp)
p pp p
purple purple
flower (PP) P Pp Ppflower (PP) P Pp Pp
P Pp PpP Pp Pp
Homozygous X HeterozygousHomozygous X Heterozygous
black coatblack coat
(Bb)(Bb)
B bB b
black coatblack coat
(BB) B BB Bb(BB) B BB Bb
B BB BbB BB Bb
Heterozygous X HeterozygousHeterozygous X Heterozygous
black coatblack coat
(Bb)(Bb)
B bB b
black coatblack coat
(Bb) B BB Bb(Bb) B BB Bb
b Bb bbb Bb bb
TestcrossTestcross
An individual of an unknown genotype is An individual of an unknown genotype is crossed with a homozygous recessive crossed with a homozygous recessive individualindividual
Can be used to determine the genotype Can be used to determine the genotype of any individual whose phenotype is of any individual whose phenotype is dominant (example: BB or Bb)dominant (example: BB or Bb)
Incomplete DominanceIncomplete Dominance
Occurs when two or more alleles Occurs when two or more alleles influence the phenotypeinfluence the phenotype
Example: four o’clock flowersExample: four o’clock flowers
RR = redRR = red
Rr = pinkRr = pink
rr = whiterr = white
Incomplete Dominance in Incomplete Dominance in Four O’clock FlowersFour O’clock Flowers
Pink flowerPink flower (Rr)(Rr) R r R r Pink flowerPink flower (Rr) R RR Rr (Rr) R RR Rr
r Rr rrr Rr rr
Phenotypic ratio: 1 red: 2 pink:1 white Phenotypic ratio: 1 red: 2 pink:1 white
CodominanceCodominance
Occurs when both alleles for a gene are Occurs when both alleles for a gene are expressed in a heterozygous offspringexpressed in a heterozygous offspring
Neither allele is dominant or recessiveNeither allele is dominant or recessive
Example: roan horses R = red coatExample: roan horses R = red coat
(RR`) R` = white(RR`) R` = white
Dihybrid CrossDihybrid Cross
A cross between individuals that involves A cross between individuals that involves two pairs of contrasting traitstwo pairs of contrasting traits
Must consider how the four alleles from Must consider how the four alleles from each parent can combineeach parent can combine
Homozygous X HomozygousHomozygous X Homozygous
wrinkled & greenwrinkled & green
(rryy)(rryy)
ry ry ry ryry ry ry ry
round & round & RY RrYyRY RrYy RrYy RrYy RrYy RrYy RrYy RrYy
yellow yellow RY RrYy RrYy RrYy RrYy RY RrYy RrYy RrYy RrYy
(RRYY) (RRYY) RY RrYy RrYy RrYy RrYyRY RrYy RrYy RrYy RrYy
Ry RrYy RrYy RrYy RrYyRy RrYy RrYy RrYy RrYy
Heterozygous X HeterozygousHeterozygous X Heterozygous
round & yellowround & yellow
(RrYy)(RrYy)
RY Ry rY ryRY Ry rY ry
round & round & RY RRYY RRYy RrYY RrYyRY RRYY RRYy RrYY RrYy
yellow yellow Ry RRYy RRyy RrYy Rryy Ry RRYy RRyy RrYy Rryy
(RrYy) (RrYy) rY RrYY RrYy rrYY rrYyrY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryyry RrYy Rryy rrYy rryy
Four PhenotypesFour Phenotypes
9/16 round & yellow9/16 round & yellow (genotypes RRYY, RRYy, RrYY, and RrYy)(genotypes RRYY, RRYy, RrYY, and RrYy)
3/16 round & green3/16 round & green (genotypes RRyy and Rryy)(genotypes RRyy and Rryy)
3/16 wrinkled & yellow3/16 wrinkled & yellow (genotypes rrYY and rrYy)(genotypes rrYY and rrYy)
1/16 wrinkled & green1/16 wrinkled & green (genotype rryy)(genotype rryy)