Download two traits

7.4 TWO TRAIT CROSSES
Lesson Objectives

Students will be able to:
 Predict
offspring inheritance of two traits
Gametes



Gametes have 1 allele for each gene
Alleles for each trait can be combined in many
different combinations in the gametes
For example –
 Take
1 letter from each word; how many different
arrangements?
THE
CAT
Two Traits


If A = tall; a = short & B = blue; b = white
What is the phenotype of:
 AaBB
 aabb
 AAbb
 aaBb
Dihybrid Crosses:


Dihybrid = an individual that is heterozygous for
two traits
Example: AaBb
Dihybrid Crosses

Consider two genes in peas:
 Pea
color: Y (yellow) & y (green)
 Pea shape: R (round) & r (wrinkled)



Parent genotype: YyRr
Parent phenotype: yellow & round
What gametes will this parent make?
 REMEMBER:
each gene
 YR, Yr, yR, yr
the gametes must contain one allele for
Dihybrid Crosses;
Y=yellow y=green; R = round r = wrinkled


Practice Cross: YyRr x YyRr
Gametes from each parent: YR, Yr, yR, yr
YR
Yr
yR
yr
YR
YYRR
YYRr
YrRR
YyRr
Yr
YYRr
YYrr
YyRr
Yyrr
yR
YyRR
YyRr
yyRR
yyRr
yr
YyRr
Yyrr
yyRr
yyrr
Dihybrid Crosses;
Y=yellow y=green; R = round r = wrinkled

How many genotypes are…
 Yellow
& round: 9
 Yellow & wrinkled: 3
 Green & round: 3
 Green & wrinkled:

Phenotypic ratio?
Dihybrid Crosses


Two dihybrid parents will always make a
phenotypic ratio…
Dom, Dom : Dom, rec : rec, Dom : rec, rec
9
:
3 :
3
:
1
Dihybrid Crosses – Let’s Practice




L = long fur; l = short fur
P = polka dots; p = solid color
Parents: LlPp x LlPp
What proportion of offspring will have…
 Long,
polka dotted fur?
 Long, solid fur?
 Short, polka dotted fur?
 Short, solid fur?
Other two trait crosses

TtPP x TTPP – NOT dihybrid
Gametes from Parent #1: TP, tP
 Gametes from Parents #2: Tp
 Possible genotypes & phenotypes of the offspring?


A male rabbit with the genotype GGbb is crossed with
a female rabbit with the genotype ggBb. Determine
the phenotypes and proportions in the offspring.
How many out of
 How many out of
 How many out of
 How many out of

16 have grey fur & black eyes?
16 have grey fur & red eyes?
16 have white fur & black eyes?
16 have white fur & red eyes?