Transcript Dihybrid Crosses

Ashley, Alyssa, Sydney & Mallory
March 13, 2012
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Allele- A specific form of one gene
Punnett Square- Notation for helping to work out
possible genotypes and phenotypes in a cross
Heterozygous- Having two different alleles but
the same gene (Tt)
Homozygous- Having two identical alleles with
the same gene (TT or tt)
Gamete- A mature sexual reproductive cell that
unites with another cell to form a new organism
Phenotype- Physical characteristics of an
organism
Genotype- The alleles of an organism, written
with uppercase and lowercase letters
Draw and solve
this punnett square
in your notes.
GENOTYPE!
GENOTYPE!
Tt
Tt
tt
tt
GENOTYPE!
GENOTYPE!
Tt- Tall (50%)
Phenotypes: tt- Short (50%)
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The study of inheritance patterns for
organisms differing in two traits (In simple
words a more complicated punnett square)
Gregor Mendel invented dihybrid crosses
while trying to figure out the different traits
of pea plants
http://www.siskiyous.edu/class/bio1/genetics/di
hybrid_v2.html
Straight Hair
Dimples
hh
Dd
Wavy Hair
No Dimples
Hh
dd
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Step 1: List the genotypes (HhDd: Hhdd:
hhDd: hhdd)
Step 2: Make a ratio of the genotype. (4:4:4:4)
Step 3: Simplify ratios. (1:1:1:1)
Step 4: List the phenotypes. (Wavy/Dimples:
Wavy/No dimples: Straight/Dimples: Straight/
No Dimples)
Step 5: Make a ratio for the phenotype.
(1:1:1:1)
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Autosomes are all
chromosomes which are
not sex chromosomes.
(Example: Humans have
22 pairs of autosomes
and 2 sex
chromosomes)
Sex Chromosomes
determine the sex of an
individual. (Example:
Females have XX and
males have XY sex
chromosomes)
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Crossing over between non-sister chromatids
of a homologous pair in Prophase I can result
in an exchange of alleles.
The effect of crossing over is that the
resulting variation is almost indefinite.
Kourtney=brown eyes, wavy hair; Scott= blue eyes,
straight hair
Beyonce=normal lips, dark brown hair; Jay-Z= broad
lips, black hair
Morgan=short, wavy hair; Thomas=tall, straight hair
Boy
Girl
Alexis=dimples, attached earlobes; Justin=no
dimples attached earlobes
Girl
Boy