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Set up today’s page in your journal…
• Page: 44• Title: Mendelian Genetics• Date: 11-18-14• Essential Question: Can genetic outcomes
be predicted with 100% accuracy?**Do NOT leave a summary space on the first page! We will be using multiple pages
today.**
Principle of Dominance: some alleles are dominant and others are recessive
Y = Dominanty = Recessive
• the dominant allele will always be expressed when it is present
• a capital letter is used to represent a dominant allele[
[
Inheritance is determined by biological factors that are passed from one generation to the next.
In other words, which traits you pass on depends on what genes
you get from your parents.
Genes: chemical factors that determine traits
(small sections of your DNA strand…remember??)
Alleles: different forms of a gene
Principle of Dominance: some alleles are dominant and others are recessive
Y = Dominanty = Recessive
• the dominant allele will always be expressed when it is present
• a capital letter is used to represent a dominant allele
Y = Dominanty = Recessive
• the recessive allele will only be expressed when the dominant is not present
• a lowercase letter is used to represent a recessive allele
Phenotype: appearance
Genotype: the actual genes
*Two organisms can have the same phenotype but
different genotypes*
BB Bb bb
Brown Eyes vs Blue eyes
Principle of Independent Assortment: the way alleles separate during meiosis is completely random and cannot be
predicted
**This is why you never know for
sure which traits will be passed on
to which offspring!**
Probability: the likelihood that a
particular event will occur
We can predict possible genetic outcomes using
probability.
• The letters in the Punnett square
represent alleles passed on from parent
to child.
Punnett squares are used to predict and
compare the genetic variations that will result from a cross.
1st Step = Identify the trait and what letter will represent it
What would be the possible outcomes for the offspring of a cross between pink flower (PP) and a
white flower (pp)?
“P” and “p”
How to complete a Punnett Square
2nd Step = Assign the dominant/recessive trait for your letters
What would be the possible outcomes for the offspring of a cross between pink flower (PP) and a white flower (pp)?
P = PINK (dominant) p = WHITE (recessive)
How to complete a Punnett Square
3RD Step = Match the letters to the correct parent (if none are specified, assume the
FIRST one is dad)
What would be the possible outcomes for the offspring of a cross between pink flower (PP) and a
white flower (pp)?
= PP = ppMOMDAD
How to complete a Punnett Square
Let’s sum it up…..1st = Identify the trait and what letter will represent it
2nd = Assign the dominant/recessive trait for your letters
3rd = Match the letters to the correct parent
4th = Now fill in your Punnett square
Punnett Square practice…1. What would be the possible outcomes for the offspring of a cross between pink flower (PP) and a white flower (pp)?
P P
p
p
Pp Pp
Pp Pp
P = Pink p = White
DAD = PPMOM = pp
**When using the letters like “P and p” OR “C and c”, draw the lowercase letter in cursive or just make sure you make them look different. Otherwise, you might
confuse the dominant for the recessive **
2. Long fingers are dominant (F) to short fingers (f). Complete the Punnett square for a homozygous
recessive mom and a heterozygous dominant dad.
F f
f
f
Ff ff
Ff ff
F = Longf = Short
DAD = FfMOM = ff
3. In a plant, long stems are dominant (L) to short stems (l). If a homozygous dominant flower and a homozygous recessive
plant are crossed, what would be the phenotypic ratio of their offspring?
L L
l
l
Ll Ll
Ll Ll
L = LongL = Short
DAD = LLMOM = ll
4. Straight hair (C) is dominant to curly hair (c). What would be the probability that a child would have curly
hair if both parents are heterozygous dominant?
C c
C
c
CC Cc
Cc cc
C = Straightc = Curly
DAD = CcMOM = Cc
5. Having a hitchhiker's thumb is a dominant trait (T). If a woman with a straight thumb has a child with a man who is heterozygous for the trait, what are the chances
their child will have a hitchhiker's thumb?
T t
t
t
Tt tt
Tt tt
T = Hitchhikert = Straight
DAD = TtMOM = tt
6. What would the phenotypic and genotypic ratios be for two purple (Pp) flowers that were bred together?
P p
P
p
PP Pp
Pp pp
P = Purplep = White
DAD = PpMOM = Pp
Can you identify your own genotypes and phenotypes?
Hairline:
Widow’s peak is dominant tostraight hairline
Eye Shape:
Almond eyes is dominant to round eyes
Tongue Rolling:
CAN roll the tongueis dominant to cannot
Eyelash Length:
Long eyelashes is dominant toshort eyelashes