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Heredity Notes
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What is inheritance?
What is a gene?
What is an allele?
Why are there two
alleles for every gene?
Name: ______________________________________
Date: ________________Period: _________________
What is inheritance? (Slide 2-5)
 Inheritance: the way ______________ are passed down.
 If a father doesn’t have a leg does that mean his children will be born
without a leg????
 Hundreds of years ago people knew that somehow certain traits would
be passed on to their children.
 Gregor _____________ was the first to predict the outcome of
inheritance. The study of inheritance is _____________.
 Mendel did several different experiments on ___________ plant.
Explain Genes and Alleles. (Slide 6)
 A gene is a specific _______________ of DNA.
 You have ___________ genes that code for the same thing (ex.
Height). Each of those two genes is called an _____________.
 So if something had the genes Aa one allele would be “A” the other
would be “a”).
Why are there two alleles for every gene? (Slide7)
 Because organisms get 2 sets of __________________ one from the
mother and one from the ______________.
What is a phenotype?
Explain Phenotype. (Slide 8)
 It is the ________________ characteristics of the trait.
 In most cases it is what we can “________________”.
 Example: Freckles, _________________, attached earlobes etc.
What is a genotype?
Explain Genotype (Slide 9)
 It is the actual ____________________ that make up the trait.
 In most all cases this is represented by __________ letters.
 Example: AA, Aa, aa
What is a dominant
trait?
What is a Dominant trait?(Slide 10)
 A dominant trait is a trait that _______________ or hides the other trait
of an allele.
 For example, _________________colors in hair usually overshadow
the other allele.
 In this class Dominant will always be represented with a capital letter.
 Example: Say “D” is the allele for black hair and “d” is the allele for
blond. Then if an animal had ____________ then it would have black
hair.
What is a recessive
trait?
What is incomplete
dominance?
What is heterozygous?
What is a Recessive trait? (Slide 11)
 A recessive trait is the trait that is _________________ by the
dominant trait.
 In an animal with Dd for hair color the recessive allele is “d”.
 The animal carries a ______________ for blond hair but you can’t tell
by _______________looking at it.
Explain Incomplete Dominance. (Slide 12)
 Sometime traits do ______________have one clear dominant gene or
one clear ________________ gene
 In incomplete dominance, traits appear to ______________together
 When crossing a ___________ snapdragon with a white snapdragon,
the offspring is pink if________________ dominance occurs
 The heterozygous genotype in incomplete dominance appears
different than either of the homozygous alternatives
 Example: red – pink - white
Explain Heterozygous. (Slide 13)
 This is the term given two _________________alleles.
 For example, ______________ is heterozygous.
 It may contain one gene for _____________eyes (A) from the mother
and one gene for blue(_______) eyes from the father.
What is homozygous?
Explain Homozygous. (Slide 14)
 This is the term given to the two _______________ alleles.
 For example, _______________ or aa
 A person may contain __________ genes for -brown eyes – one from
each parent (AA) or 2 for blue (aa).
What can be used to
predict genotype and
phenotype?
Can an Organisms Genotype or Phenotype be predicted?
 Using genotypic and phenotypic ____________ the ______________
of a specific genotype or phenotype appearing can be determined.
 A ______________Square is used to determine these ratios.
What is a phenotypic
ratio?
Explain Phenotypic and Genotypic Ratios
 Phenotypic Ratios
 Shows ratio of what is _________
 Example: previous Punnett square: the phenotypic ratio is 2:2
 This means that the appearance of the offspring will have a
_________ chance to be of the Dominant trait A, and 50% chance to
be of the _____________ trait a.
What is a genotypic
ratio?




Genotypic Ratios
Shows the potential _______________ make-up of the offspring.
Example: previous Punnett square: the genotype ratio is 0:2:2
Meaning the offspring will not be homozygous AA, 50% chance of
being Heterozygous Aa, and 50% chance of being homozygous aa.
Example
How can we determine
genotypes and
phenotypes using a
Punnett Square?
Angus cattle: coat color, B is dominant, b is recessive and cross a BB cow
with a bb bull.
What is the Phenotypic ratio?
What is the Genotypic Ratio?
Cross a BB cow to a Bb bull. But also, another allele is considered.
 Polled: P is dominant p is recessive
 Cross the BbPp bull with the BBpp homozygous recessive polled cow
 BbPp x BBpp
What is the Phenotypic ratio?
What is the Genotypic Ratio?
Summary: Based on what you now know, how would you explain how heredity works and how traits are
passed on to your future family?
Heredity Activity Sheet
Scientists at Bikini Bottoms have been investigating the genetic makeup of the
organisms in this community. Use the information provided and your knowledge
of genetics to answer each question.
1. For each genotype below, indicate whether it is a heterozygous (He) OR
homozygous (Ho).
TT _____
Bb _____
DD _____
Ff _____
tt _____
dd _____
Dd _____
ff _____
Tt _____
bb _____
BB _____
FF _____
A. Which of the genotypes in #1 would be considered
purebred?______________________
B. Which of the genotypes in #1 would be hybrids?
________________________________
2. Determine the phenotype for each genotype using the information provided about
SpongeBob.
Yellow body color is dominant to blue.
YY _________________ Yy _________________ yy _________________
Square shape is dominant to round.
SS _________________ Ss _________________ ss _________________
3. For each phenotype, give the genotypes that are possible for Patrick.
A tall head (T) is dominant to short (t).
Tall = __________
_____________ Short = __________________________
Pink body color (P) is dominant to yellow (p).
Pink body = ________
__________ Yellow body = _____________________
4. SpongeBob SquarePants recently met SpongeSusie Roundpants at a dance.
SpongeBob is heterozygous for his square shape, but SpongeSusie is round.
Create a Punnett square to show the possibilities that would result if SpongeBob
and SpongeSusie had children. HINT: Read question #2!
A. List the possible genotypes and phenotypes for their children.
B. What are the chances of a child with a square shape? ____ out of
____ or ____%
C. What are the chances of a child with a round shape? ____ out of
____ or ____%
5. Patrick met Patti at the dance. Both of them are heterozygous for their pink body
color, which is dominant over a yellow body color. Create a Punnett square to
show the possibilities that would result if Patrick and Patti had children. HINT:
Read question #3!
A. List the possible genotypes and phenotypes for their children.
B. What are the chances of a child with a pink body? ____ out of ____
or ____%
C. What are the chances of a child with a yellow body? ____ out of
____ or ____%
6. Everyone in Squidward’s family has light blue skin, which is the dominant trait for
body color in his hometown of Squid Valley. His family brags that they are a
“purebred” line. He recently married a nice girl who has light green skin, which is
a recessive trait. Create a Punnett square to show the possibilities that would
result if Squidward and his new bride had children. Use B to represent the
dominant gene and b to represent the recessive gene.
A. List the possible genotypes and phenotypes for their children.
B. What are the chances of a child with light blue skin? ____%
C. What are the chances of a child with light green skin? ____%
D. Would Squidward’s children still be considered purebreds?
Explain!
7. Assume that one of Squidward’s sons, who is heterozygous for the light blue
body color, married a girl that was also heterozygous. Create a Punnett square
to show the possibilities that would result if they had children. Use B to
represent the dominant gene and b to represent the recessive gene.
A. List the possible genotypes and phenotypes for their children.
B. What are the chances of a child with light blue skin? ____%
C. What are the chances of a child with light green skin? ____%
8. Mr. Krabbs and his wife recently had a Lil’ Krabby, but it has not been a happy
occasion for them. Mrs. Krabbs has been upset since she first saw her new baby
who had short eyeballs. She claims that the hospital goofed and mixed up her
baby with someone else’s baby. Mr. Krabbs is homozygous for his tall eyeballs,
while his wife is heterozygous for her tall eyeballs. Some members of her family
have short eyes, which is the recessive trait. Create a Punnett square using T for
the dominant gene and t for the recessive one.
A. List the possible genotypes and phenotypes for their children.
B. Did the hospital make a mistake? Explain your answer.