7th grade lesson on Punnett Squares and Genetics

1. QOD
1. THE SHAPE OF DNA IS DESCRIBED AS A _____ _____.
2. A GENE IS A SEGMENT OF _____ THAT CORRESPONDS TO A PARTICULAR _____.
3. A CELL WITH ONLY 1 KIND OF EACH CHROMOSOME IS _____; A CELL WITH 2
KINDS OF EACH CHROMOSOME IS _____.
4. A PUNNETT SQUARE DETERMINES THE POSSIBLE COMBINATIONS OF _____.
5. _____ IS WHAT MENDEL CALLED HOMOZYGOUS.
6. CHROMOSOMES ARE MADE WHEN STRANDS OF _____ COIL AROUND _____.

2. Essential Question
How can I predict the genotype of
an offspring?

3. In Glossary
Heredity The passing of traits from parent to
offspring.
alleles
Dominant Traits
Recessive Traits
Genotype
Phenotype
Punnett Square

4. In Glossary
Heredity The passing of traits from parent to
offspring.
alleles Different forms of a trait that make up a
gene pair.
Dominant Traits
Recessive Traits
Genotype
Phenotype
Punnett Square

5. In Glossary
Heredity The passing of traits from parent to
offspring.
alleles Different forms of a trait that make up a
gene pair.
Dominant Traits A trait that covers over, or dominates,
another form of that trait.
Recessive Traits
Genotype
Phenotype
Punnett Square

6. In Glossary
Heredity The passing of traits from parent to
offspring.
alleles Different forms of a trait that make up a
gene pair.
Dominant Traits A trait that covers over, or dominates,
another form of that trait.
Recessive Traits The trait that is covered over of
dominated , by another trait and seems to
disappear.
Genotype
Phenotype
Punnett Square

7. In Glossary
Heredity The passing of traits from parent to
offspring.
alleles Different forms of a trait that make up a
gene pair.
Dominant Traits A trait that covers over, or dominates,
another form of that trait.
Recessive Traits The trait that is covered over of
dominated , by another trait and seems to
disappear.
Genotype Genetic make up of an organism.
Phenotype
Punnett Square

8. In Glossary
Heredity The passing of traits from parent to
offspring.
alleles Different forms of a trait that make up a
gene pair.
Dominant Traits A trait that covers over, or dominates,
another form of that trait.
Recessive Traits The trait that is covered over of
dominated , by another trait and seems to
disappear.
Genotype Genetic make up of an organism.
Phenotype The way an organism looks and behaves.
(blue eyes, brown hair)
Punnett Square

9. In Glossary
Heredity The passing of traits from parent to
offspring.
alleles Different forms of a trait that make up a
gene pair.
Dominant Traits A trait that covers over, or dominates,
another form of that trait.
Recessive Traits The trait that is covered over of
dominated , by another trait and seems to
disappear.
Genotype Genetic make up of an organism.
Phenotype The way an organism looks and behaves.
(blue eyes, brown hair)
Punnett Square A tool used by Gregory Mendel to predict
the genetic make up of an offspring.

10. Nucleotides
Adenine-Thymine
Guanine-Cytosine
Chargaff's Ratios.
Erwin Chargaff found that in DNA, the ratios of adenine (A)
to thymine (T) and guanine (G) to cytosine (C) are equal. This
parity is obvious in the final DNA structure.

11. Double Helix

12. DNA complementary
ATCGAATTGA
TAGCTTAACT
CGAATGGCCTGA
GCTTACCGGACT
TTACCGGTCGA
AATGGCCAGCT

13. Adenine
Guanine
Thymine
Cytocine

14. http://learn.genetics.utah.edu/units/basics/tour/
Tour of Basics

15. What is a genotype?
Heterozygous traits are the result of getting the different gene from
each parent. (called HYBRIDS)
◦ If the traits are different the dominant trait will always determine your looks.
Ex. Genotype = Bb or Tt etc…
Homozygous traits are the result of getting the same gene from each
parent.
◦ Looks are determined by the pair of alleles since they are equal. Ex. Genotype
= BB or bb or TT or tt etc…

16. What is a phenotype?
If T represents tall and t represents short.
◦ Heterozygous genotype (called HYBRIDS) Tt = tall plant
◦ Homozygous dominant genotype TT = tall plant
◦ Homozygous recessive genotype tt = short plant
Phenotype are traits that can be detected with out extreme science. Ex. Ms. Johnson
is tall.

17. Stop and Share
What is the difference between a
genotype and a phenotype?

18. How is a Punnett Square interpreted?
Top = one parent’s genotype
Side = other parent’s genotype
Count how many boxes out of 4 have a
phenotype to determine probability.

19. Let’s try some…
If I cross a TT plant with a tt plant
___ # of tall
___ # of short
___ # of pure tall
___ # of pure short
___ # of hybrid tall

20. Sickle Cell Anemia
A substitution in the order of bases
Sickle cells can not carry oxygen to the body
Sickle-cell disease occurs when a
person inherits two abnormal copies of
the hemoglobin gene, one from each
parent.

21. Let’s try some…
If I cross a Tt plant with a tt plant
___ # of tall
___ # of short
___ # of pure tall
___ # of pure short
___ # of hybrid tall

22. Hemophilia
Blood clotting disorder
excessive bleeding, no clotting
only in males
females are carriers
short life spand

24. Let’s try some…
If I cross a TT plant with a Tt plant,
what are the probably offspring?
___ # of tall
___ # of short
___ # of pure tall
___ # of pure short
___ # of hybrid tall

25. Cystic Fibrosis
mutation in the gene
heavy mucus in lungs
difficulty breathing

26. Pedigree
diagram that shows a history of a trait

27. Stop and Draw
In your spiral draw a Punnett square and describe how it is
organized.
Now, share this with your neighbor and compare your
descriptions.

28. Exit Ticket
If I cross a PP plant with a Pp plant
___ # of purple
___ # of white
___ # of pure purple
___ # of pure white
___ # of hybrid purple