1. What exactly are Chromosomes,
DNA and Genes?
Introduction to Genetics

2. Introduction to Genetics Video

3. Chromosome
• 46 inside every cell
• Chromosomes are in
the cell in pairs. Dad’s Chromosome Mom’s Chromosome
• One came from mom and one came from dad.

4. DNA - deoxyribonucleic (say: dee-ox-
see-ri-bo-nyoo-clay-ik) acid
• Long strands of genetic code
• Makes up chromosomes in plants and animals
DNA

5. Genes
• Tiny pieces of DNA that are instructions for
specific traits

6. Traits
• Things that you inherit from your parents
• Examples: Hair color, eye color and having
freckles or not
• Through sexual reproduction you inherited a set
of traits

7. Traits
• Pairs of letters are used to define genes in your
body
• CAPTIAL LETTERS are used to represent
DOMINANT genes
• lower case letters are used to represent recessive
genes
• Dominant trait: If you receive even one of these
in the pair, you will get a specific trait.
• Recessive trait: You have to have two of these in
the pair to get a specific trait

9. Genotypes
• The letter associated with the gene
▫ Example: W (dominant widow’s peak) w (recessive no
widow’s peak)

10. Phenotypes
• This is the "outward, physical manifestation“
• The actual physical trait
▫ Example: You have a widow’s peak.

11. Allele
• Allele: The single letter such as the a or the A.

12. Heterozygous – having two different
alleles
• AA
• bb

13. Homozygous – having the same alleles
• Aa
• Bb

14. Purebred or Hybrid?
• Purebred: AA or aa
• Hybrid: Aa

15. Practice:
B – brown hair b – red hair
My genes: Bb
What color hair will I have?
Is Bb the phenotype or the genotype?
Are my genes heterozygous or
homozygous?

16. Practice:
A – attached earlobe a – unattached earlobe
My genes: aa
What will my earlobes do?
Is attached earlobe the phenotype or the
genotype?
Is my genotype homozygous or
heterozygous?

17. Practice:
D – dimples d – no dimples
My genes: DD
Do I have dimples or not?
What is the genotype?
Is my genotype heterozygous or
homozygous?

18. Quiz
F – freckles f – no freckles
My genes: FF
Do I have freckles or not?
What is the phenotype?
What is the genotype?
Is my genotype heterozygous or homozygous?
Which parent carried the dominant gene?

19. Mom Dad has
has brown eyes
blue (BB or Bb)
eyes Therefore, Dad must
(bb) have the Bb genotype,
because he must have
given her the “b” allele.
Daughter His “b” allele is masked
by his “B”/dominant
has allele.

20. What is a PUNNETT SQUARE?
• A tool to predict the probability of certain
traits in offspring that shows the different
ways alleles can combine
• A way to show
phenotype & genotype
• A chart that shows
all the possible
combinations of alleles
that can result when
genes are crossed

21. Punnett Squares Video

22. Using a PUNNETT SQUARE
To set up a Punnett square, draw a large
square, and then divide it into 4 equal
sections (also squares). It should look
something like this:

23. Using a PUNNETT SQUARE
• Now you need two parents to mate, ones with
a known genotype
• For example, Brown hair (genotype BB) and
blonde hair (genotype Bb). BB x Bb
• In this scenario, the Mom has brown hair.
The dad blonde hair.

24. Using a PUNNETT SQUARE
Place one of the parents on top, and one on the
left. You should get a something similar to
this:
B b
B
B

25. Using a PUNNETT SQUARE
• The two-letter combinations are the possible
genotypes of offspring
• They are: BB, Bb, BB, and Bb genotypes
• From this it is possible to determine the
probability (chance) that a baby will have a
brown phenotype (2/4 or 50%) or a blonde
phenotype (2/4 or 50%)

26. Does it work with animals and plants?
• Yes, all of this works the same way in
determining the outcome of combining animals
and plants.
•How can we relate this to
selective breeding?
•How can we relate this to
genetic engineering?