Gregor Mendel's historic discovery and experiments. How Punett Squares work Explanation of the differences between chromosomes, genes, and alleles. Definitions of vocabulary words.

1. © Fall 2005, Pflugerville ISD, 7th Grade
GENETICS NOTES
• Gregor Mendel’s story
• How Punett Squares work
• Explanation of the differences between
chromosomes, genes, and alleles.
• Definitions of genetic vocabulary words

2. © Fall 2005, Pflugerville ISD, 7th Grade
Gregor Johann Mendel
Austrian monk
Studied the
inheritance of traits in
pea plants
Developed the laws of
inheritance
Mendel's work was
not recognized until
the 1800s
Now he’s called the
father of genetics.
2

3. © Fall 2005, Pflugerville ISD, 7th Grade
Gregor Johann Mendel
Between 1856 and
1863, Mendel
cultivated and tested
thousands of pea plants
He discovered how
heredity works – how
organisms transfer their
traits to their offspring.
copyright cmassengale 3

4. © Fall 2005, Pflugerville ISD, 7th Grade
copyright cmassengale
4
Mendel stated that
physical traits are
inherited as “particles”
Mendel did not know
that the “particles” were
actually Chromosomes –
DNA!
Particulate Inheritance

5. © Fall 2005, Pflugerville ISD, 7th Grade
Why peas, Pisum sativum?
Why Peas?
Produce lots of
offspring
Grow quickly
Can be grown in a small
area
Can be artificially cross-
pollinated
copyright cmassengale 5

6. © Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
• Mendel tested 7 traits:
1. Flower color
2. Flower position
3. Seed color
4. Seed shape
5. Pod shape
6. Pod color
7. Plant height
http://www.fieldmuseum.org/exhibits/traveling_mendel.htm
p173 Life Science Textbook

7. © Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
http://biology.kenyon.edu/courses/biol114/KH_lecture_images/Mendel/Mendel.html
What
color do
you
predict?
What
color do
you
predict?
What
color do
you
predict?
What
color do
you
predict?
What
color do
you
predict?
What
color do
you
predict?
What
color do
you
predict?
What
color do
you
predict?

8. © Fall 2005, Pflugerville ISD, 7th Grade
Results of Mendel’s 1st part of his
experiment. (Copy drawing on the left)
• The first
generation (F1) of
plants all had
purple flowers.
• Where did the
white color go??
(Pp) (Pp)
(Pp) (Pp)
Purple Parent (PP)
White
Parent
(pp)

9. © Fall 2005, Pflugerville ISD, 7th Grade
• Mendel crossed his first
generation (F1 x F1)
purple flowered plants
together.
• In the second
generation (F2) he had
3 purple flowered
plants, and 1 white
flowered plant.
(PP) (Pp)
(Pp) (pp)
Purple Parent (Pp)
Purple
Parent
(Pp)
Results of Mendel’s 2nd part of his
experiment. (Copy drawing on the left)

10. © Fall 2005, Pflugerville ISD, 7th Grade
Mendel’s Conclusions:
• Mendel noticed in the first generation, all
of the white flowers seemed to
disappear.
• He called this a recessive trait.
• The white color faded away, and was not
expressed physically.
• But - it showed up in the next
generation!

11. © Fall 2005, Pflugerville ISD, 7th Grade
Mendel’s Conclusions:
• The purple that overpowered the recessive
color was named the dominant trait.
• Mendel found that each plant carried two
sets of instructions for each trait (one from
the “mom” and one from the “dad”).
• These sets of instructions are called alleles.

12. © Fall 2005, Pflugerville ISD, 7th Grade
Copy the Pedigree of the two peas
and their offspring on the left.

13. © Fall 2005, Pflugerville ISD, 7th Grade
Vocabulary
• Recessive trait- a trait that shows up
only when two recessive alleles for the
same characteristic are inherited
• Dominant trait- Represented with a
capital letter, it overpowers the recessive
trait.
• Genes- a section of DNA that carries
hereditary instructions and is passed
from parent to offspring
• Alleles- multiple forms of the same gene

14. © Fall 2005, Pflugerville ISD, 7th Grade
All the DNA that codes
for how to build you
Separated into bundles
called chromosomes
Humans have 23 pairs of homologous chromosomes.

15. © Fall 2005, Pflugerville ISD, 7th Grade
Eye Color Blue Brown Brown Eyes
Tall Tall
Red Brown
Each chromosome
has sections on it
called genes
There are 3 genes
shown on this slide

16. © Fall 2005, Pflugerville ISD, 7th Grade
Unit A : Chapter 1 : Section 1

17. © Fall 2005, Pflugerville ISD, 7th Grade
Unit A : Chapter 1 : Section 1

18. © Fall 2005, Pflugerville ISD, 7th Grade
Each chromosome
has sections on it
called genes
Eye Color Blue Brown
Tall Tall
Red Brown
One allele
from mom
One allele
from dad
What color are
mom’s eyes?
What color are
Dad’s eyes?
What color are
baby’s eyes?
Phenotype of
the baby is:
There are 3 genes
shown on this slide
alleles are ½ of a gene
Brown Eyes

19. © Fall 2005, Pflugerville ISD, 7th Grade
Vocabulary
• Heredity- the passing of traits from
parent to offspring.
• Homozygous – both alleles are identical.
Also known as True-breeding. Ex: PP or
pp
• Heterozygous - each allele is different.
Also known as hybrids. Ex: Pp

20. © Fall 2005, Pflugerville ISD, 7th Grade
Vocabulary
• P generation- the parent generation.
• First-generation or F1- the very first set of
offspring from two parents
• Second-generation or F2 – the offspring of
the kids from the F1 generation (grandkids)

21. © Fall 2005, Pflugerville ISD, 7th Grade
Vocabulary
Genotype- the genetic code. Ex: Pp
Phenotype- the physical appearance. Ex:
Purple Flowers
Pedigree – your family tree.
Incomplete Dominance – a blend of the
parents’ phenotypes.
Ex: Bb light brown
brown white

22. © Fall 2005, Pflugerville ISD, 7th Grade
Vocabulary
Codominance – When both phenotypes are
visible. Ex: Hair that has both blond strands
and brown strands.
Karyotype – a chart of all your
chromosomes lined up in order.
Sex Chromosomes – chromosomes that
determine a person’s gender. ex: XX and XY
X-linked, or sex-linked inheritance – see
p186 in Life Science Book.

23. © Fall 2005, Pflugerville ISD, 7th Grade
Let’s Review
1. If you crossed a true-breeding black
rabbit with a true-breeding white
rabbit, all of the offspring would be
black. Which trait is dominant in
rabbits: black fur or white fur?
2. Which trait is recessive?

24. © Fall 2005, Pflugerville ISD, 7th Grade
Answer
• The trait for black
fur is dominant
over the trait for
white fur. The
white fur trait is
recessive.
http://www.buckeyevalleyfarms.freeservers.com/photo.html
(Bb) (Bb)
(Bb) (Bb)
Black Rabbit (BB)
White
Rabbit
(bb)

25. © Fall 2005, Pflugerville ISD, 7th Grade
Google’s tribute to Mendel
July 2011

26. © Fall 2005, Pflugerville ISD, 7th Grade
Science Humor