Transcript CHAPTER 9 MENDEL

GREGOR MENDEL 1822-1884
• The monk who worked with?
MENDEL’S GOAL
• EXPLAIN the PATTERN of HEREDITY
from PARENT to OFFSPRING
WHY PEA PLANTS?
•
•
•
•
•
EASY to GROW
REPRODUCE offspring in a SHORT TIME
Get offspring results quickly
Only 7 traits (genes)
Each TRAIT HAS 2 FORMS (physical)
– Avoid any confusion in results
• MALE & FEMALE parts on flowers allow for
– SELF-FERTILIZATION OR MENDEL could
control breeding with CROSS FERTILIZING
HOW MENDEL CROSS FERTILIZED
FLOWERS & THEIR PARTS
Male flower
parts
Female
flower parts
MENDEL’S FIRST TRAIT
EXPERIMENT- Flower Color
• Two purebred parents are
crossed
• One parent has PP it has
purple flowers
• The other has pp white flowers
• The offspring are all purple.
Because they have one
dominant gene P.
White recessive
offspring
Purple
Dominant
Mendel’s Discovery HW
assignment
Breeding Pea Color
MENDEL’S OBSERVATIONS OF
OF 1ST PURE-BRED CROSS
• The PARENT’s generation uses the code P.
• They are PUREBRED plants. They had 2 genes that
were both represented by the same letters, either PP for
purple flowers or pp for white flower color.
• The OFFSPRING generation uses the code F-1
• offspring are Heterozygous, Pp. They have 2 genes,
one dominant and one recessive.
MENDEL’S OBSERVATIONS OF 1ST
PURE-BRED CROSS
• ALL OFFSPRING had DOMINANT, purple flowers
• None had the white flowers, or Recessive trait.
MENDEL’S 2ND EXPERIMENT
SELF-FERTILIZATION CROSS
• He bred the F-1GENERATION
• Remember the F-1 were HYBRIDS, Pp
– They had two genes, one dominant and one
recessive.
• Mendel did not realize this. He saw purple
flowers. So he expected to see?
• All purple offspring
F-2 RESULTS
• Some PURPLE & also some White flowered plants
appear
• HOW WAS THIS POSSIBLE?!
• THE RECESSIVE TRAIT was always there in the genes
of the flowers.
• To get a white flower two recessive genes had to come
together in an offspring to show up. pp
• The phenotype ratio of offspring he had by flower color
was 3:1 Three purple to one white.
• The genotype ratio he got was 1 PP, 2Pp, 1 pp
it is written at 1:2:1
Mendel’s 1st exp.
Mendel’s 2nd
experiment
Crosses
purebreds
Crosses
hybrids
Law of Dominance & Recessive Traits
• Some traits are
dominant over others
• Some traits may not
be expressed unless
inherited on both
genes
Principle of Segregation
• For any trait, the pair of alleles from each parent
separate and only one allele passes from each parent on
to an offspring. Which allele is inherited is a due to
chance.
PRINCIPLE OF INDEPENDENT ASSORTMENT
• different pairs of alleles
are passed to offspring
independently of each
other (during meiosis and
fertilization)
• Some offspring may not
resemble their parents.
PROBABILITY
http://nortonbooks.com/college/biology/animations/ch10a05.htm
•
•
•
•
•
•
•
• ABILITY TO PREDICT FUTURE EVENT
PREDICT THE FREQUENCY OF OFFSPRING TRAITS
EXAMPLE A COIN TOSS
WHAT are the CHANCES of GETTING HEADS with 1
COIN?
½, one side is heads, the other is tails
WHAT are the CHANCES of getting HEADS with 2
COINS?
½ x ½ =?
¼!
2 trait cross-dihybrid
Cross a homozygous X recessive
Gamete combos from each parent are only
RY or ry
F-1 generation
All are
heterozygous
genotypes
Cross of the F-1 offspring hybrids
DI-HYBRID CROSSES
Use your Worksheet Di-hybrid Crosses
If you need help, go to this tutorial