Download Mendelian Genetics

JIGSAW
• You will have five minutes to master your set
of notes as YOU will be teaching the class
your set!
• Take paper with you to your station so you can
read, summarize and record the notes from
your section.
• We will then come together as a class to
discuss MENDELIAN GENETICS as
understood by YOU!! 
• Best teaching group will receive bonus points
on their lowest daily grade…..
Mendelian Genetics
The Work of Gregor Mendel
Chapter 11.1
What is Inheritance?
• Every living thing has a set of
characteristics passed on to them from their
parents – genes!
• Genetics: The scientific study of heredity
Gregor Mendel
• 19th century Austrian monk
• Worked in monastery
garden with pea plants
“Father of Genetics”
Some terms to know…
• Fertilization: male and female reproductive cells
join to form a new cell – diploid embryo
• Self-pollinating plants: sperm cells (in pollen)
fertilize the egg cells in the same flower
• True-breeding: if plant self-pollinates, offspring
produced is identical to itself
Mendel’s Work
• Prior Knowledge
– Part of each flower produces pollen (male
sperm) and part produces egg cells (female)
– Pea flowers are normally self-pollinating
– His peas were true-breeding (tall plants
produce tall plants, short plants produce short
plants, green seeds produce green
seeds…etc)
Mendel’s Work
• Mendel’s Plan:
– To produce seeds by joining male and female
reproductive cells from two different plants
– To do this, self-pollination needed to be
prevented
– So, he cut away pollen parts from one plant and
dusted them on a different flower (Crosspollination)
NOW, seeds produced have two different parents:
He could now cross-breed plants with different
characteristics and study the results…
Traits
• Mendel studied seven
different pea plant
traits
• Trait: Specific
characteristic that
varies from one
individual to another
Ex. Seed color or plant
height
Mendel’s F1 Crosses on Pea Plants
• P (Parental generation)
– Original pair of plants
• F (Filial generation)
– Offspring - “filia” means son/daughter
– F1 is the first generation of offspring (from
P generation parents)
• Hybrid = offspring of crosses between
parents with different traits
Examples of hybrid crosses
• When one parent’s pod color was green
and the other parent’s pod color was
yellow, the offspring was…green.
• When one parent was round and one
parent’s seed was wrinkled, the
offspring was…round.
Did the characteristics of the parent
plants blend in the offspring?
• NOT AT ALL!
• ***Each offspring carried on the character
of only ONE parent!
• Green parent x Yellow parent = Green offspring
• Round parent x Wrinkled parent = Round offspring
WHY?
• What conclusions can you make?
Mendel’s Principles
• Principle of Biological Inheritance
(unit characters)
• Principle of Dominance
• Principle of Segregation
• Principle of Independent Assortment
KNOW THESE FROM PAGE 272!!!!!!!!!!!
Mendel’s 1st Conclusion
• Biological inheritance is determined by
factors that are passed from one generation
to the next
– GENES - chemical factors that determine traits
– ALLELES - different forms of a gene
• Ex: The gene for plant height occurs in one form that
produces tall plants and in another, short plants – twp
alleles
Mendel’s 2nd Conclusion
• Principle of DOMINANCE
– States that some alleles are dominant and
some are recessive
– Let’s look at our example:
• When one parent’s pod color was green
and the other parent’s pod color was
yellow, the offspring was…green.
Which color is DOMINANT?
Dominance
• An organism with a dominant allele for a
form of a trait will always exhibit that form
of the trait
• An organism with a recessive allele for a
form of a trait will only exhibit that form
when the dominant allele is not present
Gene Expression
•
•
Each form of the particular gene is an
allele.
Alleles can be either
1. Dominant – always show trait - T
2. Recessive – only see if dominant trait absent – t
•
In order to see the trait expressed, 2
alleles must be paired together (one from
mom and one from dad)
T
+
t
Tt
Mendel’s 3rd Conclusion
• Had the recessive alleles totally disappeared or
were they still present in the offspring?
P: Green parent x Yellow parent
F1: Green offspring  do they still have recessive
alleles?
• Mendel allowed the F1 hybrid plants to selfpollinate
– He crossed the F1 generation with itself to produce
the F2
F1: Green offspring x Green offspring
F2: ???
Results….
• Instead of all green…he saw YELLOW too!
Even though the plants are both green,
they can have a yellow baby because
the allele is still present!
F1
gametes
F2
Gg
G
GG
Gg
g
G
g
Gg
Gg
gg
 Segregation
Results of F1 Cross
• Mendel assumed dominant masked the
recessive allele
• But, recessive alleles reappeared in F2!
Example –
P: Green parent x Yellow parent
F1: Green offspring x itself
F2: Green offspring and Yellow offspring
• Somehow the alleles for green and yellow
had separated – Segregation!!!!!
– Occurs during formation of gametes
Principle of Segregation
As gametes form, gene pairs
(homologous chromosomes) separate.
Each gamete contains one gene for the
trait.
When do gametes form?
So when does segregation occur?
“Mendel’s Principle of Segregation”:
•
Recessive characters hidden in the F1 progeny of two
true-breeding strains, reappear in a specific
proportion of the F2 progeny.
Segregation
Segregation
Homologous pairs separate!
ANAPHASE!!
Principle of
Independent Assortment
As gametes form,
gene pairs separate
independently of each other.
Alignment of one chromosome pair
during metaphase, does not affect
alignment of another pair.
Random arrangement creates
independent assortment = VARIATION!
Independent Assortment
Genetic variation results since gametes carry different genes.
Independent Assortment
• Each plant in the F1 generation was formed
by the fusion of a gamete carrying the
dominant alleles (RY) with another gamete
carrying the recessive (ry) alleles.
• Does this mean the two dominant alleles
would always stay together?
• Or would they “segregate independently”
so that any combination of alleles was
possible?
Principle of Independent
Assortment
Genes for different traits can segregate
independently during the formation of
gametes.
Example: genes for seed shape segregate
independently of those for seed color