Transcript Mendel and Punnett Notes

Gregor Mendel’s Peas
• Gregor Mendel’s Peas
– Genetics is the scientific
study of heredity.
• Gregor Mendel was an
Austrian monk.
• Mendel studied garden peas
Gregor Mendel’s Peas
–Mendel knew that
– the male part of each
flower produces pollen,
(containing sperm).
– the female part of the
flower produces egg
cells.
– Together they make a
new plant
Gregor Mendel’s Peas
• Pea flowers are self-pollinating. (Pollen can fertilize
the flower it was made on)
• Self-pollination results in the offspring getting all its
DNA from 1 organism.
Gregor Mendel’s Peas
• Mendel used True-Breeding Pea plants
– Plants that were homozygous for a trait
• To prevent Self pollination- Mendel
removed either the male or the female parts
from each flower.
Gregor Mendel’s Peas
• Mendel took a
brush and crosspollinated the
flowers by hand!
• Mendel was able
to produce seeds
that had two
different parents.
Genes and Dominance
• Genes and Dominance
– A trait is a specific characteristic that varies from
one individual to another.
Genes and Dominance
• Each original pair of plants is the P (parental)
generation.
• The offspring are called the F1, or “first filial,”
generation.
• The offspring of crosses between parents with
different traits are called hybrids.
• The F1 hybrid plants all had the character of only
one of the parents.
Genes and Dominance
• Genes and Dominance
• Mendel studied seven pea plant traits, each with
two contrasting characters.
• He crossed plants with each of the seven
contrasting characters and studied their offspring.
Genes and Dominance
Mendel’s F1 Crosses on Pea Plants
Genes and Dominance
Mendel’s Seven F1 Crosses on Pea Plants
Mendel’s F1 Crosses on Pea Plants
Genes and Dominance
• Mendel's first conclusion was that biological
inheritance is determined by factors that are passed
from one generation to the next.
• We call these factors GENES
Genes and Dominance
• Mendel luckily chose traits controlled by a single
gene with different forms.
• The different forms of a gene are called
alleles(ah-le-eels).
GENOTYPE vs PHENOTYPE
• GENOTYPE – are the actual DNA coded
genes or instructions that make you.
• PHENOTYPE – The express or what the
genotype looks like in the physical world.
For short – What you look like.
Genes and Dominance
– The principle of dominance states that some
alleles are dominant and others are recessive.
Genes and Dominance
• Dominant alleles – Only need one for this
form to show in the phenotype
Possible Genotype – (DD or Dr)
• Recessive – Need two alleles for this one to
show in the phenotype
Possible Genotype– (rr)
Segregation
• Segregation
– Mendel crossed the F1 generation with itself to
produce the F2 (second filial) generation.
– The traits controlled by recessive alleles
reappeared in one fourth of the F2 plants.
Segregation
• The reappearance of the trait controlled by
the recessive allele indicated that at some
point the allele for shortness had been
separated, or segregated, from the allele for
tallness.
Segregation
• During the formation of GAMETES (sex
cells) – Alleles are separated (segregated)
into different resulting daughter cells.
Segregation
• Alleles separate during gamete formation.
Using a Punnett
Square
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
What is a PUNNETT SQUARE?
• Letters stand for dominant and
recessive alleles
• An uppercase letter stands for a
dominant allele
• Lowercase letters stand for recessive
alleles
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:
Using a PUNNETT SQUARE
Now you need two parents to mate,
ones with a known genotype
For example, a red flower
(genotype Rr) and a white flower
(genotype rr). Rr x rr
Using a PUNNETT SQUARE
Place one of the parents on top, and
one on the left. You should get a
something similar to this:
Using a PUNNETT SQUARE
Finally, take each letter in each column and
combine it with each letter from each row in
the corresponding square. You should now
have a picture close to this:
Using a PUNNETT SQUARE
• The two-letter combinations are the
possible genotypes of offspring
• They are: Rr, Rr, rr, and rr
genotypes
• From this it is possible to determine
the probability (chance) that a flower
will have a red phenotype (2/4 or
50%) or a white phenotype (2/4 or
50%)