Transcript Genetics The study of heredity

Genetics
The study of heredity
http://cc040.k12.sd.us/PPTS/Intro%20to%20Genetics%20(2003). ppt#266,11,Mendel’s second cross
Gregor Mendel
• Born in 1822 in
Czechoslovakia.
• Became a monk at a
monastery in 1843.
• Taught biology and had
interests in statistics.
• Also studied at the
University of Vienna.
http://kentsimmons.uwinnipeg.ca/cm1504/mendel.htm
Mendel (continued)
• Upon return to the
monastery, he
continued to teach
and work in the
garden.
• Between 1856 – 1863
he grew and tested
over 28,000 pea
plants.
http://www.dnalc.org/view/16160-Gallery-2-Gregor-Mendel-s-Garden-Plot.html
Mendel’s Peas
Trait
Dominant
Recessive
• Easy to grow.
• Easily
identifiable traits.
• Can work with
large numbers of
samples.
http://www.anselm.edu/homepage/jpitocch/genbio/geneticsnot.html
Mendel’s Experiments
•
•
•
•
He first created “pure” generations.
Trait = a characteristic
Mendel studied 7 traits.
He crossed plants of contrasting traits
– Ex: Green pea plants + Yellow pea plants
• The offspring (new plants) were called the
F1 generation.
+
What happens when pure yellow peas
are crossed with pure green peas?
• All of the offspring
were yellow.
• Hybrids = the
offspring from
crossing parents
with contrasting
traits.
All offspring are yellow
hybrids (Yy)
Observations
Pure Yellow
Pure Green
P Generation
P Generation
+
YY
Yy
yy
Yy
Yy
F1 Generation
Yy
What did Mendel Find?
A. Inheritance is determined by factors
passed on from one generation to
another.
• Mendel knew nothing about
chromosomes, genes, or DNA. Why?
– These terms hadn’t been defined yet --or seen!!
What were Mendel’s “factors?”
B. The “factors” are now called GENES.
C. Each gene has different forms called
ALLELES.
1. With the gene coding for pea color, yellow is
one form or allele of the gene – and green is
another allele of the gene.
2. Some alleles are DOMINANT and others are
RECESSIVE.
a. In the case of the peas, which color is Dominant &
which is Recessive???
Another way to show the breeding of a
pea plant with yellow seeds and a pea
plant with green seeds
PUNNETT
SQUARE
Yellow Pea
Green Pea ‘mother’
y
y
Y
Yy
Yy
Y
Yy
Yy
Green seed
color is a
recessive allele,
represented with
a ‘y’
‘father’
Yellow seed color
is a dominant
allele, represented
with a ‘Y’
In all possible
combos of alleles,
the offspring will be
yellow hybrids (Yy)
Mendel’s
He allowed the
F1 generation
to self-pollinate
(breed with
each other) to
produce the F2
generation.
nd
2
Cross
Observations
Hybrid Yellow
Results:
75% chance of having
yellow offspring,
25% chance of having
green offspring
Hybrid Yellow
+
Yy
YY
Yy
Yy
yY
F1
Generation
yy
F2
Generation
Also, 25% chance purebred Yellow (YY),
50% chance Hybrid Yellow (Yy),
25% chance purebred Green (yy).
Another way to show the 2nd crossing
F1 Hybrid ‘mother’
Y
Y
y
YY
Yy
F1 Hybrid
‘father’
y
yY
yy
F2 Generation:
Y Y = purebred yellow
Y y = hybrid yellow
y y = purebred green
- OR -
75% yellow
25% green
Purebred = HOMOZYGOUS; Hybrid = HETEROZYGOUS