Transcript Monohybrid Crosses

Monohybrid Crosses
Gregor Mendel
• Austrian monk
who started the
study of genetics
in his monastery’s
garden in the
1860s
• Studied heredity
in garden peas
Why did he study peas?
1. They had a variety of characteristics that
occur in two different forms or
.
Why did he study peas?
1. They had a variety of characteristics that
occur in two different forms or alleles .
Why did he study peas?
1. They had a variety of characteristics that
occur in two different forms or alleles .
Why did he study peas?
Why did he study peas?
2. He could easily control which plants pollinated each
other.
Why did he study peas?
2. He could easily control which plants pollinated each
other.
– Pea plants can
, which is when a
plant’s pollen, which contains the sperm, is used to
fertilize the same plant’s egg. If he wanted pure
breeding plants, he could allow the plants to selfpollinate over many generations.
Why did he study peas?
2. He could easily control which plants pollinated each
other.
– Pea plants can self-pollinate , which is when a
plant’s pollen, which contains the sperm, is used to
fertilize the same plant’s egg. If he wanted pure
breeding plants, he could allow the plants to selfpollinate over many generations.
Why did he study peas?
2. He could easily control which plants pollinated each
other.
– Pea plants can self-pollinate , which is when a
plant’s pollen, which contains the sperm, is used to
fertilize the same plant’s egg. If he wanted pure
breeding plants, he could allow the plants to selfpollinate over many generations.
– Pea plants can also
, which is when
the pollen of one plant is used to fertilize another
plant. He could do this by removing stamens or
male parts of the flowers. He could brush pollen
from one flower to the female parts of another
flower.
Why did he study peas?
2. He could easily control which plants pollinated each
other.
– Pea plants can self-pollinate , which is when a
plant’s pollen, which contains the sperm, is used to
fertilize the same plant’s egg. If he wanted pure
breeding plants, he could allow the plants to selfpollinate over many generations.
– Pea plants can also cross-pollinate , which is when
the pollen of one plant is used to fertilize another
plant. He could do this by removing stamens or
male parts of the flowers. He could brush pollen
from one flower to the female parts of another
flower.
Why did he study peas?
Why did he study peas?
3. Peas produce a lot of offspring quickly, so he
could obtain lots of data quickly.
Why did he study peas?
3. Peas produce a lot of offspring quickly, so he
could obtain lots of data quickly.
– P generation-
Why did he study peas?
3. Peas produce a lot of offspring quickly, so he
could obtain lots of data quickly.
– P generation- 1st generation; parental (p)
generation
Why did he study peas?
3. Peas produce a lot of offspring quickly, so he
could obtain lots of data quickly.
– P generation- 1st generation; parental (p)
generation
– F1 generation-
Why did he study peas?
3. Peas produce a lot of offspring quickly, so he
could obtain lots of data quickly.
– P generation- 1st generation; parental (p)
generation
– F1 generation- The first generation of
offspring
Why did he study peas?
3. Peas produce a lot of offspring quickly, so he
could obtain lots of data quickly.
– P generation- 1st generation; parental (p)
generation
– F1 generation- The first generation of
offspring
• F stands for filial or son.
Why did he study peas?
3. Peas produce a lot of offspring quickly, so he
could obtain lots of data quickly.
– P generation- 1st generation; parental (p)
generation
– F1 generation- The first generation of
offspring
• F stands for filial or son.
–F2 generation-
Why did he study peas?
3. Peas produce a lot of offspring quickly, so he
could obtain lots of data quickly.
– P generation- 1st generation; parental (p)
generation
– F1 generation- The first generation of
offspring
• F stands for filial or son.
–F2 generation- The second generation of
offspring; offspring of the F1 generation
3 Steps of Mendel’s Experiments
1. Produce a true-breeding P generation
Self Pollination
Long stemmed plant
P generation
Long stemmed plant
Self Pollination
Short stemmed plant
Short stemmed plant
P generation
3 Steps of Mendel’s Experiments
2. Producing an F1 generation
C
r
o
s
s
P
o
l
l
i
n
a
t
i
o
n
Long stemmed
F1 Generation
3 Steps of Mendel’s Experiments
3. Producing an F2 Generation
C
r
o
s
s
P
o
l
l
i
n
a
t
i
o
n
¾ Long Stemmed
¼ Short Stemmed
F2 Generation
Mendel’s Law of Segregation
• Genes for different traits can segregate
(or separate) independently during the
formation of gametes
• This is because the two different alleles
that an organism has are on different
chromosomes in a homologous pair.
Mendel’s Law of Segregation
Parent Cell
Meiosis I
Meiosis II
Gametes
Practice
• What are the possible genetic contents of the
gametes made by a person with the genotype
BB?
• What are the possible genetic contents of the
gametes made by a person with the genotype
Tt?
Practice
• What are the possible genetic contents of the
gametes made by a person with the genotype
BB? B or B
• What are the possible genetic contents of the
gametes made by a person with the genotype
Tt?
Practice
• What are the possible genetic contents of the
gametes made by a person with the genotype
BB? B or B
• What are the possible genetic contents of the
gametes made by a person with the genotype
Tt? T or t
Making Sense of Mendel’s
Findings
• Probability-
Making Sense of Mendel’s
Findings
• Probability- the likelihood that a particular
event will occur
Making Sense of Mendel’s
Findings
• Probability- the likelihood that a particular
event will occur
–Scientists use probability to predict the
phenotypes and genotypes of the
offspring.
Making Sense of Mendel’s
Findings
• Probability- the likelihood that a particular
event will occur
–Scientists use probability to predict the
phenotypes and genotypes of the
offspring.
• Punnett Square-
Making Sense of Mendel’s
Findings
• Probability- the likelihood that a particular
event will occur
–Scientists use probability to predict the
phenotypes and genotypes of the
offspring.
• Punnett Square- a diagram that shows gene
combinations that might result from a
genetic cross
Making Sense of Mendel’s
Findings
• Probability- the likelihood that a particular
event will occur
–Scientists use probability to predict the
phenotypes and genotypes of the
offspring.
• Punnett Square- a diagram that shows gene
combinations that might result from a
genetic cross
–Punnett squares show predicted results,
not actual results.
Punnett Square
Parent 1
Gamete 1
Gamete 1
Offspring 1
Gamete 2
Offspring 2
Parent 2
Gamete 2
Offspring 3
Offspring 4
Let’s take a look at Mendel’s crosses that he completed to determine
his laws of heredity. We will use L to represent the allele for long stems
and l to represent the allele for short stem.
CROSSES INVOLVING ONE TRAIT
(MONOHYBRID CROSSES)
Homozygous x Homozygous
• When he crossed two pure-breeding plants for
the same version of the trait, all of the
offspring shared the same phenotype as the
parents.
Homozygous x Homozygous
LL
Parent 1
L
Gamete 1
L
Gamete 1
LL
Offspring 1
L
Gamete 2
LL
Offspring 2
LL
Parent 2
L
Gamete 2
LL
Offspring 3
LL
Offspring 4
Homozygous x Homozygous
Test Crosses
Test Crosses
• We can’t tell by looking at an individual with a
dominant phenotype if the individual’s genotype
is homozygous dominant (BB) or heterozygous
(Bb). What can we do to determine the genotype
of an individual with a dominant phenotype?
• Test cross:
Test Crosses
• We can’t tell by looking at an individual with a
dominant phenotype if the individual’s genotype
is homozygous dominant (BB) or heterozygous
(Bb). What can we do to determine the genotype
of an individual with a dominant phenotype?
• Test cross: crossing an organism with a dominant
phenotype, but unknown genotype, with a
homozygous recessive organism, then observing
the phenotypes of the offspring to determine the
unknown genotype