Bell Ringer 1.Fill in the table correctly. MitosisMeiosis Creates somatic cells Concerns sexual...
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Transcript of Bell Ringer 1.Fill in the table correctly. MitosisMeiosis Creates somatic cells Concerns sexual...
Bell Ringer1. Fill in the table correctly.
Mitosis Meiosis
Creates somatic cells
Concerns sexual reproduction
Forms haploid daughter cells
Used for growth and repair
Forms unique cells
Mendelian Genetics
• We can determine an organism’s physical traits (characteristics) by examining its chromosomes.• Chromosomes are made up of a series of genes,
sequences that code for proteins. • In the mid-1800s, Gregor Mendel experimented with pea
plants. He discovered that he could predict what the offspring of pea plants would look like, as the parents were passing down their physical traits to their offspring.• This lead to two vital laws: the laws of segregation and
independent assortment.
Segregation
• The law of segregation states that every physical trait has a unique gene that codes for it. All of the different possibilities for each trait are called alleles.• Example: alleles for eye color: black, brown, blue, etc.
• Since you have two of every chromosome, you have two alleles for ALL of your traits. Your alleles are split up when forming new gametes!
Independent Assortment• The DNA in your cells is
randomly separated in anaphase I. • For each chromosome
pair, there is a 50% chance of getting either chromosome.• Independent
assortment: the idea that each gamete randomly receives chromosomes in meiosis.
Alleles• One pair of alleles will
determine one specific physical trait. In traditional Mendelian genetics, all traits have two possible alleles:• A dominant allele, which
will ALWAYS dictate the physical trait if present
• A recessive allele, which ONLY dictates the physical trait if there are NO dominant alleles present
Alleles• The exact pair of alleles
is referred to as a genotype. Your physical trait is called a phenotype.• Genotype – “genes” –
genetic sequences• Phenotype –
“physical” – physical appearance
• Genotype ALWAYS controls phenotype!
Alleles
Rules:• Dominant alleles are typically given a capital letter.
Recessive alleles receive a lowercase letter.• Example: if yellow peas are dominant, and green peas
recessive, then Y = yellow, and y = green.• If the genotype contains ANY dominant alleles, the
phenotype will be dominant.• So, BOTH YY and Yy will produce YELLOW peas.
• You will ONLY see the recessive trait if you have TWO recessive alleles.• In other words, the ONLY way to make green peas is with
the genotype yy!
Alleles
Rules:• If you have two of the same alleles, you have a
homozygous pair. “Homo-” means the same.• If you have two different alleles, you have a
heterozygous pair. “Hetero-” means different.• Using our previous example of yellow and green peas:• The genotype YY is homozygous dominant, and makes
yellow peas.• The genotype Yy is heterozygous, and makes yellow peas.• The genotype yy is homozygous recessive, and makes
green peas.
Punnett Square• We can use a device
called a Punnett square to predict what offspring will look like.• A Punnett square is
a grid that shows all possible offspring.
Punnett Square• Monohybrid squares
are very easy to use:1. Take the genotype
of one parent, and split the alleles. Place them on the top of the square.• Example: YY crossed
with yy.
Punnett Square• Monohybrid squares
are very easy to use:2. Take the genotype
of the other parent, and split the alleles. Place them to the left of the square.• Example: YY crossed
with yy.
Y Y
Punnett Square• Monohybrid squares
are very easy to use:3. Fill in your square
by crossing the alleles together.• Example: YY crossed
with yy.
Y Y
y
y
Punnett Square• What genotypes will
our offspring be?
• What phenotypes will our offspring be?
Y Y
y Yy Yy
y Yy Yy
Common Monohybrid Crosses• We will examine
some of the most common monohybrid crosses you will see.• Pay close attention to
the genotypic and phenotypic outcomes!• For our examples, P =
purple flowers, p = white flowers.
Common Monohybrid Crosses• Crossing a pure
dominant with a pure recessive.• Example: PP x pp• Genotypic ratio:
100% Pp (hybrid)• Phenotypic ratio:
100% purple flowers
P P
p Pp Pp
p Pp Pp
Common Monohybrid Crosses• Crossing two
hybrids.• Example: Pp x Pp• Genotypic ratio: 1 PP:
2 Pp: 1 pp • 25%/50%/25%
• Phenotypic ratio: 75% purple flowers: 25% white flowers• 3:1 purple to white
P p
P PP Pp
p Pp pp
Common Monohybrid Crosses• Crossing a hybrid
with a pure recessive.• Example: Pp x pp• Genotypic ratio: 50%
Pp: 50% pp• 1 Pp: 1 pp
• Phenotypic ratio: 50% purple flowers: 50% white flowers• 1:1 purple to white
P p
p Pp pp
p Pp pp
Dihybrid Crosses• Say you want to cross
a tall purple flower with a short white flower. You will be crossing two different traits.• Can we find out what
the offspring will look like?
Dihybrid Crosses• According to Mendel’s
law of independent assortment, the genes for two different traits will always be on different chromosomes.• We CAN determine how
two different traits can be passed down, though. This requires the use of a dihybrid cross.
Dihybrid Cross• In a dihybrid cross, you
will cross two traits at the same time.• Since each gamete has to
have one copy of each chromosome, you need to assign each side of the Punnett square TWO letters; one for each trait!
• http://www.youtube.com/watch?v=PdQPXVZqyT8
Dihybrid Crosses• All organisms in a
dihybrid cross will have four alleles.• You’ll need to
separate them into gametes using the FOIL method!
• Example: Parent has the genotype AaBb.• Front: AB• Outside: Ab• Inside: aB• Last: ab
Dihybrid Crosses• Do the same for the
other parent.• Example: Parent has
the genotype AaBb.• Front: AB• Outside: Ab• Inside: aB• Last: ab
AB Ab aB ab
Dihybrid Crosses• Now, fill in each cell
of the dihybrid Punnett square.• Always keep the
same letters together.• Also, keep the letters
in the same order!
AB Ab aB ab
AB
Ab
aB
ab
Dihybrid Crosses
AB Ab aB ab
AB AABB AABb AaBB AaBb
Ab AABb AAbb AaBb Aabb
aB AaBB AaBb aaBB aaBb
ab AaBb Aabb aaBb aabb
Dihybrid Crosses
• From there, you can determine the genotypic and phenotypic ratios.• Remember, genotypic ratios are the number of
different sequences, and phenotypic ratios are the number of different appearances.• When counting genotypes, ALWAYS work from
most to least dominant.
Dihybrid CrossesSequence Number
AABB 1
AABb 2
AAbb 1
AaBB 2
AaBb 4
Aabb 2
aaBB 1
aaBb 2
aabb 1
AB Ab aB ab
AB AABB AABb AaBB AaBb
Ab AABb AAbb AaBb Aabb
aB AaBB AaBb aaBB aaBb
ab AaBb Aabb aaBb aabb