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Chapter 11Introduction to Genetics
• Gregor Mendel and his work (Section 11-1)
– Peas and Genetics– Genes and Dominance
• Probability and Punnett Squares (Section 11-2)
• Exploring Mendelian Genetics (Section 11-3)
– Independent Assortment– Mendel’s principles
• Beyond Mendelian Genetics
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XFirst Generation (F1)
100% pink!!!
Second Generation (F2)
X
3 pink, 1 blue - ¾ pink (75%), ¼ blue (25%)How did this How did this
happen?happen?
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Section 11-1
Genetics!!!
• Patterns of Inheritance• You inherit traits (physical characteristics)
from your parents- Heredity!• Heredity is what makes you unique
– Examples of Traits:• Blue, Green, Brown, Black, Hazel Eye color• Red, Brown, Black, Blonde hair color• Pale, Olive, Dark skin color• Tall, short, average heights• Or, pink and blue fur!
• GeneticsGenetics = the scientific study of heredityand its importance in biology
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Gregor Mendel• Gregor Mendel (1822), an Austrian
monk who studied inheritance patterns in pea plants, his work is now considered the foundation of modern genetics– He worked with ordinary garden peas, planted in
the garden at his monastery.– His love of plants and science allowed him to spend
a lifetime devoted to both.
• In 1866, he published a groundbreaking work that later became known as Mendel’s Laws on Heredity, but NO ONE BELIEVED HIM!!!
• Years later, his work was rediscovered, and modern genetics was born
Ah! What a lovely flower!
Yet another lovely flower! I
am truly in heaven!
Am I in heaven?
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What Mendel Did• Background:
– Fertilization = when the female’s egg and the male’s sperm (flower sperm = pollen) unite to produce an embryo
• Plants, animals, and most living things, sexually reproduce
• Sexual reproduction = combination of egg and sperm to create a new cell, or embryo
• Mendel’s peas were True-BreedingTrue-Breeding, meaning if they were allowed to self-pollinate, they would produce baby pea plants (offspring) identical to themselves– Mendel knew what to expect from his pea plants-
they should look exactly like their parent plant!
• He Cross-pollinated his pea plants, mixed up the parents, to see what the resulting plants would look like
Let’s cross you with the white flower.
Hmm, what have we here?
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What Mendel Found
• Mendel studied 7 different pea plant traits that varied from one individual plant to the next (like human traits!)
• These traits had 2 forms, such as either green seeds or yellow seeds, smooth pods or wrinkled pods– He crossed plants with each of the 7
contrasting characteristics and studied their offspring
• P = represents the parent generation
• F (from the Latin word fillius and filia- son and daughter)
• F1 = first generation
• F2 = second generation
• Hybrids = offspring of crosses between parents with different traits
Are you an F1 or F2?
P x P
F1 X F1
F2
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Mendel’s Experiment
P generation
tall short
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Mendel’s Experiment
tall short
F1 generation
tall tall
P generation
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Mendel’s Results
Seed Shape
Seed Color
Seed Coat Color
PodShape
PodColor
FlowerPosition
FlowerHeight
wrinkled green white
round yellow gray
constricted yellow terminal short
smooth greenaxial
tallRound dominant
Yellow dominant
Gray dominant
Smooth dominant
Green dominant
Ha! Those are MY peas!
Axial dominant
Tall dominant
All the F1 plants expressed only the dominant trait!
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Mendel’s Principles of Heredity
• Mendel learned 2 principles from these experiments:1. Biological inheritance is
determined by factors (we call them genes) that are passed from one generation to the next, Genes = chemical factors that
determine traits – each trait is controlled by 1 gene that occurs in 2 contrasting forms or alleles
Allele = a different form
of a gene
Hello!
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Box 14 Box 15
2. Principle of Dominance: some alleles are dominant and others are recessive
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Principle of Dominance
Eeek!
I’m so proud!
• An organism with a dominant allele for a particular form of a trait will always exhibit that form of the trait
• In other words, if you have the dominant allele, you will express that dominant trait
• An organism with a recessive allele for a particular form of a trait will exhibit that form only when the dominant allele is not present
• In other words, you must have 2 recessive alleles to express the recessive trait
I’m Dominant!!
Brown eyes = BB or Bb Blue eyes = bb
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Tall = TT or Tt
Short = tt
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Where did the recessive traits go?
• Mendel wanted to know why all his F1 plants expressed only dominant traits ?????
• He wondered, “Had all the recessive traits disappeared? Or were they still present in the F1 plants?”
• To answer this question, he allowed his F1 plants to self-
• pollinate
F1 X F1 F2
Naughty! Naughty!
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Mendel’s Experiment
P generation
tall short
F1 generation
tall tall
Tall, short, tall, tall
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Mendel’s Experiment
P generation
tall short
F1 generation
talltall
F2 generation
tall tall tall short
Tall, short, tall, tall, tall, tall, tall,
tall, SHORT! Ha!
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F1 Cross
• Mendel thought the results for his F1 cross were amazing!
• All the recessive traits re-appeared in the F2 offspring!
• This was due to segregation (separation) of alleles
• Segregation of the alleles happens when gametes (sex cells) are formed
• One trait comes from the father, one trait comes from the mother
I’m good!Man
of the Year
All in Box 18
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Segregation
TTtt
Tall
TTtt
Tall
F1 X
TT
TTTT
TT
TTtt TTtt tttt
Segregation
Gametes
F2
Hmmm….
Tall Tall Tall Short
tt Gametestt
3 Tall, 1 Short 3 :1 Ratio
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Genetics and Probability• Probability = the likelihood that a
particular event will occur• For example, tossing a coin
• Probability of heads = ½ or 50%• Probability of tails = ½ or 50%• If you flip a coin 3 times in a row, what is the
probability of heads each time?• Each coin toss is independent of the previous
toss, so ½ x ½ x ½ = 1/8 or 13% chance of all heads
• The way alleles segregate is completely random, like a coin toss (50% chance for each allele)
• We can use the principles of probability to PREDICT the outcome of genetic crosses
Section 11-2
Yeah, I look
good.
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Punnett Squares
• Punnett Squares
T t
T
tTall = TtTall = Tt
TT Tt
Tt tt
TT or tt = Homozygous
Tt = Heterozygous
TT, Tt, ttGenotype =
Phenotype = Tall, short
X
Why didn’t I think of
that?
Punnett Squares = tool used to predict and compare the genetic variations that may result from a cross
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Genotype = genetic makeup (Geno = genes)
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Phenotype = physical characteristics (Pheno = physical)
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Homozygous = 2 identical alleles for the same trait Box 25
Heterozygous = 2 different alleles for the same trait
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Fill in the Punnet Square
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BB
Punnett Squares
X
Phenotype = Brown eyes
Genotype = BB or Bb
Phenotype = Blue eyes
Genotype = bb
b
b
Bb
Bb
Bb
Bb
Genotype offspring = 100% Bb
Phenotype offspring = 100% brown eyes
B
b
b
b
Bb
Bb
bb
bb
Genotype offspring = 50% Bb, 50% bb
Phenotype offspring = 50% brown, 50% blue eyes
B b
b
B
Bb
BbBB
bb
Genotype offspring = 25% BB,50% Bb, 25% bb
Phenotype offspring = 75% brown, 25% blue eyes
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Mendelian Genetics• Mendel wondered if the traits
segregated independently, or were they somehow linked together
• His experiment = 2 factor Test Cross for F1 and F2
Section 11-3
Round Yellow peasGenotype: RRYY
Wrinkled Green peasGenotype: rryyX
100% RrYy, Round Yellow peasBox 26
I won!
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2 Factor Cross: F2
• Mendel’s F1 plants were RrYy, or all heterozygous for seed shape and color genes
• Mendel asked himself, “Would these alleles segregate independently? Or would they stay together?”
• To find out, Mendel crossed his F1 plants to create the F2 generation: RrYy x RrYy To segregate or not
to segregate, that ‘tis question.X
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2 Factor Cross: F2
Alleles for seed shape and color segregated
independently
Ah, my beautiful peas!
F2 plants :556 seeds315 round and yellow (parental)32 wrinkled and green (parental)209 combination of phenotypes (combo of alleles)
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1. Genes, passed from parents to offspring, determine the inheritance of biological characteristics.
2. When 2 or more forms (alleles) of a gene exist, some forms may be dominant and some recessive.
3. In sexual reproduction, each adult has 2 copies of each gene (one from each parent), and these genes segregate from each other when gametes are formed.
4. The alleles for different genes usually segregate independently of one another.
Therefore, thou must write all my Principles!
Mendel’s Principles
Thou must remember my
Principles!
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And, stop whining- start
writing!!!
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Principle of Independent Assortment
• Principle of Independent Assortment: genes for different traits can segregate independently during the formation of gametes– This helps to account for the many
genetic variations observed in plants, animals and other organisms
– Seed color isn’t tied to seed shape or plant height
– Just like having red hair doesn’t mean you have blue eyes, or being tall doesn’t mean you have a big nose
• Genes for different traits are independently assorted into the sex cells (eggs and sperm)
Did you know pollen is flower
sperm?
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Exceptions to Mendel’s Rules
• Some alleles are neither dominant or recessive – what????
• Some traits are controlled by multiple alleles or multiple genes
• Incomplete Dominance = cases when one allele is not completely dominant over another
What??? Say it ‘tisn’t so
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Section 11-4
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Incomplete Dominance
Pink Flowers!
Four o’clock plants
Red should be dominant over white, or vise versa, but neither is completely dominant, thus,
incomplete dominance. When you cross Red and
White Four O’clock Flowers, you get PINK
flowers!!!!
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Codominance
• Codominance = both alleles contribute equally to the phenotype
• The offspring is a mixture of both alleles
Red cow White cow X
A pink cow? I don’t think so.
Le Moo.
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Roan cowNeither white or redRed fur and white fur
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Multiple Alleles
• Multiple Alleles = when a gene has more than two alleles– Does NOT mean a person can have
more than two alleles for a single trait (still 1 gene from mom, 1 from dad)
– The trait itself has more than 2 forms (alleles)
– Ex. Blood types, A, B, AB, O• All are a type of human blood• But, humans can be either blood type
Blood type B = BB or BO
Blood type AB = AB
Blood type O = OO
Blood? I don’t do blood. Where are
my peas?
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Blood type A = AA or AOBox 35
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Polygenic Traits
• Polygenic traits = traits controlled by more than one gene
Poly = many, Genic = genes
I’m tall.
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If you see a graph like this on my test, or the TAKS test, then you know one gene can’t control the trait! Polygenic!
This range of heights and skin colors tells us more than 2 genes control both traits.
If 2 genes controlled height and 2 genes controlled skin color, we would see either tall or short people, light or dark skin, and nothing in between. Is that what we see?
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Drosophila melanogaster
• Thomas Hunt Morgan (1900s)- worked with Drosophila melanogaster (fruit fly) to study Mendel’s principles
• Why study fruit flies?– Produce lots of offspring (don’t we know
it)– Short life span (can do lots of tests)– Has variations we can cross
I prefer flowers. Especially
peas.
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So, Mendel’s principles apply to all organisms, not just plants!
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Genes and the Environment
• Genetics is only part of what determines the physical characteristics of an organism
• Our environment also plays a big role– Your behavior is partially determined by
genes inherited from your parents, but also by the environment in which you were/are raised
• Twin studies
– Plants are dependent on weather– Domesticated animals vs. wild animals
Wonder twin powers, Activate!
Form of.. A pea plant!
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Form of.. Pea soup?
So, don’t blame your genes
totally for your behavior - that’s mostly learned at home!
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Linkage and Gene Maps
• Genes are found on chromosomes, and we inherit whole chromosomes from our parents
• Therefore, it’s actually chromosomes that assort independently, not individual genes
• So, some genes are “linked” together by virtue of being on the same chromosome
Section 11-5
Gene for hair length
Gene for curly hair
I have curly hair, and I’m tall.
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Genetic Diversity
• Even if 2 genes are found on the same chromosome, they may not be linked forever
• Crossing Over during Prophase I of Meiosis leads to a genetic “mixing” up
• This generates Genetic Diversity
Crossing over
Stop that. It’s wrong! Or is it?
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Gene Maps
• The further apart two genes are on a chromosome, the more likely they are to be separated during meiosis
• The rate at which genes were separated and recombined is used to make Gene Maps
That doesn’t look like a pea plant.
Chromosome 19
Gene Map = shows the location of a variety of genes on a chromosome and how far apart the genes are
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End of Ch. 11
I hope thou hast enjoyed
learning about my work!
Go plant some peas!
Save the peas!
I wonder if anyone will miss me? Will they forget about
me and my research?
Hmm…pea soup sounds good, I
wonder if I have any peas left over?
