Section 11-1. Analyzing Inheritance. Interest Grabber. Offspring resemble their parents. Offspring inherit genes for characteristics from their parents. To learn about inheritance, scientists have experimented with breeding various plants and animals. - PowerPoint PPT Presentation
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Mendel and Heredity Analyzing Inheritance • Offspring resemble their parents. Offspring inherit genes for characteristics from their parents. To learn about inheritance, scientists have experimented with breeding various plants and animals. • In each experiment shown in the table on the next slide, two pea plants with different characteristics were bred. Then, the offspring produced were bred to produce a second generation of offspring. Consider the data and answer the questions that follow. Section 11-1 Interest Grabber Go to Section :
Transcript
Mendel and Heredity
Analyzing Inheritance
• Offspring resemble their parents. Offspring inherit genes for characteristics from their parents. To learn about inheritance, scientists have experimented with breeding various plants and animals.
• In each experiment shown in the table on the next slide, two pea plants with different characteristics were bred. Then, the offspring produced were bred to produce a second generation of offspring. Consider the data and answer the questions that follow.
Section 11-1
Interest Grabber
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Mendel and Heredity
• 1. In the first generation of each experiment, how do the characteristics of the offspring compare to the parents’ characteristics?
• 2. How do the characteristics of the second generation compare to the characteristics of the first generation?
Section 11-1
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ParentsLong stems short stems
Red flowers white flowers
Green pods yellow pods
Round seeds wrinkled seeds
Yellow seeds green seeds
First GenerationAll long
All red
All green
All round
All yellow
Second Generation787 long: 277 short
705 red: 224 white
428 green: 152 yellow
5474 round: 1850 wrinkled
6022 yellow: 2001 green
Mendel and Heredity
• 11–1 The Work of Gregor MendelA. Gregor Mendel’s Peas
B. Genes and Dominance
C. Segregation
1. The F1 Cross
2. Explaining the F1 Cross
Section 11-1
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Mendel and Heredity
KEY CONCEPT Mendel’s research showed that traits are inherited as discrete units.
Mendel and Heredity
Heredity: The transmission of traits from parents to offspring.
Who was Gregor Mendel?
Austrian monk and high school teacher born in 1822.
Father of Genetics (1800’s) study of heredity
Modern genetics is a core theme in biology.
Mendel and Heredity
Mendel laid the groundwork for genetics.
• Traits are distinguishing characteristics that are inherited.
• Genetics is the study of biological inheritance patterns and variation.
• Gregor Mendel showed that traits are inherited as discrete units.
• Many in Mendel’s day thought traits were blended.
Mendel and Heredity
Mendel’s data revealed patterns of inheritance.
• Mendel made three key decisions in his experiments.– use of purebred plants– control over breeding– observation of seven
“either-or” traits
Mendel and Heredity
• 4 stock plants:• Tall/Short Green/Yellow seeds• The peas were self pollinating and producing
an exact copy of the parent plant. (True Breeding)
• Mendel cross bred the seeds and got hybrid pea plants.
• How ? He took pollen from the male structures (anthers) of a tall plant and placed it on the female structures (pistil) of a short plant.
• All of the offspring were hybrid tall (F1).
Mendel and Heredity
Blended Inheritance – that sperm and egg traits mixed to form a intermediate offspring. If one parent tall and one short, offspring will be in between or medium height.
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To really appreciate Mendel, we have to keep in mind what people thought at the time.
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A. Mendel’s Peas
Chose garden peas to test.
Why?1.Grow quickly and easily in very little space.
2.True-breeding peas - all offspring show the same trait generation after generation (homozygous).
3.Variety of contrasting traits to study (tall v short, white v purple, etc.)
4.Easy to control breeding because closed flower doesn’t let random sperm/pollen in!
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1. Grow easily and quickly.• Could get at least 2
crops per year• Now we use flies or
bacteria
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2. True-breeding (Pure bred) predict offspring traits reliably from pure bred stock.
Tall x Tall always = tall offspring
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3. Variety of contrasting Traits• One stock of seeds would produce only tall plants,
another only short ones. • Mendel studied 7 individual traits
Seed Shape
Flower Position
Seed CoatColor
Seed Color
Pod Color
Plant Height
PodShape
Round
Wrinkled
Yellow
Green
Gray
White
Smooth
Constricted
Green
Yellow
Axial
Terminal
Tall
Short
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4. Easy to control breeding• male & female parts are in a closed flower –
other plant pollen can’t get in.
a) self-pollinate – fertilization in a single plant using own pollen (sperm) and egg to make a zygote (seed!)
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Mendel wanted to study the results of breeding 2 different plants, so he had to prevent self-pollination.
b) cross-pollination breeding two different
plants
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Checkpoint
1. What does it mean if an organism is true breeding?
2. What is the difference between self-pollination and cross-pollination?
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ANY QUESTIONS?
Mendel and Heredity
• Mendel used pollen to fertilize selected pea plants.
Mendel controlled thefertilization of his pea plantsby removing the male parts,or stamens.
He then fertilized the femalepart, or pistil, with pollen froma different pea plant.
– P generation crossed to produce F1 generation
– interrupted the self-pollination process by removing male flower parts
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B.Mendel’s experiments
Mendel studied 7 different traits.
What is a trait?
A specific inheritable characteristic.
P Generation are the parent plants.
F1 Generation are the 1st generation plants.
F2 Generation are the 2nd generation plants.
Cross bred plants and studied the results using math.
Can’t study them all at once
Mendel studied one trait at a time (1 variable) = good science!
13.1 Ecologists Study Relationships
Seed Shape
Flower Position
Seed CoatColor
Seed Color
Pod Color
Plant Height
PodShape
Round
Wrinkled
Round
Yellow
Green
Gray
White
Smooth
Constricted
Green
Yellow
Axial
Terminal
Tall
Short
Yellow Gray Smooth Green Axial Tall
Section 11-1Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants
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Mendel and Heredity
F1 –first filialF2 –second filial 20
a) P = true breeding parents (homozygous)– Tall x short
b) F1 = first filial (offspring of P, heterozygous)
– all tall
1. Bred true breeding plants.True tall to true short.
P - parent
Mendel and Heredity
F1 –first filial F2 –second filial
F2 = second filial (offspring of F1)
– 3 tall:1 short
2. Bred F1 x F1
P - parent
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What did Mendel expect?He expected medium plants! Blended inheritance was the dominant theory. Instead he got all tall in F1 and then roughly 3 tall for each short in F2. •How did short go away and then come back in a later generation?
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What did Mendel do?
• Repeat! Repeat! Repeat! = Good Science• He counted over a thousand plants for height alone! Still ~
3:1 ratio
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What do the results mean?
Had the short allele disappeared? Was it gone or was it still there in the F1 plants? How did he know?
– Still present, because it showed up in the F2
– AND it was unchanged. Short expression same as short purebred when seen again!
– Means Short and Tall are different versions of the same trait and do not get mixed together.
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Mendel and Heredity
• Mendel’s work led to 2 laws.• The law of segregation: Members of each pair
of alleles separate when the gametes are formed. (Homologous Chromosomes separate)
• The law of independent assortment: Pairs of alleles separate independently of one another during gamete formation.
Mendel and Heredity
What do the results mean?
1. Genes/traits are passed unchanged as a unit
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No blending!
Genes – DNA sequence on a chromosome that codes for specific protein(s) that determine traits (The chemical factors that determine traits.)
Alleles - different expressions of same gene for same trait Ex: one allele codes for tall, one allele codes for short but both the same gene coding for height
Mendel and HeredityWhat do the results mean?
2. Segregation of alleles – during gamete formation, alleles separate so you only inherit one copy of each gene from each parent
– F1 had to have both alleles to get a short plant in F2, so the allele for shortness had to be separated from the allele for tallness when passed to the F2.
– homologous chromosomes must separate• When does this happen during sexual reproduction???
MEIOSIS! Anaphase I
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Segregation of Alleles
Meiosis
Fertilization
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What do the results mean?
3. Principle of Dominance – one allele can mask another allele.
Tall allele dominated short allele.
Dominant – allele or trait that is seen when present, masks recessive allele. Capital letters: A
Recessive – allele or trait that is only seen if the dominant trait is NOT present. Lower case letters: a
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How do you tell which trait is dominant?
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Checkpoint
1. What is the difference between a gene and an allele?
2. How did Mendel know that the F1 generation still had the allele for short?
3. How is the segregation of alleles related to meiosis?
4. What is the Principle of Dominance?
31ANY QUESTIONS?
Mendel and Heredity
• Mendel observed patterns in the first and second generations of his crosses.
Mendel and Heredity
• Mendel drew three important conclusions.
– Traits are inherited as discrete units.– Organisms inherit two copies of each gene, one from
each parent.– The two copies segregate
during gamete formation.– The last two conclusions are
called the law of segregation.purple white
Mendel and Heredity
Tossing Coins
• If you toss a coin, what is the probability of getting heads? Tails? If you toss a coin 10 times, how many heads and how many tails would you expect to get? Working with a partner, have one person toss a coin
• ten times while the other person tallies the results on a sheet of paper. Then, switch tasks to produce a separate tally of the second set of 10 tosses.
Section 11-2Interest Grabber
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Mendel and Heredity
1. Assuming that you expect 5 heads and 5 tails in 10 tosses, how do the results of your tosses compare? How about the results of your partner’s tosses? How close was each set of results to what was expected?
2. Add your results to those of your partner to produce a total of 20 tosses.
Assuming that you expect 10 heads and 10 tails in 20 tosses, how close are these results to what was expected?
3. If you compiled the results for the whole class, what results would you expect?
4. How do the expected results differ from the observed results?
Section 11-2Interest Grabber continued
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• 11–2 Probability and Punnett SquaresA. Genetics and Probability
B. Punnett Squares
C. Probability and Segregation
D. Probabilities Predict Averages
Section 11-2
Section Outline
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Genes and Physical Traits• Genotype – genetic makeup of alleles
– Geno = “genes” – Ex: AA, Aa or aa; dominant or recessive,
heterozygous or homozygous• Phenotype – physical expression of traits or what
organism looks like!– Pheno = “to show”– Ex: tall or short, green or yellow, blue eyes or brown
eyes
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• All tall plants have the same phenotype, or physical characteristic of tallness.
• They do not, however, have
the same genotype, or genetic makeup (alleles!)
• Same phenotype but different genotype.
TALL TALL
Genotypes and Phenotypes are different.
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1. Can we know phenotype if we know the genotype?
2. Why?
3. Can we know the genotype if we know the phenotype?
4. Why not?
TALL TALL
Determining Genotypes and Phenotypes.
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Checkpoint
1. What are different forms of the same gene called?
2. For genotype TT, is this dominant or recessive? Homozygous or heterozygous?
3. What is the phenotype of a heterozygous plant if purple flowers dominate white flowers?
40ANY QUESTIONS?
Mendel and Heredity
KEY CONCEPT Genes encode proteins that produce a diverse range of traits.
Mendel and Heredity
What is homozygous?
Having two identical alleles for a trait.Homozygous Dominant – two dominant alleles = AA
Homozygous Recessive – two recessive alleles = aa
What is heterozygous?
Having two different alleles for a trait. = Aa
Mendel and Heredity
The same gene can have many versions.
• A gene is a piece of DNA that directs a cell to make a certain protein.
• Each gene has a locus, aspecific position on a pair ofhomologous chromosomes.
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• An allele is any alternative form of a gene occurring at a specific locus on a chromosome.
– Each parent donates one allele for every gene.
– Homozygous describes two alleles that are the same at a specific locus.
– Heterozygous describes two alleles that are different at a specific locus.
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Genes influence the development of traits.
• All of an organism’s genetic material is called the genome.
• A genotype refers to the makeup of a specific set of genes.• A phenotype is the physical expression of a trait.
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• Alleles can be represented using letters.
– A dominant allele is expressed as a phenotype when at least one allele is dominant.
– A recessive allele is expressed as a phenotype only when two copies are present.
– Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters.
Mendel and Heredity
• Both homozygous dominant and heterozygous genotypes yield a dominant phenotype.
• Most traits occur in a range and do not follow simple dominant-recessive patterns.
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KEY CONCEPT The inheritance of traits follows the rules of probability.
Mendel and Heredity
• What is probability?• The likelihood that an event will occur. Usually
expressed in a ratio.
• Probability can be used to predict the outcome of genetic crosses.
• What is a Punnett Square?• A diagram that shows the segregation of genes.
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Probability and Punnet Squares• Whenever Mendel crossed two hybrid plants (F1), he got
3:1 ratio or ¾ dominant and ¼ recessive.• Mendel realized that the
principles of probability
(MATH!!) could be used
to explain the results of
genetic crosses.
Mendel and Heredity
Genetics and Probability
• Ex: coin flip – probability of heads is 1 chance out of 2 possible outcomes = 1/2, or 50%.
• Does heads on the first flip change the probability of heads on the next? What if heads 10 times in a row – will next flip be more likely tails?
Past outcomes do not affect future ones
Probability - the likelihood that any particular event(s) will occur
Mendel and Heredity
Genetics and Probability
What is the probability that we will flip heads three times in a row?
Because each event is independent :
(probability of event)N = number of events
or
½ x ½x ½ = (½)3 = 1/8
1 in 8 chance that 3 heads flipped in a row
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Genetics and Probability
How is this related to genetics?Allele segregation is equally random and each event
independent.
Chances of inheriting a given allele from a heterozygous parent = 50% or 1/2
If parent, T or t – you have a 50% chance of either, same as heads or tails
Mendel and Heredity
Probability and Gender
Females = homozygous XXWhat is the probability that you will inherit an X from your
mother?
Males = heterozygous XY.What is the probability that you will inherit an X from your
dad? Probability of a Y?What is the probability of having a boy? Having a girl?Which parent’s genes determine your gender?What is the probability that a family with three children will
have all girls?(probability of event)N = number of events
½ x ½x ½ = (½)3 = 1/8
Mendel and Heredity
Checkpoint
1. What does probability mean?
2. Given that you have a 50% chance of having boy, what is the probability that your second child will be a boy if your first is girl?
3. What is the probability that a family of four will be all girls?
55ANY QUESTIONS?
Mendel and Heredity
• Why Punnett squares?• Predicts the probability of a cross between two
organisms.• Rules:• Dominant allele represented by a Capital letter (T for
tall)• Recessive allele represented by a lower case letter (t
for short)• The letters designate the two forms of one gene, the
two alleles for a monohybrid cross.• Every cell in your body has at least two alleles for
every trait, one from Mom and one from Dad)
Mendel and Heredity
Punnett squares illustrate genetic crosses.
• The Punnett square is a grid system for predicting all possible genotypes resulting from a cross.– The axes represent
the possible gametesof each parent.
– The boxes show thepossible genotypesof the offspring.
• The Punnett square yields the ratio of possible genotypes and phenotypes.
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Punnet Squares
Punnett square – grid showing possible gene combinations for offspring from a given genetic cross.
• predicts genetic variations and their probability
• Shows phenotype & genotype ratios
Mendel and Heredity
Parents
Offspring
gametes
PUNNETT SQUARE
Mendel and Heredity
Setting up a Punnett Square
1. Determine Parent genotype.
2. Capital for dominant, lower case recessive.
3. Top and left letters = divide parent alleles
4. Bring down from top and over from left to create possible genotype combinations for offspring.
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Tt
tt
Tt
tt
Short plant x
Tall heterozygote
Mendel and Heredity
Checkpoint
We crossed a heterozygous black female with a white male.
What is the genotype of the female? The male?
Draw punnett square for this cross.
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Black (B) hair dominates white (b) in guinea pigs.
Bb
B b
b
b
Bb
bb
bb
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Ratios and Punnett Squares
Genotype ratio – number of each type of offspring genotype predicted by punnett square
• For a single trait (monohybrid cross) –homozygous dominant: heterozygous: homozygous recessive
#TT : #Tt : #tt
Phenotype Ratio – number of each type of offspring phenotype predicted by a punnett square
dominant:recessive traits#Tall : #short
Mendel and Heredity
• Monohybrid Cross: • Provided data for one pair of contrasting traits.
• What are the possible genotypes that can result?
• What are the possible phenotypes that can result?
• What is the ratio of tall to short plants in a hybrid cross?
• Does this ratio agree with Mendel’s result in the F2 generation?
Mendel and Heredity
A monohybrid cross involves one trait.
• Monohybrid crosses examine the inheritance of only one specific trait.– homozygous dominant-homozygous recessive: all
• A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype.
Mendel and Heredity
Checkpoint
How many piglets are homozygous dominant?
Heterozygous?
Homozygous recessive?
What is the genotype ratio?
How many black? White?
What is the phenotype ratio?
67ANY QUESTIONS?
Black (B) hair dominates white (b) in guinea pigs.
BbB b
bb
Bbbbbb
Mendel and Heredity
A dihybrid cross involves two traits.
• Mendel’s dihybrid crosses with heterozygous plants yielded a 9:3:3:1 phenotypic ratio.
• Mendel’s dihybrid crosses led to his second law,the law of independent assortment.
• The law of independent assortment states that allele pairs separate independently of each other during meiosis.
Mendel and Heredity
Law of Independent Assortment
• genes for different traits can segregate independently during the formation of gametes.
• Independent assortment = genetic variation
• Mendel concluded that the inheritance of one trait does not influence the inheritance of a second trait
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Independent Assortment occurs in Meiosis – Metaphase I
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R = roundr = wrinkled
Y = yellowy = green
R
R
R RR R
R
R
yY
r r
r
rr
r
r
Y
YYYY
Y
y
yy
y
yy
Mendel and Heredity
Heredity patterns can be calculated with probability.
• Probability is the likelihood that something will happen.• Probability predicts an average number of occurrences, not
an exact number of occurrences.
• Probability =number of ways a specific event can occur
number of total possible outcomes
• Probability applies to random events such as meiosis and fertilization.
Mendel and Heredity
Probability and Punnett Square
– Probabilities predict averages, not exact outcomes
– Probability is more accurate when you have more chances
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Exploring Mendelian Genetics• Because organisms are made up of more than one trait,
Mendel wondered if they sort independently.• For example, does the gene that determines whether a
seed is round or wrinkled in shape have anything to do with the gene for seed color?
• Must a round seed also be yellow?
Mendel and HeredityDIHYBRID CROSS
Crossing organisms with genes for two different traits = 2X as many possible gametes.
If we cross RRYY with rryy – what are the possible gametes?
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Mendel and Heredity
DIHYBRID CROSS : punnett square for true breeding or homozygous parents.
R = roundr = wrinkledY = yellowy = green
Mendel and HeredityDIHYBRID CROSS
What possible gametes do we get from crossing RrYy and RrYy?
Mendel and HeredityDIHYBRID CROSS
What possible gametes do we get from crossing RrYy and RrYy?
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ry
rY
Ry
RY
ryrYRyRY
RRYY RRYy RrYY RrYy
RRYy RRyy RrYy Rryy
RrYY RrYy rrYY rrYy
RrYy Rryy rrYy rryy
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heterozygous
Offspring have combinations of alleles not found in earlier generations = alleles segregated
independently
Mendel and HeredityDIHYBRID CROSS
Classic phenotype ratio from dihybrid cross of heterzygotes = 9:3:3:1
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Summary of Mendel’s Principles1. Traits come from your inherited genes.
2. Genes may have more than one allele and some are dominant.
3. Your two copies of each gene (one from each parent) are segregated or separated when gametes form.
4. Alleles for different genes usually segregate independently of one another.
Mendel and Heredity
Checkpoint
We crossed a female heterozygous for both long black hair with a short, white haired male.
What is the genotype of the female? The male?
What are the possible gametes for the female?
What are the possible gametes for the male?
Draw the dihybrid punnett square for this cross.
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Black (B) hair dominates white (b) Long (L) dominates short(l)
81ANY QUESTIONS?
Mendel and Heredity
• BbLl• BL• Bl• bL• bl
Mendel and Heredity
bl bl bl bl
BL
Bl
bL
bl
Mendel and Heredity
bl bl bl bl
BL BbLl BbLl BbLl BbLl
Bl Bbll Bbll Bbll Bbll
bL bbLl bbLl bbLl bbLl
bl bbll bbll bbll bbll
4 white long
4 white short
4 black short
4 black long
4 bbll 4 bbLl 4 Bbll 4 BbLl
Mendel and Heredity
Height in Humans
Height in pea plants is controlled by one of two alleles; the allele for a tall plant is the dominant allele, while the allele for a short plant is the ecessive one. What about people? Are the factors that determine height more complicated in humans?
Section 11-3Interest Grabber
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Mendel and Heredity
• 1. Make a list of 10 adults whom you know. Next to the name of each adult, write his or her approximate height in feet and inches.
• 2. What can you observe about the heights of the ten people?
• 3. Do you think height in humans is controlled by 2 alleles, as it is in pea
C. Beyond Dominant and Recessive Alleles1. Incomplete Dominance
2. Codominance
3. Multiple Alleles
4. Polygenic Traits
D. Applying Mendel’s Principles
Section 11-3Section Outline
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Mendel and Heredity
Mendel’s Principles
1. Inheritance of traits is determined by genes that are passed from parents to offspring.
2. When two or more forms of a gene exist they may be dominant or recessive
3. In sexually reproducing organisms, genes are segregated during gamete formation and a new individual receives a set from each parent.
4. Alleles for different genes usually segregate independently.
Mendel and Heredity
KEY CONCEPT Phenotype is affected by many different factors.
Mendel and Heredity
Genetics can be affected by 5 other different heredity patterns.
1.Incomplete Dominance
2.Codominance
3.Polygenic Traits (Multiple Genes)
4.Environmental Influences
5.Sex linked traits
Mendel and Heredity
Other Dominance Possibilities:
What is incomplete dominance?
Occurs when one allele is not completely dominant over another. Example: Mixing of colors in flowers.
What is Codominance?
Similar to incomplete, occurs when both alleles contribute to the phenotype. Example: Blending of fur color.
Mendel and Heredity
Phenotype can depend on interactions of alleles.
• In incomplete dominance, neither allele is completely dominant nor completely recessive.– Heterozygous phenotype is intermediate between
the two homozygous phenotypes
– Homozygous parental phenotypes not seen in F1 offspring
13.1 Ecologists Study Relationships
Section 11-3Figure 11-11 Incomplete Dominance in Four O’Clock Flowers
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13.1 Ecologists Study Relationships
Section 11-3Figure 11-11 Incomplete Dominance in Four O’Clock Flowers
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1. Incomplete Dominance
• cross between red-flowered (RR) and white-flowered (WW) plants consists of pink-colored flowers (RW).
• What happens if you breed the pink flowers?
neither allele is completely dominant so creates a BLEND
Mendel and Heredity
• Codominant alleles will both be completely expressed.
– Codominant alleles are neither dominant nor recessive.
– The ABO blood types result from codominant alleles.
• Many genes have more than two alleles.
Mendel and Heredity
2. Codominance
• both alleles expressed in the phenotype – NOT blended.
Mendel and Heredity
CB CB
CW
CW CBCW
CBCW
CBCW
CBCW
CODOMINANCE In Chickens
Speckled NOT grey!
Mendel and Heredity
Mendel and Heredity
Checkpoint
What is the difference between incomplete dominance and codominance?
If a A is codominant with B and O is recessive to both, what blood types could the offspring be for a heterozygous blood type A crossed with a heterozygous blood type B?
What is the antigen attached to RBCs for type A blood? Type B blood? Type O Blood?
100 100ANY QUESTIONS?
Mendel and Heredity
What are multiple alleles?
Genes that have more than two alleles for a trait. Example: Blood type in humans
What are polygenic traits?
Traits that are controlled by two or more genes. Example: Skin color in humans.
Mendel and Heredity
Many genes may interact to produce one trait.
• Polygenic traits are produced by two or more genes.
Order of dominance: brown > green > blue.
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3. Multiple Alleles• Genes with more than two alleles
• This does not mean that an individual can have more than two alleles. It only means that more than two possible alleles exist in a population.
• One of the best-known examples is blood type in humans.
Mendel and Heredity
Human Blood Types
• 3 blood type alleles gene: – A = makes A surface
protein/or antigen– B = makes B surface protein/or
antigen– O doesn’t make either.
• A and B alleles are codominant to each other & both are dominant over recessive O allele.
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Mendel and Heredity• Antigens: Proteins produced on the blood cells.• Antibodies are produced in the blood plasma against
these A and B antigens, and continue to be produced throughout a person’s life.
• A person normally produces antibodies against the antigens that are not present on his or her red blood cells. For example, a person with antigen A on his red blood cells will produce anti-B antibodies; a person with antigen B will produce anti-A antibodies; a person with neither A or B antigens will produce both anti-A and anti-B antibodies; and, a person with both antigens A and B will not produce these antibodies.
• If blood cells are mixed with antibodies the cells will clump together. This is called agglutination. This is why it can be very dangerous if you receive the wrong blood type in a transfusion.
Mendel and Heredity
Blood typing
Blood typing is performed by mixing a small sample of blood with anti-A or anti-B antibodies (called antiserum), and the presence or absence of clumping is determined for each type of antiserum used. If clumping occurs with only anti-A serum, then the blood type is A. If clumping occurs only with anti-B serum, then the blood type is B. Clumping with both antiserums indicates that the blood type is AB. No clumping with either serum indicates that you have blood type O.
Mendel and Heredity
Human Blood Types
What antibodies would be made by a person with type A blood?
Type B blood?
Type AB blood?
Type O blood?
What is antisera?
Which type is the universal donor?
Which type is the universal receiver?
Is your blood type a genotype or phenotype?
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4. Polygenic Traits
• Traits controlled by interaction of two or more genes
• Polygenic =“many genes.” • Ex: Hair color, eye color, skin color all the result of
several genes
Mendel and Heredity
• Labrador retrievers can be black, brown, or yellow. • Two genes control this. One for producing color (Black
over brown) and one for depositing the color in the fur (homozygous recessive = yellow).
Mendel and Heredity
• Skin and eye color are polygenic traits in humans.
• At least 7 for eye color.
Mendel and Heredity
Mendel and Heredity
Environmental Influences:
Phenotype can depend on conditions in the environment.
Conditions can cause a gene to shut down or turn on in coat color.
This allows the animal to blend in with its background.
Mendel and Heredity
The environment interacts with genotype.
• Height is an example of a phenotype strongly affected by the environment.
• The sex of sea turtles depends on both genes and the environment
• Phenotype is a combination of genotype and environment.
Mendel and Heredity
• An epistatic gene can interfere with other genes.
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ENVIRONMENT INFLUENCES GENETIC TRAITS
Environment factors like diet, exercise, exposure to
toxic agents, or medications can all influence our genes
and traits.
I got the “fat” gene.
13.1 Ecologists Study Relationships
concluded that
which is called the
which is called the
GregorMendel
Law ofDominance
Law ofSegregation
Peaplants
“Factors”determine
traits
Some alleles are dominant,
and some alleles are recessive
Alleles are separated during gamete formation
Section 11-3Concept Map
Go to Section:
experimented with
Mendel and Heredity
Linked Genes
• Mendel concluded that traits are assorted independently, but some traits are Linked
• Linked genes: Genes usually inherited together because on same chromosome
Mendel and HeredityLinked Genes
Ex: Blue eyes, white fur tigers
Mendel and Heredity
Genes on the sex chromosomes are linked.
i. Y- Linked genes Y has few genes – mostly gender determining (boy or girl). – Y only in males so these genes only affect males.
ii. X-linked genes Many genes on X chromosome– Affects mostly males because only one copy of X– Male copy of X from MOM (Dad gave Y to son)– Females less affected because two copies of X = have to
inherit trait from both parents.– Heterozygous females are carriers for sex linked traits.– EX: baldness, colorblindness
Sex-Linked Genes
Mendel and Heredity
Baldness is X-linked recessive.
Grandpa bald = XbY X Grandma = XBXB
Daughter = XBXb marries normal Male
her sons – 50% XB(normal)
50% Xb(bald)
Sex-Linked Baldness
This is why men should look their mom’s dad for probability of baldness. But beware grandma could be a carrier too!
Mendel and Heredity
Crossing Over affects linked genes.
• Crossing over – exchanging DNA during prophase
• Genes closer on the chromosome LESS likely to be separated by crossing over.
Mendel and Heredity
Chromosome MappingThe farther apart genes are, the higher probability
that they will be separated by crossing over.– Scientists conduct experiments to determine how
frequently genes of a particular trait are separated from one another.
• Chromosome map - diagram of the linear sequence of genes on a chromosome.
• Two genes that are separated by crossing-over 1 percent of the time are considered to be one map unit apart.
Mendel and Heredity
Summary of Mendel’s Principles1. Traits come from your inherited genes.
2. Genes may have more than one allele and some are dominant.
3. Your two copies of each gene (one from each parent) are segregated or separated when gametes form.
4. Alleles for different genes usually segregate independently of one another.
Mendel and Heredity
Beyond Mendel – Other Patterns of Inheritance
1. Most genes have more than two alleles.
2. Some alleles are neither dominant nor recessive (codominance & incomplete dominance)
3. many traits are controlled by multiple genes.
4. Some genes are linked and do not segregate independently - on the same chromosome so inherited together.
Mendel and Heredity
Checkpoint
What is a linked gene?
Why do X-linked traits affect males more than females?
How does crossing over affect linked genes?
If the sequence of genes on a chromosome are X, Y, Z , D; which two genes are most likely to be unlinked by crossing over?
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