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Genetics. Chapter 7. What we thought before Mendel?. Aristotle (sometime in the 400’s) Thought we were composed of “vapors” & “fluids” “Fluids”- male ejaculate “purified blood” b/c it wasn’t red This first led to the thought that heredity was related to blood

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Chapter 7

What we thought before mendel
What we thought before Mendel?

Aristotle (sometime in the 400’s)

  • Thought we were composed of “vapors” & “fluids”

    • “Fluids”- male ejaculate “purified blood” b/c it wasn’t red

    • This first led to the thought that heredity was related to blood

    • “Vapors”- female “invisible particles”

  • During intercourse these, fluids and vapors combine, thus creating offspring similar to parents.

We can see everything with microscopes
We can see everything with Microscopes

  • Theory of Preformation (1600-1700)- Thought they could see “little people” in sperm when viewed under a microscope.


  • Schools in 1800’s taught acquired characteristics- that you can alter yourself to affect your offspring.

    • Ex: playing music, building muscles, smarts

  • We now call this Epigenetics or changes in gene expression by mechanisms other than changes in DNA.

Epigenetics continued
Epigenetics Continued…

  • It was first rejected but now recent evidence has shown might have been right all along.

  • This idea was discovered in mice by the work of Randy Jirtle

  • He discovered that what a mother mouse ate during pregnancy can have a effect on gene expression in the next generation of mice.

    • This food was high in methyl groups, a substance that can turn on and off gene expression.

Those poor rats
Those poor Rats

  • August Weismann(1883)- experiment on rats by cutting off their tails

    • Rats with cut tails produced rats with tails (~20x)

    • Cast doubt on Aristotle’s theory

    • Also proposed the idea of Somatic and Germ tissue.

Gregor mendel 1822 1884
Gregor Mendel (1822-1884)

  • THE Father of Genetics

  • Worked on Pea Plants (Pisumsativum)

  • In 1866, his papers were 1st published but weren’t found until the 1900’s.

Why pea plants
Why Pea Plants?

  • They reproduced quick and with a large amount of offspring

  • They contained a wide variety of variation (to which he studied and composed 7 traits)

  • Both male and female parts were on one flower

  • Very convenient to work with.

3 steps that led to his discovery
3 Steps that led to his Discovery

  • Had plants self-pollinate until he was sure that it was a true-bred trait.

    • Called this the Parental(P) Generation

  • He then mated the two opposite traits via cross-pollination.

    • Called this the Filial (F1) Generation

  • He let those offspring then self-pollinate.

    • F2 Generation. Counted the number of each trait that was produced.

Terms and how they relate to genetics
Terms and How they relate to genetics

  • Gene- a segment of DNA that transmits information from parent to offspring.

  • Allele- Alternative forms of a gene for a trait.

    • Ex: T, t

  • Dominant- An allele that has a higher potency.

More terms
More Terms

  • Recessive- a copy of an allele that is not readily expressed unless it contains another recessive allele.

  • Homozygote- 2 alleles are similar. Purebred.

    • Ex: RR, rr

  • Heterozygote- alleles are different. Hybrid/mutt.

    • Ex: Rr

  • Phenotype- Physical expression of a gene.

    • Ex: Tall, short

  • Genotype- Actual genetic construction.

    • Ex: AA, aa, Aa

Mendel s genetic laws
Mendel’s Genetic Laws

  • Law of Dominance

  • Law of Segregation

  • Law of Independent Assortment

Law of dominance
Law of Dominance

  • Only the dominant allele in a heterozygote is expressed.

  • Dominant is always put first and capitalized when written out.

  • Ex: SS= Smooth

    Ss= Smooth

    ss= Wrinkled

Law of segregation
Law of Segregation

  • 2 alleles of a parent separate during Sexual Reproduction and only one is randomly chosen to be passed to offspring.

  • Mendel created this law by saying that his “factors” split during meiosis.

  • Walter Sutton- found that chromosomes also split during meiosis and that Mendel’s “factors” were on these chromosomes. We call this the chromosomal theory of inheritance.





How segregation relates back to meiosis
How Segregation relates back to Meiosis




Parental Gametes:

Generation 1:

RR rr

Only R only r


Law of independent assortment
Law of Independent Assortment

  • The segregation of 1 pair of alleles occurs independently of the segregation of any other pair.

  • We inherit one and then the other.

Using probability and ratios
Using Probability and Ratios

  • Mendel was a mathematician so he used math to predict genetic outcomes.

  • Probability uses rules that can predict how genes will be distributed among the offspring of two parents.

    Probability = # of one outcome

    # of total outcomes

  • Ex: Rolling dice or Flipping a coin.

Monohybrid cross and punnett squares
Monohybrid Cross and Punnett Squares

  • Only using one trait and determining the outcome.

Dihybrid cross and law of ia
Dihybrid Cross and Law of IA

  • Using two pairs of contrasting traits.

How many different gametes
How many Different Gametes?

  • When given Allele combinations, we can use math to figure out how many possible gametes could be produced.

  • We know that there are only 2 possibilities that the gamete can have for one trait.

    • Its either going to have a Dominant or a Recessive Allele

  • Ex: AA Aaaa




How many different gametes can you have out of the following combinations
How many DIFFERENT Gametes Can you have Out of the following Combinations?

  • AABb

    1 x 2 = 2 possible different gametes (AB or Ab)

  • CcDdEe

    2 x 2 x 2 = 8 possible different gametes

    (CDE, CDe, CdE, Cde, cDE, cDe, cdE, cde)

  • ffGgHhIiJJ

    1x2x2x2x1 = 8 possible different gametes

    (fGHIJ, fGHiJ, fGhiJ, fGhIJ, fgHIJ, fgHiJ, fghIJ, fghiJ)

One last problem
One last problem.


    2x 2 x1 x1x1x1x1 x1x1x1x2x2 x2 x1 x1x1 = ?

    =32 possible different gametes

  • Now Imagine how our genes work and in each gamete we have 23,000 different genes.

  • That would be 2^23,000 = error

  • That is a whole lot of different gametes.

How many phenotypes genotypes
How many Phenotypes/Genotypes?

  • The secret to this is the mastery of the F.O.I.L.

  • First, Outside, Inside, Last

    For example: lets look at a monohybrid cross

    Aa x Aa

    (A a)x(A a)

    Four pairs of alleles: AA, Aa, Aa, aa

How many phenotypes genotypes1
How Many Phenotypes/Genotypes

How many Phenotypes are possible in the following Combination?

Aabb x AaBb

Aa x Aa bb x Bb

AA, Aa, Aa, aa Bb, bb, Bb, bb

2 x 2= 4 phenotypes


Aa x Aa bb x Bb

AA, Aa, Aa, aa Bb, bb, Bb, bb

3 x 2 = 6

Ratio problems and quiz
Ratio Problems and Quiz

  • The handout for today contains the ratio problems. They will be due on

  • Also, a quiz over the previous material and the 4 exceptions to Mendel on:


Exceptions to mendel
Exceptions to Mendel

  • Multiple Alleles

  • Incomplete Dominance

  • Co-dominance

  • Lethality

Multiple alleles
Multiple Alleles

  • More than 2 alleles exist for some gene

    • Means more phenotypes and genotypes to deal with.

  • Ex: Coat color in rabbits

    • C+- agouti

    • Cch- chinchilla

    • Ch- Himalayan

    • C- albino

    • C+ > Cch > Ch > C

Incomplete dominance
Incomplete Dominance

  • Heterozygote has a phenotype intermediate to the two homozygote types.

  • Ex: Snapdragon color

    • RR= Red

    • Rr= Pink

    • rr= White

    • Phenotype ratio is similar to genotype

    • 1:2:1

Co dominance

  • Both alleles of a Heterozygote are expressed

  • Ex: Blood Types

    • IA – A Antigen IB- B Antigen i= no Antigen

    • Antigen- Proteins that mark you as being you.

      Phenotypes Genotypes

      A IAIA, IAi

      B IBIB, IBi

      AB IAIB

      O ii


  • Some offspring have a reduce chance to live because of their gamete.

  • Ex: Corn

    • G- Green color- produces chlorophyll

    • g- Yellow Color- no chlorophyll

    • GG and Gg- Green= live

    • gg= Yellow = die b/c no chlorophyll

    • Genotype ratio- 1:2

Our plan of attack
Our Plan of Attack


  • Course Website: Write this down

  • Quick Explanation of the Lab.

  • Do the Lab.

  • The lab will not be due until TUESDAY.

  • There is a quiz TOMORROW over the notes so far.

  • The single page handout is due TOMORROW

Role of the x and y chromosomes
Role of the X and Y Chromosomes

  • Females – XX

  • Males – XY

  • Sperm determines sex

    • Only true of Fruit flies and Humans

    • Region on Y chromosome that determines sex= SRY

  • Heterogametic Sex- Gender has two different sex chromosomes

  • Homogametic Sex- Gender has the same sex chromosomes

Other sex are determined differently
Other Sex are determined differently

  • Fish, bird, reptiles

    • Homogametic- Males Heterogametic- Females

      • ZZ ZW

  • Bees and other select insects

    • They don’t have sex chromosomes but rather male or female determined by polyploidy.

    • Males- n Females- 2n

  • Marine worm

    • Females release pheromones that determines what they develop into.

    • No adult females- females adult females- males

Sex linked genes
Sex- Linked Genes

  • First studied by Thomas Morgan Hunt

  • Used Red and white eyed Fruit flies

    P: red females and white males

    F1: Red females and males

    F2: Red females and males and White males

    Sex-linked because the gene is located on X chromosome

Sex linked
Sex- Linked

Female Male

WW- Red WY- Red

Ww- Red wY- White

ww – White

  • Hemizygous- only one allele of a gene is present.





  • Complete the ENTIRE packet

  • I will collect it the day of the test which is


  • That means the 10 page packet is dueFEBURARY 18th

  • If you have any questions over the problems I am always here typically a half hour before and after school for help.

Why do we use fruit flies for genetics and not humans
Why do we use Fruit flies for Genetics and not Humans?

  • Humans long generation time.

    • About 2 weeks from generation to next for fruit flies.

  • Humans produce small # of offspring/ generation

    • Fruit flies produce ~ 100-200

  • Humans large # of chromosomes

    • Fruit flies have 8

  • Ethical problems with humans

    • No one cares that much about flies.

Genetic disorders
Genetic Disorders

  • Sex-linked

  • Sex-Modified/Sex-Influenced

  • Chromosomal

  • Sex Chromosome

  • Recessive disorders

  • Dominant disorders

Sex linked1

  • Gene expressed usually in one sex

  • Hemophilia – failure of blood to clot

  • Deuteronopia (color blindness)

  • Muscular Dystrophy – wasting away muscles

For our reebops
For our Reebops

  • We would consider the trait of having legs this.

Dad Mom

The Two possible Male Offspring










B b


Sex modified sex influenced
Sex-Modified/ Sex-Influenced

  • Alleles (Not on the sex chromosomes) have a different way of expressing themselves between sexes.

  • Beards/ Mustache (Males= Dominant)

  • Breast development (Females= Dominant)

  • Pattern Baldness (Male= Dominant)

  • B1- Dominant Male: No hair (B1B1 and B1B2)

  • B2- Recessive Male: Hair (B2B2)

  • B1- Recessive Female: No hair (B1B1)

  • B2- Dominant Female: hair (B1B2 and B2B2)

What was our example of a sex modified trait in our reebops
What was our example of A Sex Modified trait in Our Reebops?

  • The Tail!

  • The reasoning is because the dominant allele codes for something different depending on if your male or female.

Chromosomal disorders
Chromosomal Disorders

  • Trisomic 13- Patau Syndrome – die w/in 6 months

    • rare

  • Trisomic 18- Edwards Syndrome- die w/in 6 months

    • rare

  • Trisomic 21- Downs Syndrome- will survive but with a less than normal lifespan.

    • 1/900

Sex chromosome
Sex Chromosome

  • Triple X (XXX)– Normal intelligence and are fertile.

  • Turner Syndrome (XO) – Short, sterile, undeveloped 2ndary sex characteristics.

  • Klinefelter Syndrome (XXY) – Long limbs, sterile, breast development, underdeveloped genitalia.

  • Extra Y Syndrome (XYY) - increased risk of antisocial behavior, fertile.

Recessive disorders
Recessive Disorders

  • Cystic Fibrosis- mucus clogs lungs, liver, and pancreas. Don’t survive adulthood.

  • Sickle cell anemia- Poor blood circulation. (8% African Americans)

  • Tay- Sachs- Deterioration of central nervous system in infancy and don’t last to adulthood.

  • Phenyl- Ketonuria- Failure of brain to develop in infancy, if untreated they don’t survive to adulthood.

Dominant disorders
Dominant Disorders

  • Huntington’s Disease- Gradual deterioration of brain tissue in middle age, shortened life expectancy.

Techniques for detecting genetic disorders
Techniques for detecting Genetic disorders

  • Pedigrees

    • Family history of a disorder

  • Genetic Counseling

Pedigrees 3 steps on how to read them
Pedigrees: 3 steps on how to read them

  • Sex-Linked?

    • Usually seen only in males because they have 1 X

    • If Autosomal should be = distribution between sexes

  • Dominant or Recessive?

    • Dom- every offspring that has it should have parent

    • Rec- parent is a hetero, normal but a carrier

  • Single gene or several?

    • If 1 gene, parent: offspring ratio should be 3:1 (25%)

    • If multiple, ratio and percentage should be lower

Genetic counseling
Genetic Counseling

  • Helps families understand the risk of passing the disorder on by analyzing pedigrees.

  • Can also see genetic makeup of embryo by using prenatal testing through karotyping.

    • Amniocentesis- withdraw fluid @ week 16 to check enzyme activities.

    • Chorionic villus sampling- part of placenta is tested early in pregnancy.

    • Ultrasound- detect size, position, sex, organ health

    • Fetoscopy- direct view of fetus

  • Gene Replacement- new technique for replacing bad genes for good genes.