How is genetic information passed? Thought 1- The Homunculus- tiny,
complete person inside a sperm that grows into a full grown person
Thought 2- Blended Heredity-
Then comes Mendel…..
Gregor Mendel- 1860’s - Austrian monk
Worked with Pisum sativum (pea plants)- interested in statistics of inheritance
Never knew of genes or DNA
Just lucky!!
Why peas?
Small Easy to grow many offspring mature quickly 7 identifiable traits can be self- and cross-
fertilized
What is a trait?
TRAIT: the physical effects of the expression of a gene• the hair is blonde• the bunny has spots• The cat has white feet
Fig. 11.21, p. 191
Traits Mendel Chose to observe 1.)Flower color 2.)Seed Color 3.) Seed shape 4.) Pod Color 5.) Pod shape 6.) Flower position 7.)Plant height
Each trait shows as 1 thing or another
i.e.- flowers either purple or white
pods either inflated or wrinkled
Trait Studied DominantForm
RecessiveForm
F2 Dominant-to-Recessive Ratio
SEED SHAPE
SEED COLOR
POD SHAPE
POD COLOR
FLOWER COLOR
FLOWER POSITION
STEM LENGTH
2.96:1
3.01:1
2.95:1
2.82:1
3.15:1
3.14:1
2.84:1787 tall 277 dwarf
651 long stem 207 at tip
705 purple 224 white
152 yellow428 green
299 wrinkled882 inflated
6,022 yellow 2,001 green
5,474 round 1,850 wrinkled
Fig. 11.5, p. 178
Mendel’s Experiment
3 Steps Step 1- Create purebred parental generation
Allows self-fertilization for many generations to get purebred white and purebred purple flowering plants
PUREBRED: organism which has the same traits as both parents
Yorkshire Terriers, Dalmatians, etc.
STEP 2
Creates the F1 generation- First filial- latin for son or daughter
Crosses Purple plant x White Plant
Results- All had purple flowers!!!!!
STEP 3
F2 Generation Crosses 2 F1 plants F1 x F1 (purple
x purple) Results--- 3:1 ratio of purple to white!
What’s an allele?
ALLELE: a version of the expression of a gene
• all genes have 2 alleles for their expression
• a brown eyed person may have 2 “brown” alleles or 1 “brown” and one “blue” allele
Mendel Summarizes Data 1) parents must transmit a “factor” containing information- we know
these as genes now
2) Different forms of “factors”= ALLELES• Genetic makeup of all alleles= genotype• Physical appearance due to alleles= phenotype
3)Dominant alleles mask recessive alleles
4) Everyone has two factors-1 from each parent- if they are the same= homozygous, if they are different= heterozygous
DOMINANT: gene that is fully expressed when two alleles are paired
RECESSIVE: gene that is not expressed when paired with a dominant gene or that produces a different version of the trait than the dominant
Which one is dominant? Brown eyes or blue? a person with 2 “brown” alleles has
brown eyes a person with 1 “brown” and 1
“blue” has brown eyes or a person with 2 “blue” alleles
has blue eyes
LAW OF DOMINANCE - the dominant allele is expressed and the recessive allele is hidden, if a dominant allele is not present, the recessive will be expressed
MENDELS LAWS/modernized LAW OF SEGREGATION- during
meiosis, gene pairs separate and end up in individual gametes
LAW OF INDEPENDENT ASSORTMENT - during meiosis, traits will sort independently of each other
Revisiting Law of Segregation
AA
AA
AA
AA
AA
A A A A a a a a
aa
aa
aa
aa
aa
Aa
Fertilizationproducesheterozygousoffspring
meiosisII
meiosisI
(chromosomesduplicated
before meiosis)
Homozygousdominant parent
Homozygousrecessive parent
gametes gametes
Fig. 11.4, p. 178
Revisiting Law of Independent Assortment
Fig. 11.8, p. 180
Nucleus of a diploid (2n)reproductivecell with only two pairs ofhomologouschromosomes OR
Possible alignmentsof the homologouschromosomes atmetaphase I ofmeiosis, as shownby two diagrams:
The resultingalignments ofchromosomes atmetaphase II:
The combinationsof alleles possiblein the forthcominggametes:
1/4 AB 1/4 ab 1/4 Ab 1/4 aB
A A A A
A A A A
AAAA
B B
B B
BB
B B
BBBB
a a a a
aa aa
aaaa
bb b b
bb b b
b b b b
Chromosome Theory of Heredity
the material of inheritance is carried by genes on chromosomes, and the genes occur in pairs on homologous chromosomes
the gene pairs can be found in different types called alleles and are found at the same place on each chromosome, called the LOCUS
Fig. 11.3, p. 177
A pair of homologous chromosomes,each in the unduplicated state (mostoften, one from a male parent and itspartner from a female parent)
A gene locus (plural, loci), thelocation for a specific gene ona specific type of chromosome
A pair of alleles (each being acertain molecular form of a gene)at corresponding loci on a pair ofhomologous chromosomes
Three pairs of genes (at threeloci on this pair of homologouschromosomes); same thing asthree pairs of alleles
BASIC GENETIC SHORTHAND
in working with genes, scientists have found that assigning alphabetical letters to each trait makes the traits easy to follow through generations
Rules: Dominant alleles are written as
CAPITAL letters Recessive alleles are written as
lower case letters Traits are expressed in pairs, so
the diploid condition will always have 2 of the same letters representing the trait
examples include BB, Bb, bb
REVIEW
GENOTYPE - the types of genes an organism has, expressed in letters
PHENOTYPE - the physical expression(appearance) of the gene pair
HOMOZYGOUS - a genotype description of a gene pair with both dominant or both recessive alleles
HETEROZYGOUS - a genotype description of a gene pair with 1 dominant and 1 recessive allele in the gene pair
Example of Genetic Law In peas, yellow pea color is dominant
over green pea color. Just because it is more commonly seen,
does not mean that trait will be the dominant trait
Phenotype Genotype Genotypic
Expression
Yellow Pea BB Homozygous dominant
Yellow Pea Bb Heterozygous
Green Pea bb Homozygous recessive
Ideas to Keep In Mind… it is simpler to discuss one gene pair at a time
an organism will have many traits expressed at the same time
not all genes are expressed by 2 alleles, some may be expressed by multiple alleles, like blood type
not all traits are expressed by just one gene, some may involve many genes like skin color-determined by the expression of 21 different gene pairs
MAKING PREDICTIONSUSING GENES To improve crops
To help produce an improved product people will buy
To predict possibility of genetic disorders
Paternity Tests
HOW TO PREDICT use of PUNNETT SQUARES
MONOHYBRID CROSSES• one trait being crossed• use 4 squares
DIHYBRID CROSSES • two traits being crossed• use 16 squares
In the Hairy Apeloideus, blue ears are dominant to red ears. If a heterozygous individual is crossed with an red eared individual, what is the probability that the offspring will have red ears?
DIHYBRID CROSSES 2 Factors Example- In Humans curly hair (C ) is dominant to
straight hair (c) and freckles (F) are dominant to not having freckles (f). If a man who is heterozygous for curly hair and doesn’t have freckles marries a woman who has straight hair & is homozygous dominant for freckles, and they have babies, what could the possible phenotypes in their offspring be??
Completing the Cross
1- Figure out gametes- use the FOIL method- SEE BOARD
2- Write gametes above and on side of boxes- use 16 squares this time
3- Letter pairs go back together in offspring
Completing the Cross
1. Determine the letter you’ll use
2. Determine the gametes of the parents
3.Make your punnett square
DIFFICULT PREDICTIONS Mendel was lucky because his
“factors” behaved in a predictable fashion and there were only 2 phenotypes per trait
Not all traits are so orderly
Incomplete Dominance
the genes in the pair are not necessarily dominant or recessive, but become “BLENDED” in the offspring
heterozygotes show the blending, homozygotes show one of 2 expressions
Examples in Humans
Familial Hypercholesterimia- caused by defective proteins that cannot remove LDL from blood- leads to atherosclerosis-
Sickle Cell Anemia
CODOMINANCE
both genes become expressed, but are individually recognizable
may involve multiple alleles
ROAN Animal Coats
Red haired parent + White haired parent = red and white haired offspring
(Roan- horses and cattle)
Examples in humans
Tay-Sachs disease- in children- fat buildup on brain
Gene is recessive but heterozygotes have good and bad enzymes present- but they’re normal
Blood Types A, B, AB, O- different antibodies present on RBCs
Other Influences Polygenic traits have more than
one gene pair controlling expression
Pleiotropy occurs when a single gene affects more than one trait
Multiple Alleles have more than 2 phenotypes expressed
Blood Type Genetics
Blood is …• 1. Plasma• 2. Cells
• a. Platelets• b. white blood cells• c. Red blood cells
Blood Type genetics
Genes involved
I = dominant i = recessive
Rather than just 2 alleles, there are many
Blood Type Genetics Red Blood cells contain surface antibodies(like
little flags)- marker proteins A blood contains A proteins and anti- B antibodies
B blood contains B proteins and anti- A antibodies
O blood contains no proteins and anti- A and anti- B antibodies
AB contains A and B proteins but no antibodies
http://learn.genetics.utah.edu/units/basics/blood/types.cfm
Blood Type genetics
Antibodies recognize foreign blood and cause agglutination (clumping)
Transfusions- example- person with Type A blood must be matched with A or O ; otherwise Anti B antibodies will recognize B blood and reject it
Type 0 = universal donor Type AB = universal receiver
PROBLEM
If a man with O blood type marries a woman with type AB blood, what blood types are possible in their children?
X or Sex Linked Traits
The X Chromosome is bigger when compared with the Y chromosome
Females= XX Males = XY Some traits are only carried by Genes on
the X chromosome Men need only 1 copy, women need 2 to
exhibit the trait
Example
Hemophilia- failure of blood to clot XH = normal Xh= hemophilia Women need 2 copies of Xh
Men only need 1 copy See example on board
Other sex linked traits
Red-Green Color Blindness Congenital Night Blindness Duchenne Muscular Dystrophy
Environmental Influences such as weather may affect the phenotypic expression of the organism (will have multiple alleles)
PEDIGREES allows you to show how a trait and the
genes that control it are inherited within a family or group
used to study familial inheritance
could be used for genetic counseling for parents who are afraid of passing on a devastating genetic disorder
Fig. 12.11, p. 202
male
female
marriage/mating
Individual showingtrait being studied
sex notspecified
generationI,II, III, IV...
offspring in order ofbirth, from left to right
I
II
III
IV
V
6 7
12
5,56,6
5,56,6
5,56,6
5,56,6
5,56,6
5,56,6
6,65,5
6,65,5
5,66,7
6,66,6Gene not expressed in this carrier.