Mendelian Genetics

Fig. 11.20, p. 190

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.

PARENTAL (P) Generation

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

Blood Types• A• B• AB• O

Genotypes IAIA or IAi IBIB or IBi IAIB

ii

http://anthro.palomar.edu/blood/table_of_ABO_and_Rh_blood_type_frequencies_in_US.htm

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?

THE PAURY MOVICH SHOW

TODAY’S SHOW:“I AM NOT THE FATHER!”

THE PAURY MOVICH SHOW

Next Week’s Show- My Dad is an Alien!

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.