mendel’s genetics

Mendel’s Genetics• Mendel’s research provided

the groundwork for our understanding of inheritance of traits.

Mendel’s Conclusions• Mendel's four conclusions – although there are exceptions, his

conclusions apply to plants, animals and humans! Many of our deadly diseases are found to be carried on one recessive allele.

• First Conclusion: biological inheritance is determined by factors that are passed form one generation to the next. Today we know these factors as genes.

• Second Conclusion: Principle of dominance – Some alleles (forms of a gene) are dominant and some are recessive. An organism with a dominant allele for a particular form of a trait will always have that form.

Mendel’s Conclusions• Third Conclusion: Mendel's Law of Segregation = Each pea

plant has 2 alleles (different forms of a gene) for each trait. One allele comes from each parent. This means, that during the formation of each gamete (egg and sperm), the two alleles must separate or segregate from each other. Each gamete only carries a single gene (allele).

• Fourth Conclusion: Principle of Independent Assortment -

genes for different traits can separate INDEPENDENTLY during the formation of gametes.

Real World Genetics

• MOST traits are not inherited in such a simple manner as shown by Mendel. For example: – Many traits are controlled by more than one gene– Many alleles are neither completely recessive nor

dominant• We now know a gene is actually a small

section of a DNA molecule.

Exceptions to Mendel

• Incomplete Dominance• Codominance• Multiple Alleles for a Trait• Multiple Genes for a Trait

Jackalope = cross between

a jack rabbit and an

antelope


• Incomplete dominance – neither allele is dominant. – For example: Red + White sometimes makes …

Incomplete Dominance

• What CONCEPT does red + white = pink appear to follow? __________________

• How does this differ from blending? • Genetics of four-o-clock flowers:

– R = red allele– W = white alleleRR = red flower, WW = white flower, RW = pink flower

Blending

Incomplete Dominance• Draw a Punnett Square showing a cross between a red flowering four

o’clock and a white flowering four o’clock.

• What are the phenotypes and genotypes of the offspring?

Incomplete Dominance• Phenotype: All of the

offspring are pink • Genotype: All of the

offspring are RW• Draw a Punnett Square

showing a cross between two pink flowering four o’clock.

• What are the phenotypes and genotypes of the offspring?


• Is this blending?• Why or why not?• Have the alleles

(R and W) been “blended away?”

• Now show a cross between a pink and white flower.

R W

R

W

RR RW

RW WW


• Each allele in the example provides instructions to a cell for making an enzyme.

• The R allele produces an enzyme necessary for the production of red pigment.

• The W allele produces an enzyme necessary for the production of white pigment.

• Both alleles are active in incomplete dominance.


• Codominance -neither allele is dominant or recessive.

• Example: – variety of cattle with all red hair = RR – variety of cattle with all white hair = WW

• A cross of a red cow with a white bull produces offspring (RW) that have both red and white hair

Codominance

• Other examples:

+ =

Codominance

• Other examples:

+


• Multiple alleles: More than two alleles exist for a trait--however, each individual still only has two alleles.


Example: Hair Color1. Some alleles, such as brown-ebony, produce enzymes with very high

activity, which in turn produce a large quantity of the brown pigment.

2. Some alleles, such as brown-Swedish-blonde, produce enzymes with very little activity, which in turn produce only a small amount of the brown pigment.

3. All alleles fall somewhere on a continuum, from no activity to very high activity--which geneticists refer to as an allelic series.

4. In hair color, alleles with more activity are dominant to alleles with less activity. More activity —› more pigment —› hair color phenotype.

• http://www.indiana.edu/~oso/lessons/Genetics/RealColors.html

Multiple Alleles for a Trait

• Example: Variations of a tabby cat


• Example: Human Blood Groups– Before the 1900’s people

thought all blood was the same. Fatalities resulted from

• Transfusions of animal blood into humans!

• Transfusions of some human blood to other humans


• It was then discovered there are different types of red blood cells.

• Human Blood Groups – Three alleles: A, B, O

Multiple Alleles – Blood Types

• What are all of the possible genotypes using these three alleles? (Hint: Remember each person only has two alleles for a trait!!)

AA AO BB BO AB OO


Genotypes Phenotypes• AA Blood

Type A • AO Blood

Type A• BB Blood

Type B• BO Blood

Type B• AB Blood

Type AB• OO Blood

Type O

Multiple Alleles – Blood TypesWhat is the difference between the phenotypes?

•Type A = contains one type of antigen

•Type B = contains a different type of antigen

•Type AB = contains both types of antigens

•Type O = does not contain any antigens

Multiple Alleles – Blood Types–Antigen: A foreign substance that triggers an

immune response (production of antibodies)–Antibodies: part of the body’s defense for fighting

off infection –Example: If a person has Type A blood, the antigen

on his blood cells is NOT foreign to him. the body does not produce antibodies.

–Example: If Type B blood is transfused into a person with Type A blood or Type O blood, the body will attack the new blood cells as though they are an infection!


• Which blood type shows codominance? _________

• Which blood type is the universal donor? _________

• Which blood type is the universal recipient?_________

AB

AB

O


• Blood types in the United States are more or less common based on race and ethnicity.

• However, Type O is most common among all groups and Type AB is least common.

Rh Factor • Research conducted on rhesus monkeys.• Rh is a protein either found in the blood Rh+

or absent Rh-.• The Rh factor follows dominant/recessive

patterns of inheritance.

Rh Factor

• Mother-fetus incompatibility occurs when the mother is Rh- (dd) and her fetus is Rh+ (DD or Dd).

• Maternal antibodies can cross the placenta and destroy fetal red blood cells. The risk increases with each pregnancy.

• Treatment: If you are Rh-, you will be given a shot of Rh immunoglobulin during pregnancy. It prevents the production of Rh antibodies.

Rh Factor

• Rh- : Found in 15% Europeans; 7% African Americans

• Set up two Punnett Squares showing a cross between a father who is Rh+ and a mother who is Rh-.

• What is the possibility of the Rh- mother producing a fetus that is Rh+?


• Complete Reading on Blood Types• Discuss articles with your group• Answer questions


• Multiple genes for a single trait: – Example: height. Height is made up of the length

of different sections of your body added together. Each section is controlled by a different gene.

– Example: Eye color in humans. Controlled by interactions of at least 3 different genes.

Multiple Genes for a Single Trait

• Skin color: – Scientists now believe that 3 genes control skin color.– You get 3 alleles from your mother and 3 alleles from your

father for 6 alleles. – If all 6 of the alleles are for dark skin, you will have the

darkest possible skin. – If you have 5 dark alleles and one light, you will have very

dark skin.– If you have all 6 light alleles then you will have the lightest

skin possible. – http://www.dep.anl.gov/


Complete Worksheets in Groups

mendel’s genetics

Documents

red white

white flowering

r allele

dominant allele

recessive allele

red hair

red flowering

white allelerr