BIOL 211 - CELLULAR AND ORGANISMAL BIOLOGY

Lecture Outline for March 2, 2005

 

Topic: multiple alleles, dominance relationships, sex linkage

Chapter 10 – a small part of section 10.3; Chapter 11 sections 11.1, 11.2, 11.4

Figures used in lecture: 10.17, 10.18, 11.10

Additional Resources

            Gene Interactions – covers multiple alleles, codominance, incomplete dominance, and sex linkage

 

NOTE: The monohybrid cross and dihybrid cross material covered in class to day is contained in the Lecture Outline for Monday February 28th.  The Lecture Outline below covers “non-Mendelian” genetics only.

 

Key Terms

self-fertilize (self-pollinate), true-breeding, P generation, F1 generation, F2 generation, gene, allele, homozygous, heterozygous, dominant, recessive, genotype, phenotype, monohybrid cross, Punnett square, test cross, dihybrid cross, 9:3:3:1 ratio

 

Multiple Alleles

the ABO blood group system in humans is determined by a set of 3 alleles at one gene

any individual has only 2 alleles – one on each homologous chromosome

these alleles combine to form 4 different phenotypes: A, B, AB, O

Phenotype

Genotypes

Antigens Produced

Antibodies Produced

Compatibility

A

IAIA , IAIO

A

anti-B

 

B

IBIB , IBIO

B

anti-A

 

AB

IAIB

A , B

none

universal recipient

O

IOIO

none

anti-A, anti-B

universal donor

For the following problems state whether the child mentioned can actually be produced from the marriage.  EXPLAIN YOUR ANSWER.

1. An O child from the marriage of two A individuals.

 

2. An A child from the marriage of an A to a B.

 

3. An O child from the marriage of an AB to an A.

 

 

Dominance Relationships

Not all alleles have a distinct dominant-recessive relationship.

Define AND BE ABLE TO GIVE AN EXAMPLE OF: codominance, incomplete dominance

codominance:

 

example of codominance =

 

incomplete dominance:

 

example of incomplete dominance =

 

 

Sex Linkage

Define: wild type, mutant phenotype, linked genes, sex chromosomes, sex-linked genes, autosomes

 

linked genes:

 

sex linked genes:

 

autosomes:

 

wild type:

 

mutant:

 

 

Thomas Hunt Morgan and Drosophila (fruit flies)

In Drosophila, gender is determined the same way as in humans

XX =  female and XY =  male

 

Drosophila eye color - r+ = wild type = red eyes

                                    r =  mutant = white eyes

P          red eyed female (r+r+)   X   white eyed male (rY)

F1         all red eyed  - females are r+r, males are r+Y

F2         3 red : 1 white

    

         r+

         r

r+

       r+r+

  red female

       r+r

  red female

Y

       r+Y

   red male

       rY

 white male 

 

            by gender:        all females have red eyes

                                    ½ males have red eyes

                                    ½ males have white eyes

 

Sex-Linked Genes in Humans

red-green color blindness

hemophilia A

1.  phenotype is seen more often in the males than the females

2.  a male with the mutation passes the mutant allele only to his daughters

3.  heterozygous females are carriers

4.  mutant phenotype can skip a generation

 

For the trait of colorblindness:

parents are:     normal female   X   normal male

children are:          1 son with normal vision

                1 son is colorblind

What % of daughters will be colorblind?