Bio- Modern Genetics

• Secret of life: sequence of bases in DNA that code for the sequences of amino acids in proteins

• Multiple genes can be on the same chromosome

Chromosome Theory

• Walter Sutton 1902

• Theory- genes are located on chromosomes, each gene occupies a specific place on a chromosome

• called the spot where the genes are the locus

• gene may occur in several forms but each chromosome has only 1 allele for each gene

Comparing Theory to Mendel

• genes and alleles- genes are located on chromosomes

• dominance and recessive- recessive has the lack of a dominant trait

• Segregation- pairs of chromosomes separate when gametes form

• Independent assortment- separation of the chromosomes and chromatids are separate

Linked Genes

• are inherited together

• do not undergo independent assortment

• genes on the same chromosome

• Thomas Hunt Morgan

  • fruit flies- ideal for genetic studies

  • grey body is dominant to black

  • normal wings are dominant to small

Morgan Experiments

• crossed purebred gray normal wings with purebred black small wing flies

• all in F1 are gray with normal wings

• did a test cross with F1

  • test cross- when an unknown organism is crossed with heterozygous recessive

• 25% for each phenotype- expected

• observed 41.5 gray normal and black small

• 8.5 gray small and black normal

• significant difference

• concludes that the gene for body color and wing size are linked

  • do not assort independently

  • on the same chromosome

Linkage Groups

• groups of genes that are inherited together

• fruit flies have 4 linkage groups

• have 4 pairs of chromosomes

• corn has 10 linkage groups

• have 10 pairs of chromosomes

Crossing Over

• produces individuals with rearranged linkage- recombinants

• frequency of crossing over can be used to map genes

Sex Determination

• Autosomes- homologous pairs of chromosomes

• sex chromosomes are not necessarily homologous X or Y

  • determines the sex of an individual

  • XX= Female, XY= Male

Sex Linkage

• genes on sex chromosomes are sex linked

• usually the X chromosome

• recessive X linked traits are more expressed in males

  • no other X to potentially have a dominant allele

Morgan Experiments

• gene for eye color is located on the X chromosome

• red dominant to white

• white eyed male with homozygous red eyed female

  • all have red in F1

  • white only appears in F2 in males

Gene Interactions

• incomplete dominance- active allele does not completely compensate for an inactive allele

  • Carnations- red x white= pink, pink x pink= ¼ red, ¼ white, ½ red

• Codominance- both alleles are expressed

  • cattle- white x red= roan, roan x roan= 1 white, 2 roan, 1 red

Polygenic Inheritance

• trait is controlled by many genes

• tends to follow a gradient not either or

  • height

Human Blood Groups

• A

  • antigen- A

  • antibodies- anti B

  • Possible genotypes- I^A I^A , I^A i

• B

  • antigen- B

  • antibodies- anti A

  • Possible genotypes- I^BI^B , I^B I

• AB

  • antigen- A and B

  • antibodies- neither

  • Possible genotypes- I^AI^B

• O

  • antigen- neither

  • antibodies- anti A and anti B

  • Possible genotypes- ii