The Chromosomal Theory of Inheritance:

• Chromosomes and genes are present as ______________________

• homologous chromosomes ___________during meiosis

• ________________ restores chromosome number to ____________________

• The _________________________ claims it is the chromosome that ___________ and _________independently.

• In flies ________________ is dominant to ______________, and long wings _____________ are dominant to vestigial wings _____.

• What is the expected phenotypic ratio from a cross between a heterozygous gray, heterozygous normal winged fly with a black vestigial fly?

• ________________________

• But what he got was…..

Gene Linkage

• What explains the non-Mendelian results?• __________________________________• The traits are located on the _________________

and are _________ to each other that they are said to be ___________.

• If the traits are linked, then all of the offspring should resemble the parental types, black vestigial or gray normal.

• How did we get the recombinant traits of black, normal and gray vestigial?

Using Recombination Frequency to Map Traits

• _______________________ between black and vestigial traits is __________

• Recombination frequency between cn and black is __________

• Recombination between cn and vg is _________________

• Map these traits on the chromosome.

• Determine the order of genes along a chromosome based on the following recombination frequencies:

• A - B 8%

• A - C 28%

• A - D 25%

• B - C 20%

• B - D 33%

• _______________

Chromosome Types• Autosomes are the first

________________________________________________________________

• Autosomes do not determine ________

• Sex chromosomes are the _________

• In males, the sex chromosomes are _____

• In females, the sex chromosomes are _________

Sex Linked Traits• Drosophila eye color is linked on the

_______________________• Females carry ____________ of the gene while males

have only _________• The _____ chromosome does not carry many sex-linked

traits at all!• White eyed females carry the recessive allele on

_______________• Red eyed females can be _______________________• White eyed male cannot hide the trait since he has only

one _______.

Morgan and

Linked Traits

• Who is responsible when a boy inherits a sex linked condition?

• A carrier of a condition is heterozygous for the trait, so only____________ can carry sex linked traits.

Human Sex-linked traits:

• Red-green colorblindness

• Hemophilia

X Inactivation in Females• How does an organism compensate for

the fact that females have a double dosage of sex-linked genes, while males have only one?

• The inactivation is random and approximately half the X’s from Mom and half the X’s from Dad will inactivate

• The calico cat is the result of multiple alleles on the X chromosome combined with X inactivation.

• One allele causes orange fur and the other causes black fur.

• The male cat will be either orange or black.

• Only a heterozygous female will be calico with regions that are orange and regions that are black based on the X inactivation.