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.