Sex Linked Traits
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Traits controlled by genes located on sex chromosomes
Genes on the X-chromosome are called _________________
Since males only have one X-chromosome, they are often affected by recessive X-linked traits more
than females
Females have a second X-chromosome that may “________” the
recessive trait
Ex. Red-Green Colour Deficiency
• Recessive X-linked trait
• 8-10% of males have this deficiency
• Ex. Mother is a carrier for the colour deficiency
• Dad does not have the gene for colour deficiency
• Only possibility is for a male (XY) child to have this deficiency!
• As a result, very rare in females
Multiple Alleles
• The traits we have studied so far have all been controlled by one gene with two alleles
• Many traits are the result of the interaction between _________________________ for one gene –
multiple alleles
• This is why for some traits, there are more than just two options
Ex. Blood Types
• In humans, a single gene determines a person's ABO blood type
• This gene determines which type of ___________ protein, if any,
is attached to the cell membrane of red blood cells
• An antigen is a molecule that stimulates the body's immune
system
• There are three common alleles: ______, ______ and ______
• The combinations of these three alleles produce _____ different
phenotypes, commonly called blood types
• Blood Types:
• A – IAIA or IAi - dominant
• B – IBIB or IBi - dominant
• AB – IAIB
• O – ii – recessive
• The IA allele has an A antigen, IB a B antigen, and i has
__________________
• No antigen = blood can be donated to any other blood type ______________ donor if type O
Ex. Rabbit Coat Colour
• Four alleles: Agouti ______, Chinchilla _____, Himalayan _______ and Albino _________
• Order of dominance:
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Problem:
• A man has type O blood and a woman has type B blood – what possible blood types could their
children have? If the couple has six children, all with type B blood, what could you infer about the
woman's genotype?
• Parent genotypes: Dad must be _______, mom could be ______ or ______
• Perform two crosses to determine possibilities
Results:
Polygenic Inheritance
• There are traits that exhibit what is called _____________ __________________ – a range of
variations within one trait
• For example, skin colour or height in humans
• Continuous traits occur over a ______________ - people cannot be categorized as one thing or another
• Traits that exhibit this variation are controlled by more than one gene, and are called _____________
____________
• A group of genes that all contribute to the same trait is called a ______________
• Each dominant allele contributes to the trait, while recessive alleles do not contribute to the trait
• Ex. The more dominant alleles one has for skin colour, the darker the skin will be