Linkage and Epistasis Flashcards
What is the difference between X and Y chromosomes?
Y chromosomes produce the male sex.
They have a different shape to X chromosomes.
What are genes located on the sex chromosome called?
Sex linked
Compare the sizes of the X and Y chromosome.
The X chromosome is much larger than the Y chromosome.
What are homologous/non homologous sections on the X and Y chromosome? What does this mean for alleles?
Homologous regions have a complimentary region on the X and Y chromosome. This means there will be 2 alleles present for a gene.
Non homologous regions on the X chromosome will not have a complimentary region on the Y chromosome because it does not exist (as the Y chromosome is smaller). Therefore, only one allele for a gene will be present.
What type of genes do non homologous regions on sex chromosomes contain?
Sex determining genes.
In the non homologous region on the X chromosome, why will any genes in this region always be displayed in males?
There is no complimentary region on the Y chromosome that could mask this trait (using a dominant allele for example, if the one on X is recessive), so the trait on the X chromosomes is always displayed.
What are X linked genetic disorders?
A genetic disorder caused by a gene on the X chromosome.
Why are genetic diseases, such as haemophilia, most common in men?
They are caused by recessive genes on the X chromosome. Because men have a smaller Y chromosome, there will be only one allele present which will be on the X chromosome, therefore there is no chance that a dominant allele will be present to mask this recessive gene on the Y chromosome, so the disease is caused.
What is haemophilia?
A genetic disease caused by the presence of a recessive gene. It lead to excessive bleeding as the blood is unable to clot.
What are autosomes?
Any chromosomes that are not sex chromosomes.
Define autosomal linkage.
Where 2 or more genes carried on the same autosome do not assort independently in meiosis.
With autosomal linkage, why do we not get the phenotypic ratio that we would normally expect?
There is no crossing over of genes in meiosis so all of the linked genes remain together.
With autosomal linkage, which law do genes not follow?
Law of independent segregation.
How many gametes can be produced from 2 homologous pairs of chromosomes?
4 gametes.
Define epistasis.
When 1 gene locus masks or modifies the phenotype produced by the second gene locus. One gene alters the expression of others.
