Linkage - Sex, Autosomal & Epistasis Flashcards
(26 cards)
What is a karyotype
A visual representation of an individuals chromosomes, arranged by shape and size
What are the 2 types of sex chromosomes
X and Y
What are the chromosomes required for a female? What is this called
XX
Homogametic
What are the chromosomes required for a male? What is this called
XY
Heterogametic
Which chromosome has fewer alleles
Y chromosome
Where are genes carried
Genes are carried on both the X or Y chromosomes
What are some parts on the X chromosome
Some parts are unpaired
When is a gene classed as sex linked
When a gene is located on the unpaired part of the X chromosome
What must a carrier be
Heterozygous - they CARRY the recessive allele but don’t have the condition
What is autosomal linkage
Where 2 genes are found on the same chromosome so are therefore said to be linked
What is epistasis
Where the expression of one gene affects the expression of another
What is Mendel’s law of independent assortment
For unlinked genes, either allele in a pair can combine with either allele in another pair
This means that we can have 4 different combinations of alleles in these gametes
When does a 9:3:3:1 ratio occur
When 2 heterozygous parents with unlinked genes are crossed
Why would we ever not get the ratio that we expect
Because crossing over or autosomal linkage has occurred
When does a 1:1:1:1 ratio occur
When a heterozygous and homozygous recessive individuals are crossed
What are linked genes
Genes that are located close together on the same gene
What will happen if genes are linked? Why
They are likely to be inherited to be linked together, because they are physically linked and genes on the same chromosome are usually passed down as a unit in meiosis
So if an individual inherits one, it is likely to inherit the other too
When does a 3:1 ratio occur
When 2 individuals which are heterozygous for 2 linked genes are crossed
Why are the ratios for heterozygous linked and unlinked genes so different
Because the linked genes are inherited together so do not obey Mendel’s law of independent assortment
What is a recombinant
An individual with different phenotypes from the parents
When is crossing over more likely to occur
When the 2 genes are further apart on the chromosome
When/how do recombinants get made
They get made when parent alleles are shuffled due to crossing over, creating new combinations of alleles
What is the equation for recombination frequency
Recombination frequency = (number of recombinant offspring) / (total number of offspring) X 100
What is the maximum % of recombination frequency that we can get? Why
50%
Because a % of over 50 means that the genes are not linked so the 2 pairs must be on different pairs of homologous chromosomes and so Mendel’s law of independent assortment will be obeyed
