4. Linkage Flashcards
Female chromosomes
XX
Male chromosomes
XY
How would you work out the probability of producing a certain gender with particulate genotype.
Boy with blue eyes .
Work out probability of child having blue eyes and then decide it by 2.
Sex linked characteristics
Alleles that code for them are located on sex chromosomes.
Y Is smaller then X so carries fewer genes - more genes carried on X chromosome (X-linked genes)
Why are males more likely than females to show recessive phenotypes for genes that are sex linked?
They only have one X chromosome and often have one allele for sex linked genes.
So because they only have one copy, they express the characteristic of the allele even it’s it’s recessive
Name 2 genetic disordered caused by faulty alleles on sex chromosome
Colour blindness
Haemophilia
Both carried on X chromosome song they’re X linked disordered
Y linked disorders do exist just not as common.
How is the faulty allele for colour blindness represented
XnY
Y chromosome doesn’t have allele for colour vision so it’s just represented by Y
Colour blindness
Females would need 2 copies of recessive allele to be blind on the 2 X chromosomes as it’s an X linked disorder.
Yet males only need one as they only have one X chromosome
More common in men
Females with one copy of allele are carriers
Carrier
Person carrying an allele which is not expressed in phenotype but can be passed onto offspring.
Why can’t males be carried of colour blindness ?
Or x linked disorders
They only have one copy of the chromosome X so if they have the allele they will have the diseases - whether it’s recessive or not
Autosome
Any chromosome that isn’t sex chromosome.
Autosomal genes
Genes located on autosomes.
Genes on same autosomes are said to be linked because they stay together during independent segregation of chromosomes in meiosis 1.
Alleles will be passed onto offspring together
(Only reason this won’t happen is if crossing over splits them apart) was
Closer together 2 genes are on autosome …
More closely linked
As crossing over less likely to spilt them up
Independent segregation
Random division of homologous chromosomes into depart daughter cells dying meiosis.
Crossing over
When 2 homologous chromosomes swap bits
Meiosis 1 before independent segregation
