10.2 inheritance Flashcards
what are LINKED gene loci?
linked genes – genes found on the SAME CHROMOSOME
the closer the loci of two linked genes,
the less frequently they are separated by crossing over
how do linked genes affect each other during allele inheritance
the allele inherited for one gene does NOT affect which allele will be inherited for the other gene
how are recombinants involving linked genes drawn?
t b (one chromosome)
one loci
each letter codes for a different trait
two distinct possibilities for the genotype of a heterozygous parent in a LINKAGE PROBLEM (linked genes)
tb
and
tB
how to test for linkage (test cross)
heterozygous parent x homozygous recessive parent
- not linked: follow mendels law of indep assortment, 1:1:1:1
- non-mendelian ratios obtained, genes likely to be linked
during a test cross to test for linkage, the lower the recombinant frequency,…
the closer the linked genes are on the chromosome
what is sex-linkage
any gene found on the sex chromosomes
what is autosomal linkage
two genes found on the same autosomal chromosome (a non-sex chromosome)
test for recombinant phenotypes
test cross (homozygous recessive for both traits)
polygenic traits
more than one gene may affect a single trait
pleiotropic genes
a single gene may affect multiple traits
epistatic genes
a gene may impact the expression of another gene
penetrance of the allele
some alleles are not expressed in all individuals
expressivity of the allele
some alleles are expressed with varying intensity
law of independent assortment
unlinked genes segregate independently (As a result of meiosis)
what did thomas hunt morgan discover
non-mendilian ratios in Drosophila (fruit flies as a model organism)
LINKED GENES
(Eg eye colour and wing development)
why druit flies as a model organism for mendilian ratio discovery
- small, compact
- reproduce fast
- distinct male and female
- short life cycle
- produce hundreds of offspring
what is a dihybrid cross?
the genetic crossing of two organisms that examines the inheritance of two different traits, each controlled by separate genes
what is the law of independent assortment
unlinked genes segregate independently as a result of meiosis
what did morgan observe in the flies
red eyes vs white eyes
- observed a male with white eyes (instead of red)
how is the most common allele of any trait represented
+
eg heterozygous
Cy/+ or Cy+ Cy
how are mutant alleles represented
one / a few letters
what is autosomal linkage
2 genes found on the same autosomal chromosome
2 reasobs for non-mendilian ratios
- sex linkage (gene on sex chromosomes)
- autosomal linkage (2 genes on same autosomal chromosome)
continuous variation
a range of phenotypes – also affected by environment
eg height in humans
what is the purpose of the chi-squared test
assess the degree of difference between expected and observed results
