inheritance 3.7 Flashcards
define genotype
the genetic constitution of an organism
define phenotype
the expression of an organism’s genetic constitution
combined with it’s interaction with the environment
define allele
different forms of a particular gene
found at same locus on a chromosome
a singe gene could have many alleles
how many alleles per gene do diploid organisms carry
2
define dominant allele
an allele whose characteristic will always appear in the phenotype
whether one or two are present
define recessive allele
an allele whose characteristics only appear in the phenotype if no dominant allele is present
meaning two must be present
define codominant alleles
two dominant alleles that both contribute to the phenotype
either by showing a blend of both characteristics
or the characteristics appearing together
homozygous
both alleles are recessive
or both are dominant
heterozygous
one allele is dominant
the other is recessive
define monohybrid inheritance
where one phenotypic characteristic is controlled by a single gene
how to draw a genetic diagram
parental phenotypes
parental genotypes
gametes
offspring genotypes
punnet square
offspring phenotypes ratio
define dihybrid inheritance
where two phenotypic characteristics
are determined by two different genes
present on two different chromosomes at the same time
how to draw a dihybrid cross with parental phenotypes RrGg and RrGg
RG Rg rG rg
RG
Rg
rG
rg
define sex-linkage
where an allele is located on one of the sex chromosomes
meaning it’s expression depends on the sex of the individual
why are males more likely to express a recessive sex-linked allele
most sex linked alleles are located on the X chromosome
therefore males only get one copy of the allele
so will express this characteristic even if its recessive
females get two alleles so this is less likely
which parent do males inherit sex-linked characteristics from
mother
Y chromosome can only come from their father
male chromosomes
XY
female chromosomes
XX
define autosomal linkage
where two or more genes are located on the same (non-sex) chromosome
only one homologous pair needed for all four alleles to be present
punnet square to show sex linked cross with parental genotypes XHXh XHY
XH Xh
XH
Y
punnet square to show a multiple alleles cross with parental genotypes of IAIO and IBIO
IA IO
IB
IO
define epistasis
where two non-linked genes interact,
with one gene either masking or suppressing the other gene
recessive epistasis
where two homozygous recessive alleles mask the expression of another allele
dominant epistasis
where one dominant allele masks expression of multiple other alleles
