genetics, populations, evolution and ecosystems Flashcards
genotype
genetic constitution of an organism (alleles it has for a gene)
phenotype
expression of genes and their interaction with the environment
allele definition
different versions of a gene found at the same locus on a chromosome
dominant allele definition
an allele that will always be expressed in the phenotype
recessive allele definition
an allele that is only expressed in the phenotype if no dominant allele is present
homozygous definition
a pair of homologous chromosomes carrying the same alleles for a single gene
heterozygous definition
a pair of homologous chromosomes carrying two different alleles for a single gene
codomiant alleles definition
both alleles are equally dominant and expressed in the phenotype
monohybrid inheritance definition
one phenotypic characteristic is controlled by a single gene
dihybrid inheritance definition
two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time
sex-linkage definition
a gene whose locus is on the X chromosome
multiple alleles definition
more than two alleles for a single gene
autosomal linkage definition
genes that are located on the same chromosome
epistasis definition
when one gene modifies or masks the expression of a different gene at a different locus
expected ratio of monohybrid cross of two heterozygous alleles
3:1
why are males more likely to express a recessive sex-linked allele?
- most sex-linked alleles on X chromosome
- males only have one X chromosome
- so only carry a single allele
- whereas women must be homozygous recessive
which parent do males inherit sex-linked characteristics from?
their mother as she has the X chromosome, if she is heterozygous for sex-linked alleles, she is a carrier
what is recessive epistasis?
where two homozygous recessive alleles mask expression of another allele
what is dominant epistasis?
where one dominant allele masks the expression of other alleles
ratio of recessive epistasis
9:3:4
ratio of dominant epistasis
12:3:1
expected ratio of dihybrid cross
9:3:3:1
what are the two only possible gametes for cases of autosomal linkage?
homozygous dominant or recessive
when does autosomal linkage produce 4 gametes?
when crossing over has occured
gene pool definition
all of the alleles of all the genes within a population at one time
allele frequency definition
the proportion of an allele in a gene pool
what is the hardy-weinberg principle?
allows us to estimate allele frequency and if the frequency is changing
assumptions of the hardy-weinberg principle
- no mutations
- no migration
- no selection
- random mating
- large population
two hardy-weinberg equations
p+q=1
p2+2pq+q2=1
what does p equal in H-W?
frequency of the dominant allele