Generalizations Hardy–Weinberg principle
1 generalizations
1.1 generalization more 2 alleles
1.2 generalization polyploidy
1.3 complete generalization
generalizations
the simple derivation above can generalized more 2 alleles , polyploidy.
generalization more 2 alleles
punnett square three-allele case (left) , four-allele case (right). white areas homozygotes. colored areas heterozygotes.
consider allele frequency, r. two-allele case binomial expansion of (p + q), , three-allele case trinomial expansion of (p + q+ r).
(
p
+
q
+
r
)
2
=
p
2
+
q
2
+
r
2
+
2
p
q
+
2
p
r
+
2
q
r
{\displaystyle (p+q+r)^{2}=p^{2}+q^{2}+r^{2}+2pq+2pr+2qr\,}
more generally, consider alleles a1, ..., given allele frequencies p1 pn;
(
p
1
+
⋯
+
p
n
)
2
{\displaystyle (p_{1}+\cdots +p_{n})^{2}\,}
giving homozygotes:
f
(
a
i
a
i
)
=
p
i
2
{\displaystyle f(a_{i}a_{i})=p_{i}^{2}\,}
and heterozygotes:
f
(
a
i
a
j
)
=
2
p
i
p
j
{\displaystyle f(a_{i}a_{j})=2p_{i}p_{j}\,}
generalization polyploidy
the hardy–weinberg principle may generalized polyploid systems, is, organisms have more 2 copies of each chromosome. consider again 2 alleles. diploid case binomial expansion of:
(
p
+
q
)
2
{\displaystyle (p+q)^{2}\,}
and therefore polyploid case polynomial expansion of:
(
p
+
q
)
c
{\displaystyle (p+q)^{c}\,}
where c ploidy, example tetraploid (c = 4):
depending on whether organism true tetraploid or amphidiploid determine how long take population reach hardy–weinberg equilibrium.
complete generalization
for
n
{\displaystyle n}
distinct alleles in
c
{\displaystyle c}
-ploids, genotype frequencies in hardy–weinberg equilibrium given individual terms in multinomial expansion of
(
p
1
+
⋯
+
p
n
)
c
{\displaystyle (p_{1}+\cdots +p_{n})^{c}}
:
(
p
1
+
⋯
+
p
n
)
c
=
∑
k
1
,
…
,
k
n
∈
n
:
k
1
+
⋯
+
k
n
=
c
(
c
k
1
,
…
,
k
n
)
p
1
k
1
⋯
p
n
k
n
{\displaystyle (p_{1}+\cdots +p_{n})^{c}=\sum _{k_{1},\ldots ,k_{n}\ \in \mathbb {n} :k_{1}+\cdots +k_{n}=c}{c \choose k_{1},\ldots ,k_{n}}p_{1}^{k_{1}}\cdots p_{n}^{k_{n}}}
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