Sex Linkage • sex linkage is when a given trait is on a sex chromosome • humans: there are few Y-linked traits and several X-linked traits. Y-linked traits affect males only and are always expressed. X-linked traits are always expressed in the male because they only have 1 X chromosome. While females with 1 affected X chromosome are silent carriers for the recessive trait. • birds: there are no known W-linked traits, but there are several Z-linked traits in birds. W-linked traits would affect females only and are always expressed. Z-linked traits are always expressed in the female because they only have 1 Z chromosome. Males with 1 affected Z chromosome are silent carriers for a recessive trait or are affected individuals for a dominant trait. • clues to recognize sex linkage: (1) when reciprocal crosses are done (eg) purple male X pink female and pink male X purple female, they give different results (2) male and female offspring are different (males and females are NOT equally likely to inherit a given trait. (3) males show the trait more often than females.
LUTINO LINEOLATED PARAKEETS
(SEX-LINKED RECESSIVE INHERITANCE)
*Remember that
in birds:
ZZ = MALE
ZW = FEMALE
LEGEND
ZJZJ or ZJW = Green
ZJZj = Split to Lutino (*Are always males because females
only have 1 sex chromosome that can carry the gene therefore they are either
green or lutino)
ZjZj or ZjW = Lutino
(1) ZJZJ (Green) x ZJW(Green) = all Green birds
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ZJ |
W |
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ZJ |
ZJ
ZJ |
ZJ
W |
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ZJ |
ZJ
ZJ |
ZJ W |
(2) ZjZj (lutino) x ZjW(lutino) = All lutino birds
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Zj |
W |
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Zj |
Zj
Zj |
Zj
W |
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Zj |
Zj
Zj |
Zj W |
(3) ZJZj (Split to Lutino) x ZJW (Green) = 25% Green Males, 25% Green Females, 25% Split to Lutino Males, & 25% Lutino Females
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ZJ |
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ZJ W |
Zj |
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(4) ZJZj (Split to Lutino) x ZjW (Lutino) = 25% Split to Lutino Males, 25% Lutino Males, 25% Green Females, & 25% Lutino Females
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ZJ |
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Zj Zj |
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(5) ZJZJ (Green ) x ZjW(Lutino) = 50% Split to Lutino Males & 50% Green Females
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Zj |
W |
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ZJ Zj |
ZJ W |
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ZJ W |
ZJW(Green) x ZjZj (Lutino) = 50% Lutino Females & 50% Split to lutino Males
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W |
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ZJ Zj |
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ZJ Zj |
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(6) Split to Lutino x Split to Lutino =