Comments

  1. chigau (違う) says

    the GrrlScientist is awesome
    I am sooo creeped out
    everyone go click

  2. knowsu says

    Blue and green should never be seen … without an adequate scientific explanation to support it.

  3. howardhershey says

    I am making an educated guess here, but given the size of avian yolk, fusion chimera after fertilization of a double tolled egg is unlikely. I would argue for mutation at the two-cell stage leading to loss of yellow pigment on the blue side. The chance of that leading to this is higher. I could be wrong. DNA tests of the two sides would be determinative. BTW, because external sex is not determined by hormones in fruit flies, but internally cell by cell, similar flies that are female on one side and male on the other occur because of the loss of an X in one cell at the two cell stage. I presume that pigment distribution is also on a cell level.

  4. Nightjar says

    howardhershey,

    I am making an educated guess here, but given the size of avian yolk, fusion chimera after fertilization of a double tolled egg is unlikely. I would argue for mutation at the two-cell stage leading to loss of yellow pigment on the blue side

    I don’t know in this case, as this bird is obviously male on both sides, but a lot of these half-siders are also male on one side and female on the other (follow the link in the OP for lots of examples).This condition has been investigated in domestic chickens and although the authors’ first hypothesis was mutation or chromosome loss at the two-cell stage, just like you mention, it turned out be wrong:

    Dr Clinton and his colleagues originally hypothesised that one side of bilaterally gynandromorphic birds would be a genetically normal female (or male) while the other side suffered some kind of chromosomal anomaly or mutation. In their journey to understand the molecular and cellular mechanisms that lead to a gynandromorph, these researchers made a fundamental and bizarre discovery about sexual development.

    […]

    Since these data clearly establish the presence of both ZZ- and ZW-containing cells, the team realized that it is highly unlikely that gynandromorphs arise as a consequence of either a mutation or a loss of a sex chromosome at the two-cell stage of development, as they originally predicted. Thus the team proposed that bilateral gynandromorphs start at the very beginning: they result from the failure of the developing ovum to extrude a polar body during meiosis (refer to figure at right). When this abnormal ovum containing two pronuclei is fertilized (by two sperm, a situation known as polyspermy), it contains both a Z- and W-containing nucleus, which then give rise to each half of the whole bird — a bilateral gynandromorph. (Avian sperm only contain the Z sex chromosome, whilst a mature egg cell has either a Z or W sex chromosome.)

  5. howardhershey says

    Again, that can happen in flies because external sex is determined cellularly and not hormonally like mammals. And the Y chromosome does not drive development of external genitalia. Rather it is the ratio of X chromosomes to autosomes. A normal female appearance occurs when the fly has 2 (or more) X: 2 autosome sets. A normal male appearance occurs when the ratio is 1X (regardless of the presence or absence of a Y): 2 autosome sets. Thus the loss of an X at the first division produces a fly with one cell which has a 1X:2A ratio (male) and one cell which is 2 or 3 X: 2A (female).
    In the case of the budgie, I suspect that the green color is the result of the presence of both blue and yellow pigments in the feathers and is determined on an each cell basis. But I haven’t checked to see if that’s the case.

  6. says

    Nightjar @10:

    as this bird is obviously male on both sides

    I ask only because I know nothing about budgies, but how can you tell?

  7. Nightjar says

    NelC,

    I can tell by the colour of the cere (that little nose above the beak). In males it’s blue, in females it’s beige or brown. There are exceptions in some colour variations (such as albino and lutino birds) and it may be harder to tell in those cases, but not in green and blue budgies.

  8. Rich Woods says

    @NelC #12:

    I ask only because I know nothing about budgies, but how can you tell?

    Carefully and respectfully.

    Joking aside, it’s all in the nose. A mature male has a blue nose (the protrusion just above the beak) while a female budgie has one which is pink or brown (I think — I haven’t kept budgies since I was a kid).

  9. moarscienceplz says

    Wow! I never knew chimeras could be so cleanly separate. Grrlscientist shows several examples of bilateral dimorphism, but does that mean that top/bottom dimorphism is impossible?

  10. emergence says

    Oh, I get it. There’s no yellow pigment on that side, so the yellow head turns white and the green body turns blue. It’s funny that I only figured out why some budgies are green and yellow and others are blue and white when I saw this.