The bicoid gene is a coordinate maternal–effect gene. If loss ...

Question

The bicoid gene is a coordinate maternal-effect gene.

A female Drosophila heterozygous for a loss-of-function bicoid allele is mated to a male that is heterozygous for the same allele. What are the phenotypes of their progeny?

Accepted Answer

Welcome back, everyone. Let's look at our next question. It says, what is the phenotype of an individual that is homozygous for B coid loss of function. All choice, a normal embryonic development for males and abnormal anterior posture axis formation and the embryos derived from the eggs of such females for females. Choice B abnormal development for males or lethality for females. Choice c abnormal anterior posture ais formation for females or enhanced growth for males or choice d increased fertility compared to normal females for females or abnormal fertility for males. Well, let's think through what would be the result of a loss of function mutation to both bi coid gene allies. So our individuals have non functioning hm quaid gene two copies. So they have no functioning bio gene whatsoever in the individual. Well, why do our answer choices leave us options for males or females? Because by coid, we recall from our content video is a maternal effect gene which means it's active in the egg. And when the zygote begins to develop, it gets its bi coid distribution from the original egg cell. So directly and solely from the mother. So the bio or genotype excuse me of the individual does not affect the development of that individual. So, bio genotype of the individual does not affect the embryonic development of that particular individual. What matters is the bio genotype of the mother because that will be establishing the bi cod distribution in the zygote. So, bio distribution in the egg establishes bi coid distribution in the zygote and then affecting the embryonic development. So that's the key thing to keep in mind here. So in that case, when we think about males, again, they're getting their bi coid from their mother as a maternal effect gene. So if the male himself doesn't have any functioning bio, that won't have any effect on him. So we'd expect to see normal embryonic development from males. So we see that in choice, a normal embryonic development for males, we can eliminate choice B which is abnormal development for males because that won't be in effect. And then choice C says enhanced growth for males, but we can eliminate that. It's not going to cause any enhanced growth. And then a choice D says abnormal fertility for males. Well, it wouldn't affect their fertility because again, by coid comes from the mother, the bi coid is in the egg cell and so it won't have any effect on the fertility of the males. So we're just going to eliminate that. Well, now by process of elimination, we just have choice a left. But for purposes of understanding, let's keep on going and really thoroughly evaluate this. Then the rest of choice says abnormal anterior posture axis formation in the embryos derived from the eggs of such females. Well, that is correct. It won't affect the development of the females themselves because they get their bi coid from their mothers. But the eggs that develop in their body will then be lacking functional bio bio does determine anterior posture axis formation. So any eggs, this fe these females generate will not be able to develop that anterior posture axis. And therefore it will affect embryos, derive from those females, not the females themselves. So choice A is correct. Um We'll just evaluate B through D, we've already eliminated them, we know they're not correct. But again, in the interest of full understanding, let's look at what it says for females to understand why these pro choices are not correct. So in choice B it says lethality for females. Again, those females won't have any effects on themselves. Just the next generation. Joyce says abnormal Antero posture axis formation for females that one might look correct on first glance. But again, it won't affect the axis formation of the individual with the mutation. They get their bird from their mother. It will affect the axis formation in their eggs and therefore their embryos. And then choice D has increased fertility compared to normal females. Well, no, you would not expect that. So again, our correct answer for the phenotype of an individual that is homozygous for bi coid loss of function. All is choice a normal embryonic development for males, abnormal anterior posture axis formation and the embryos derived from the eggs of such females. See you in the next video.

The bicoid gene is a coordinate maternal–effect gene. If loss of bicoid function in the egg leads to lethality during embryogenesis, how are females homozygous for bicoid produced? What is the phenotype of a male homozygous for bicoid loss-of-function alleles?

Key Concepts

Maternal Effect Genes

Homozygosity and Lethality

Phenotype of Loss-of-Function Alleles

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