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Thread: This weeks question on genitics. (Senior Scientific)

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    Senior Member Greengage's Avatar
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    Default This weeks question on genitics. (Senior Scientific)

    I am just no god at these questions. (b)Assume that bees have just two eye colours, yellow denoted by Y and brown denoted by y. If 30% of the drones that mate with a heterozygous yellow eyed queen are brown eyed drones determine the percent of each genotype and phenotype of their offspring. (14 marks)

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    Devil is the detail....to me their is ambiguity in whether they are simply asking for the off spring of the 30% drones (y) (inferred by asking for details of their progeny) or the whole 100% that the queen mated with...which would be unfair as they don't give any details of the remaining 70% of the drones, although you could infer that they were Y (yellow) as only other thing they could be.
    So for 10 offspring with the first 3 drones (30%) y mated with queen Yy.
    1. Yy
    2. yy
    3. 50% chance of Yy or yy for the third offspring....so need to do a twenty offspring.

    However you look at it this comes out at 50%Yy and 50%yy

    Assuming other drones are Y x Yy queen
    4. YY
    5.YY
    6.YY
    7 Yy
    8. Yy
    9.Yy
    10 50% Chance of being Yy or YY

    and if you work out the phenotype I make it 80% are yellow eyed.

    Hope that is of some small help and not too confusing.
    Last edited by Thymallus; 01-02-2018 at 09:56 AM.

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    Senior Member Greengage's Avatar
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    I had to do a bit of work and figure out the meaning of terms.
    Genes account for variation in inherited characteristics.
    Allele are an alternative form of the same gene where a number of different types of the same gene exist.
    Homozygous: Both Alleles are the same.
    Heterozygous: Two alleles are different.
    Gamete: is a haploid sex cell.
    Dominance: One Allele masks the effects of the other allele.
    Recessive: The Alleles effect is only expressed when both Alleles are the same. (Homozygous)
    Haploid: is a term used when a cell has half the number of chromosomes.(Drones)
    Diploid: is a term used to describes a cell with two sets of chromosomes. (Workers and Queen)
    Genotype: Genetic make up of an individual.
    Phenotype: physical make up of an individual.

    Alleles/ Homozygous/ Heterozygous/Dominance/ Recessive.
    There can be a number of different Alleles controlling the same characteristics such as eye colour in humans Blue, Green and Brown.

    Here we are looking at honey bee eyes.
    Each Insect Drone/Queen has a maximum of two alleles for each characteristic for example a bee with black eyes could have two black eye alleles or one black eye allele and one white eye allele.
    Alleles are usually assigned letters with a capital letter signifying a dominant Allele and a lower case letter signifying a recessive Allele. B (Dominant)Brown eyes b (Recessive) White eyes.
    BB is described as Homozygous dominant.
    Bb is described as Heterozygous.
    bb is described a Homozygous recessive.

    A genetic cross is a table showing how characteristics are inherited.

    Then I wrote out the question again as I thought it a bit of tongue twister.

    (b) Assume that bees have just two eye colours, yellow denoted by Y and brown denoted by y. If 30% of the drones that mate with a heterozygous yellow eyed queen are brown eyed drones determine the percent of each genotype and phenotype of their offspring. (14 marks)

    Assume that bees have just two eye colours, yellow denoted by Y (Dominant)and brown denoted by y (Recessive). If 30% of the drones that mate with a heterozygous (Both Alleles the same) yellow eyed queen are brown eyed drones determine the percent of each genotype (genetic make up of individuals)and phenotype ( physical make up of individuals) of their offspring. (14 marks)

    I cannot disagree with your answer as I don't know enough but will have a go when I get my head around it. Thanks for looking at it.
    Last edited by Greengage; 01-02-2018 at 02:27 PM.

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    Senior Member Mellifera Crofter's Avatar
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    Can one have a heterozygous yellow-eyed queen? I thought yellow is recessive - so, if she is heterozygous, she must be Yy - and that is brown.
    Or am I making a fool of myself now?
    Kitta

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    Quote Originally Posted by Mellifera Crofter View Post
    she must be Yy - and that is brown.
    Usual nomenclature is that capital letters represent the dominant allele and the question states capital Y is yellow, meaning Yy will be be Yellow. Drones only have one allele (as haploid) so if brown they are all lower case y.
    It's very badly phrased question...shoot the examiner.

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    Quote Originally Posted by Greengage View Post
    I am just no god at these questions. (b)Assume that bees have just two eye colours, yellow denoted by Y and brown denoted by y. If 30% of the drones that mate with a heterozygous yellow eyed queen are brown eyed drones determine the percent of each genotype and phenotype of their offspring. (14 marks)
    The question is clear! 30% of all of the drones that mate with the queen.
    Always, (genetics convention dictates) a capital Y means it is the dominant allele: and conversely, a lower case letter - ie y means the recessive allele. (This might not be the case in real life, but if you are trying to work out the genetics question you have to go with the information they give you!)

    So - a heterozygous yellow-eyed queen has a genotype Yy. She mates with 30% brown-eyed drones, whose genotypes are y and 70% of the drones are yellow-eyed and their genotype is Y.
    The queen produces eggs - half are Y and half are y.

    You can work out which eggs are fertilised by the sperm from the two different drones. This is best done by producing a table :
    Queen eggs  Y y
    drones 3y 3Yy 3yy
    7Y 7YY 7Yy (Sorry table doesn't come out too well!)

    Take the queen eggs with Y in the second-from-right column – they can be fertilised by 3y sperm to give 3Yy females. And they can be fertilised by 7Y sperm to give 7YY females.
    Take the queen eggs with y in the last column – they can be fertilised by 3y sperm to give 3yy females. And they can be fertilised by 7Y sperm to give 7Yy females.
    Taking the numbers from the table and the genotypes –
    7YY : 10Yy : 3yy
    For every 20 fertilised eggs (7/20) x 100 = 35% are YY
    (10/20) x 100 = 50% are Yy
    (3/20) x 100 = 15% are yy
    Phenotype refers to how the characteristic appears – yellow- or brown-eyed.
    Only yy are brown-eyed, so that’s 15%.
    YY and Yy are yellow-eyed, so that is all the rest, 35 + 50, ie 85%.
    Hope that helps.

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    Senior Member Mellifera Crofter's Avatar
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    Quote Originally Posted by Thymallus View Post
    Usual nomenclature is that capital letters represent the dominant allele and the question states capital Y is yellow, meaning Yy will be be Yellow. Drones only have one allele (as haploid) so if brown they are all lower case y.
    It's very badly phrased question...shoot the examiner.
    Yes, shoot the examiner. I understand the convention that the uppercase letter is dominant - but in this case it is wrong. Yellow is recessive, so yellow cannot be capital Y, and she can't be Yy. As I understood it, Dzierzen used Italian bees to prove parthenogenesis precisely because yellow is recessive (using cordovans). Or are there cases where yellow isn't recessive?
    Kitta

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    Senior Member Greengage's Avatar
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    Thanks for the interest in this topic.

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    Senior Member Mellifera Crofter's Avatar
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    Ps: anyway, if I pretend the queen is yellow-bodied rather than yellow-eyed, I agree with Jane’s answer.

    But that might be wrong too. I think yellow-bodied is also recessive, which is why C4U told us imported bees soon revert to dark bees).


    Sent from my iPhone using Tapatalk

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    Quote Originally Posted by Mellifera Crofter View Post
    Yes, shoot the examiner. I understand the convention that the uppercase letter is dominant - but in this case it is wrong. Yellow is recessive, so yellow cannot be capital Y, and she can't be Yy. As I
    Kitta, you are right about yellow being recessive in reality....but in the fictitious world of the question it states a heterozygous yellow eyed queen, so for the sake of the question Y (yellow) must be dominant.

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