What is meant by the term X-bearing sperm?
Reveal answer
Sperm containing an X chromosome.
Key words: X-bearing sperm
4(b) INHERITANCE · RECALL
4.27 Sex determination
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What is meant by the term Y-bearing sperm?
Reveal answer
Sperm containing a Y chromosome.
Key words: Y-bearing sperm
What is meant by the term sex determination?
Reveal answer
Biological processes establishing pathways of sexual development.
Key words: sex determination
What is meant by the term random fertilisation?
Reveal answer
Fusion in which any compatible gamete may combine by chance.
Key words: random fertilisation
Sex-chromosome cross: for X egg + X sperm, give the zygote and the common developmental association.
Reveal answer
Zygote: XX. Common developmental association: Typically female.
Key words: X egg + X sperm
Sex-chromosome cross: for X egg + Y sperm, give the zygote and the common developmental association.
Reveal answer
Zygote: XY. Common developmental association: Typically male.
Key words: X egg + Y sperm
Sex-chromosome cross: for Probability per conception, give the zygote and the common developmental association.
Reveal answer
Zygote: About 1/2 each. Common developmental association: Independent event.
Key words: Probability per conception
Sex-chromosome cross: for Source of difference, give the zygote and the common developmental association.
Reveal answer
Zygote: Sperm X or Y. Common developmental association: Paternal gamete contribution.
Key words: Source of difference
True or false, and why? “The egg determines whether a zygote is XX or XY.”
Reveal answer
False. Eggs normally carry X; sperm contribute X or Y.
True or false, and why? “After several sons, a daughter becomes due.”
Reveal answer
False. Each conception is an independent event.
True or false, and why? “A parent can control the chromosome carried by the fertilising sperm through ordinary behaviour.”
Reveal answer
False. Fertilisation is probabilistic and not a matter of blame or choice.
What is the probability that a baby will be genetically female (XX)?
Reveal answer
0.5 (50%, 1 in 2).
Key words: 0.5
Why is the chance of XX or XY about 50 : 50?
Reveal answer
Half of sperm carry X and half carry Y; every egg carries X.
Key words: X · Y
Which parent’s gamete decides whether a zygote is XX or XY?
Reveal answer
The father’s (the sperm).
Key words: father
Which sex chromosome does every human egg carry?
Reveal answer
X.
Key words: X