Flashcards · Biology · Genetic Inheritance
Sex Determination
-
How many pairs of chromosomes are in a human body cell?
23.
-
How many pairs control characteristics only?
22.
-
What does the 23rd pair carry?
The genes that determine sex.
-
What are the sex chromosomes of a female?
XX.
-
What are the sex chromosomes of a male?
XY.
-
Which chromosome is shorter, X or Y?
Y.
-
Which sex chromosomes do eggs carry?
Every egg carries an X.
-
Which sex chromosomes do sperm carry?
Half carry X and half carry Y.
-
What is the sex of a baby if a Y sperm fertilises the egg?
A boy (XY).
-
What is the sex of a baby if an X sperm fertilises the egg?
A girl (XX).
-
What is the ratio of girls to boys from a genetic cross?
1 : 1.
-
What is the chance that a baby is a girl?
50%, or 1 in 2.
-
A couple have four girls. What is the chance that the next baby is a boy?
50%, because each birth is independent.
-
Who decides the sex of the baby, the mother or the father?
The father, because his sperm carries either X or Y.
-
Why is the 1 : 1 ratio only seen in large populations?
Each fertilisation is a chance event, so small families vary.
-
Draw and complete a Punnett square to show sex inheritance in humans and give the ratio.
The mother is XX and makes X eggs. The father is XY and makes X and Y sperm. The squares are XX, XY, XX and XY, so the ratio of girls to boys is 1 : 1.