IB Sex determination © Oxford University Press 2011 Sex determination

IB Sex determination © Oxford University Press 2011 We can use a genetic diagram to show how sex (gender) can be determined. The diagram shows how there is an equal chance that each baby will be a girl or a boy. Click to advance the diagram.

IB Sex determination © Oxford University Press 2011 We can use a genetic diagram to show how sex (gender) can be determined. The diagram shows how there is an equal chance that each baby will be a girl or a boy. Click to advance the diagram.

IB Sex determination © Oxford University Press 2011 We can use a genetic diagram to show how sex (gender) can be determined. The diagram shows how there is an equal chance that each baby will be a girl or a boy. Click to advance the diagram.

IB Sex determination © Oxford University Press 2011 We can use a genetic diagram to show how sex (gender) can be determined. The diagram shows how there is an equal chance that each baby will be a girl or a boy. Click to advance the diagram.

IB Sex determination © Oxford University Press 2011 We can use a genetic diagram to show how sex (gender) can be determined. The diagram shows how there is an equal chance that each baby will be a girl or a boy. Click to advance the diagram.

IB Sex determination © Oxford University Press 2011 You should note that:  Half the male gametes (sperm) have an X chromosome and half have a Y chromosome.  However, all the female gametes (eggs) have an X chromosome.  Fertilization is random and either type of sperm could fertilize an egg.  At each pregnancy, there is a 50:50 chance of conceiving a girl or a boy.  In a large population, there will be equal numbers of male and female offspring.

IB Sex determination © Oxford University Press 2011 When constructing a genetic diagram for a monohybrid cross, it is important to follow these conventions:  Show the characteristic of the parents (phenotype).  Show the alleles present in the parents’ cells (genotypes).  Use upper case letters to represent a dominant allele.  Use the lower case version of the same letter to show a recessive allele.  Put gametes in circles.  Show all the different possible combinations of alleles at fertilization.  Put an ‘x’ to show a cross (mating).

IB Sex determination © Oxford University Press 2011 Below is an example of how you might construct a genetic diagram to explain a monohybrid cross between a father who has two alleles for free earlobes and a mother who has two alleles for attached earlobes. Which conventions of drawing genetic diagrams do you recognize? Offsprings’ characteristics: all have free earlobes but have one dominant and one recessive allele

IB Sex determination © Oxford University Press 2011 Below is an example of how to write the last genetic diagram as a punnet square. Ee

IB Sex determination © Oxford University Press 2011 Now have a go at your own punnet squares 1.A Blue eyed mum (bb) crossed with a Brown eyed father (BB) 2.A Tortoise shell cat (TT) crossed with a Ginger hair cat (tt) 3.A brown eyed mum (Bb) crossed with a Brown eyed father (Bb) 4.A Red flowered pea plant (Rr) crossed with a Yellow pea plant (rr) 5.A Wrinkled pea (WW) With a Smooth pea (ww)