5.6

• Biologie
• Middelbare school
• havo, vwo
• Leerjaar 2,3

It runs in the family

5.6 The difference of being a boy or girl

Let's repeat 5.5 first!

What is a mutation?

True or false:
A mutation usually doesn't have an effect in the phenotype

1. True
2. False

Are mutations always negative?

1. yes
2. no

In what type of cells do mutations have the greatest effect on our body?

1. red blood cell
2. egg cell
3. brain cell
4. white blood cell

True or false:
cancer can be the result of a mutation

1. True
2. False

Goals

- Why do certain inherited diseases occur more often in boys than in girls?

- Given a certain combination of parents, how can you determine the genotypes and phenotypes of sex-linked inherited characteristics in the off spring?

One X of two X's

The y chromosome

Could you see all the numbers?

Yes

Nothing

Not all of them

Do you remember?

A recessive allele has to occur twice (on each chromosome) in order to be expressed. If a recessive allele is accompanied by a dominant allele on the other chromosome, the dominant allele will be expressed instead.

Take colour-blindness for example. This characteristic is caused by a recessive allele on the X chromosome. A boy with this allele on his X chromosome is colour-blind. A girl needs not one, but two recessive alleles to be colour-blind.

Color-blindness

X^B stands for normal vision

X^b stands for colour-blindness

The mother is a carrier for colour-blindness: X^B X^b

The father is not colour-blind: X^B Y

Can boys be carriers too for color blindness? Explain why/why not?

It runs in the family

The last royal Russian couple (who lived at the beginning of the 20th century) were Tsar Nicholas Romanov and Tsarina Alexandra, who was a carrier for haemophilia. Although their four daughters, Olga, Tatiana, Maria and Anastasia, did not have haemophilia (some of them may have been carriers), the only son and heir to the throne, little prince Alexei unfortunately did.

Question

What are the chances that one of Alexei his sisters was a carrier of haemophilia? Would Tsar Nicholas and Tsarina Alexandra always produce sons with haemophilia? Why or why not?

What are the chances that one of Alexei’s sisters was a carrier of haemophilia?

1. 0%
2. 25%
3. 50%
4. 100%

Would Tsar Nicholas and Tsarina Alexandra always produce sons with haemophilia?

1. Yes
2. No

5.6

make the assignment

check your answers