5.6 the difference of being a boy or girl

• Biologie
• Middelbare school
• vwo
• Leerjaar 3

5.6 the difference of being a boy or girl

TB page 141

What is an allele?

What is a dominant allele?

What is a recessive allele?

male and female

male:    2x 22 autosomes + X + Y = 46 chromosomes

female: 2x 22 autosomes + X + X = 46 chromosomes

egg cell and sperm cell

egg cell contains 22 autosomes + X chromsome

sperm cell contains 22 autosomes + X or 22 autosomes + Y

today''s program 

learning objectives: you're able to answer the following questions

• why do certain inherited diseases occur more often in boys than in girls?


• given a certain combination of parents, how can you determine the genotype and phenotype of sex-linked inherited characteristics in the offspring? 

Sex-linked inheritance

• Female: XX,  male: XY
• Traits are only on the X chromosome
• On the Y are only the genes for male-ness
• Genotypes are written down like this (when they are sex linked!) :
  Female: X^HX^H, X^HX^h or X^hX^h 

     Male: X^HY or X^hY 

calculating chances

1. Write down both genotypes XX and XY
    with the trait X^HX^H and X^hY for example

2. Use a punnet square!

3. Calculate the chance of every possible phenotype and       
    answer the question

LET'S PRACTISE TOGETHER

A mother who is a carrier for colour-blindness gets a child with a father who has normal vision. 

What are the probabilities of their children being colour-blind? Use a Punnet square! 

colour-blindness is sex-linked!

question 41

start homework!

study 5.6

do excercise 41, 42, 43, 44, 45