Gender Determination in Humans

BC Science Probe 9Section 4.4

Pages 123-126

The Human Karyotype

• The arrangement of an organism’s chromosomes from one body cell is called a karyotype.

The Human Karyotype

• Scientists construct karyotypes by taking pictures of condensed chromosomes during metaphase, then cutting them out and arranging them.

The Human Karyotype

• This human karyotype has 23 pairs or 46 chromosomes.

Sex Chromosomes

• There is one pair of chromosomes that determine the gender of the individual.

• These are called sex chromosomes.

Sex Chromosomes

• Both the primary and secondary sex characteristics are controlled by the 2 sex chromosomes.

Sex Chromosomes

• The 2 sex chromosomes are the X and the Y.– The X is the larger one.– The Y is the smaller one.

Sex Chromosomes

• Females have 2 X chromosomes.• Males have 1 X and 1 Y chromosome.

Sex Chromosomes

• The gametes that are produced during meiosis each get one sex chromosome from the parent.– All of the female’s eggs will have X’s– ½ of the male’s sperm will have X’s, the other ½

will have Y’s.

Male Zygotes or Female Zygotes

• Male or female all depends on which sperm fertilizes the egg.

• Since all the eggs have a single X chromosome, it depends on whether it’s a sperm cell with an X or a Y that fertilizes it.

Male Zygotes of Female Zygotes

Male Zygotes or Female Zygotes

• ½ the sperm produce male offspring • ½ produce female offspring• This means that there is a 50% chance that the

child will be male and a 50% chance that the child will be female.

• Gender is determined by the father.

Sex-linked Characteristics

• There are some traits that are more common in men than in women.

• This is because the X and Y chromosomes are not homologous (they do not carry matching genes).

Sex-linked Characteristics

• Females get 23 pairs of homologs because of the 2 X’s.

• The smaller Y that the males get are missing some information.

Sex-linked Characteristics

• Certain traits are controlled by the genes on the X-chromosome.

• These are known as sex-linked characteristics.• They occur more frequently in males than in

females.

Sex-linked Characteristics

• Examples:– Red-green colour blindness

Sex-linked Characteristics

• Examples:– baldness

Sex-linked Characteristics

• Examples:– hemophilia