Gender Determination in Humans BC Science Probe 9 Section 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 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