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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. - PowerPoint PPT Presentation
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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