The Role of Chromosomes

• Chromosomes are made from DNA and carry information in the form of genes which determines the characteristics of living things. There are 23 pairs of chromosomes in the body and the 23rd pair determines biological sex
• The chromosomal structure for females is XX and XY for males. Normal egg cells have an X chromosome, whilst sperm cells carry a X or Y chromosome
• The baby will be a boy if the fertilising sperm carries a Y chromosome and a girl if it carries a X chromosome. The Y chromosome carries a genes called the sex determining region Y. This causes the testes to develop and produce androgens causing the embryo to become a male
• Gender development occurs through the influence of hormones. Hormones cause the development of reproductive organ in the womb and during puberty hormonal activity triggers the development of secondary characteristics. Males and female produce similar hormones but in different concentrations
• Testosterone is the male hormone and small quantities can be present in women. It controls the development of male sex hormones during foetal development
• The evolutionary explanation for testosterone states that high levels of testosterone are linked to aggression because it’s adaptive. Aggression towards rivals allows males to compete for the opportunity to mate with a fertile female
• Oestrogen is a female hormone that determines female sexual characteristics and menstruation. Oestrogen causes women to experience heightened emotionality and irritability during their menstrual cycle. This is known as premenstrual tension (PMT) when the effects become a diagnosable disorder
• Oxytocin in is produced in larger amounts in women compared to men, as a result of giving birth. The hormone stimulates lactation so mothers can breast feed their child and it reduces the release of cortisol, which makes the mother in love with their baby