SEX CHROMOSOMES What are sex chromosomes? Why are sex chromosomes important in the study of inheritance of gender? Explain the term inheritance of gender. Explain why a human baby’s gender is determined by the sperm that fertilises the egg cell. Copy right Science-Tutors 2008 www.sciencetutors.zoomshare.com Compilation By Ivan Ukiwah

Sex Chromosomes And Gender Determination Contents of Power point Sex Chromosomes What I Need to know Genetic or Environmental Variation (1 and 2) Continuous and Discontinuous Variation Quick Quiz Clones (Identical Twins) Copy right Science-Tutors 2008 www.sciencetutors.zoomshare.com Compilation By Ivan Ukiwah

WHAT I NEED TO KNOW A human baby’s gender is determined by the sperm that fertilises the egg cell. The male Y chromosome carries a gene called the 'sex-determining region Y’ also know as SRY. Genetic information are passed from parents to offspring's in their sex cell Sex cells are egg cells and sperm cells When egg cells and sperm cells join together in fertilisation the contain full 23 pairs of chromosomes. One pair of chromosome (23) comes from the mother and the other pair (23) comes from the father. Copy right Science-Tutors 2008 www.sciencetutors.zoomshare.com Compilation By Ivan Ukiwah

GENETIC OR ENVIRONMENTAL VARIATION? Mark and John are identical twins and are genetically the same. Mark takes regular exercise and have better muscle tone than John who does not. However there are some differences between John and Mark - for example, in personality, fashion tastes or dress sense, intelligence, relationships, likeability factor, confidence, and aptitude Underline environmental variation using red pen or pencil Which of these differences are due to their a) experiences or environment b) genes. Copy right Science-Tutors 2008 www.sciencetutors.zoomshare.com Compilation By Ivan Ukiwah

CONTINUOUS AND DISCONTINUOUS VARIATION Think back to some of the difference between people in your class Explain the meaning of the following: Continuous Variation Discontinuous Variation Write down six examples continuous variation Write down three examples of discontinuous variation.

CONTINUOUS AND DISCONTINUOUS VARIATION A variation with a progressive range of values which change gradually is called CONTINUOUS VARIATION. A variation in which there is not a continuous range of options is called a DISCONTINUOUS VARIATION.

QUICK QUIZ Which of these graph represents a continuous and a discontinuous variation and explain why? No. of Pupils No. of Pupils in 10f1/SC Attached Ears Detached Ears 10FI/SC Height of students (cm) Say whether each variation is a continuous or discontinuous: Natural eye colour, a scar, tongue rolling, attached ear lobes, free or detached ear lobes, height, hair length.

Distribution Pattern in Variation Height is affected by several genes, so more complicated than being either tall or short. Also affected by the environment.

HUMAN CLONES Explain why identical twins are clones of each other but not of their parents. Ask students if there will be variation between offspring. Draw out that variation between clones has environmental cause. Define CLONING