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Sci9q1m2 sex chromosome and sex determination


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Sci9q1m2 sex chromosome and sex determination

  1. 1. Sex Chromosome and Sex Determination
  2. 2. How many chromosomes do humans have? 46 Chromosomes How many pairs of chromosomes do each individual have? 23 pairs of chromosomes for both males and females What do you call the 22 pairs of chromosomes? Somatic chromosomes How about the 23rd chromosome? Sex chromosome
  3. 3. •Human males and other male organisms, such as other mammals and fruit lies, have non identical sex chromosomes (XY). •Females have identical (XX) sex chromosomes.
  4. 4. How is sex determined and inherited?
  5. 5. Figure 3. Gamete formation involving only sex chromosomes Sex chromosomes Meiosis Gametes
  6. 6. Figure 4: Sex determination
  7. 7. If an egg is fertilized by a sperm with a Y chromosome, as shown in Figure 4, the offspring is male. When an egg is fertilized by a sperm carrying an X chromosome, the offspring is female. Note that there is a 50 percent chance of having a male or female offspring. The greater the number of offspring, the greater is the chance of getting the expected 1:1 ratio of male and female.
  8. 8. Activity 4: Girl or Boy ? Objective: Discuss how sex in humans is determined Materials: Activity sheets Pen paper
  9. 9. Procedure: 1. Draw a Punnett square which shows the inheritance of the sex chromosomes. Represent the female sex chromosomes with XX and the male sex chromosomes with XY.
  10. 10. Guide Questions: Q 13. What will be the sex of a child produced when an egg is fertilized by a sperm that has a Y chromosome? _________________________ Q 14. What type of sperm must fertilize an egg to result in a female child?____________________ Q 15. Based on this Punnett Square, what percent of children would you expect to be male?___________________
  11. 11. Q 16. Which sex chromosome is present in both male and female?__________________________ Q 17. Infer which sex chromosomes determines a person’s sex._________________________ 18. What are the other factors that may influence the expression of human sexuality?._________________
  12. 12. Answers:Q 13. Male Q 14. X bearing sperm Q15. 50% Q16. X chromosome Q17. Y chromosome Q18. Environmental factors, such as age of mother that may lead to nondisjunction (Trisomy 21), Aneuploidy where there is an excess or lack of X or Y chromosome and genital development during conception, and the social interactions after birth may contribute to a certain degree to the expression of human sexuality.
  13. 13. Key Concepts •Males have 44 body chromosomes and two sex chromosomes X and Y. The males determine the sex of their children. •Females have 44 body chromosomes and two sex chromosomes, both X. The total number in each cell of an individual is 46. These chromosomes contain the genes, which are the factors of heredity.