Inheritance in action

1. I can explain how sex (gender) is determined in humans. Inheritance in action I can predict what features a child might inherit.

2. 46…or 23 homologous pairs How many chromosomes do humans have? 23 from Mom and 23 from Dad How many chromosomes determined whether you were a boy or a girl?

3. Its all down to Dad…. The Sex chromosomes If you get a Y you’re a boy.

4. Its all down to Dad…. The Sex chromosomes If you get an X you’re a girl.

5. Prof. Reginald CrundallPunnett 1875-1967 Punnett Squares X X X XX XX XY Y XY

6. How is your gender decided by chromosomes? Questions Twins are born. Twin A is XY and twin B is XX. What sex are the two babies?

7. Tongue rolling Dangly earlobes Eye colour Cleft Chin Hair colour What other characteristics could we predict for? Dimples A characteristic is controlled by the two forms of a gene present in an individual. These are called alleles.

8. Could we calculate a probability on what we would expect to see? Yes But to understand this we need to add some new words to our glossary.

9. Phenotype Genotype physical appearance of an organism. the set of genes (alleles) that an organism possesses Homozygous Heterozygous when two alleles (gene types) are identical when the two alleles are different Allele different forms of the same gene

10. Dominant allele which controls the characteristic whenever it is present. BB or Bb recessive allele whose characteristics only show up when it is present on both chromosomes bb

11. The allele for dimples (D) is dominant over the allele for no-dimples (d). Dimples D D Probability of a child with dimples 100% d Dd Dd Dd d Dd

12. The allele for dimples (D) is dominant over the allele for no-dimples (d). Dimples d d Probability of a child with dimples 0% d dd dd dd d dd

13. The allele for dimples (D) is dominant over the allele for no-dimples (d). Dimples D d Probability of a child with dimples 75% D DD Dd Dd d dd

14. The allele for dimples (D) is dominant over the allele for no-dimples (d). Dimples D d Probability of a child with dimples 50% d Dd dd Dd d dd

15. The allele for normal melanin (M) is dominant over the allele for albinism (m). Albinism m M Probability of a child with albinism 25% M MM Mm mm Mm m

16. The allele for wet earwax (W) is dominant over the allele for dry earwax (w). Earwax W W Probability of a child with dry earwax 0% w Ww Ww Ww Ww w

17. The allele for six fingers (P) is dominant over the allele for five fingers (p). Polydactyly p P Probability of a child with six fingers 50% pp p Pp pp Pp p

18. 1. What is a dominant allele? 2. What is a recessive allele? Questions 3. What does homozygous and heterozygous mean? 4. If a heterozygous man with dimples fathers a child with a woman with no dimples what is the probability of a child with dimples?

19. Using the Internet: • Look for further examples of inherited characteristics (in man and other species). • Contrast how pattern of inheritance is effected when linked to sex chromosome. • Investigate arguments why many classic Mendelian traits have been discredited and are now thought to be much more complicated. Stretch your mind…