Genetics and Inheritance

1. Part 3: Predicting Possibilities Genetics and Inheritance Year 10 Biology

2. 2. Genes are passed on from one generation to the next! Your Genotype & Phenotype make youwho you are!

3. 3. Genes are passed on from one generation to the next! Predicting possibilities • A Punnett square is a diagram that is used to predict the outcome of a genetic cross. Shows which alleles for a particular trait are present in the gametes of each parent. Shows possible ways in which these alleles can be combined.

4. 4. Genes are passed on from one generation to the next! Punnett square rules The alleles in each of the parent’s genotypes for that trait are put in the outside squares and then multiplied together to show the possible genotypes of the offspring. Inheritance is complete dominance: capital letter for the allele of the dominant trait (e.g. B) and a lower-case version of the same letter for the allele for the If the type of inheritance is incomplete or codominant, then different letters are used to represent them (e.g. R and W or IAandIB ). The sex chromosomes are included when an X-linked trait is involved (e.g. XB Xb and XB Y).

5. 5. Genes are passed on from one generation to the next! Complete Dominance

6. 6. Genes are passed on from one generation to the next! Complete Dominance

7. 7. Genes are passed on from one generation to the next! Punnett Square • Punnett squares show us the chance of offspring inheriting particular combinations

8. 8. Genes are passed on from one generation to the next! Pedigree Charts A diagram that shows a family’s relationships and how characteristics are passed on from one generation to the next is a pedigree chart.

9. 9. Genes are passed on from one generation to the next!

10. 10. Genes are passed on from one generation to the next! Use the diagram to draw a pedigree chart

11. 11. Genes are passed on from one generation to the next! What is your blood type? • Three different alleles for the ABO gene. • Two carry instructions to make a particular type of protein called an antigen; the other does not. • One allele codes for antigen A and the other codes for antigen B. • If you possess both of these alleles, then you have the instructions to produce both antigen A and antigen B. • This is an example of co-dominant inheritance because both blood types are expressed in the heterozygote. The inheritance of blood types A, B, AB and O are determined by the ABO gene.

12. 12. Genes are passed on from one generation to the next! What is your blood type? • Co-dominance • Heterozygote has the characteristics of both parents • (e.g. human blood groups)

13. 13. Genes are passed on from one generation to the next! Calculating Co-dominant Inheritance • Refer to the ABO gene as I,the allele that codes for antigen A could be referred to as IA. • Antigen B could be referred to as IB. • Neither antigen could be referred to as I, • The ability to make antigen A or B is shown as a capital letter because it is dominant. • The inability to make either antigen is recessive and shown as a lowercase letter.

14. Calculating Co-dominant Inheritance 14. Genes are passed on from one generation to the next!

15. 15. Genes are passed on from one generation to the next! Can you have a different blood type to your parents? Discuss the question with a person nearby

16. 16. Genes are passed on from one generation to the next! Chromosomes can be Autosomes or Sex Chromosomes • Males have XY • Females have XX Somatic cells have 23 pairs of chromosomes, numbered 1-23 depending of size. 22 pairs of autosomes 1 pair of sex chromosomes

17. 17. Genes are passed on from one generation to the next! Inheritance • The passing of characteristics from one generation to the next • Inheritance can be: • Autosomal inheritance (Chromosomes that are not X or Y) Inheritance of traits where genes are located on autosomes • Sex-linked inheritance (Chromosomes that are X or Y) Inheritance of traits where genes are located on sex chromosomes • X-Linked Inheritance (On X Chromosome) • Y-Linked inheritance (On Y Chromosome) • Most examples of Sex linked inheritance (Sex-linkage) are X-linkage, since the Y chromosome is small and does not contain many genes.

18. 18. Genes are passed on from one generation to the next! Sex-linked inheritance • Males, who possess only one X chromosome, are hemizygous and would have the genotypes XBY or XbY. When stating the phenotypes for X-linked traits it is important to also specify the person’s gender (e.g. colour blind male). • Examples of X-linked recessive traits are: • Haemophilia • some forms of Colourblindness • Females need to receive two alleles for the recessive trait, males need to receive only one. • There is a greater chance of males showing these traits than females. • Genotype for X-linked traits • Heterozygous, XBXb • Homozygous, XbXb or XBXB.

19. 19. Genes are passed on from one generation to the next! Can males be homozygous for an X-linked trait? Discuss the question with a person nearby

20. 20. Genes are passed on from one generation to the next! X-Linked Inheritance

21. 21. Genes are passed on from one generation to the next! Variation in a family! In each family there are similarities and also differences! Traits can “skip” a generation if parents are carriers of a recessive allele. There are 8 388 608 possible chromosome combinations when forming gametes during Meiosis! Crossing over can occur between chromosomes, one chromosome swaps its genetic information with another.