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# Protection and Survival ## Overview A child that inherits a tongue-rolling gene from one parent and the non-rolling gene from the other will be able to roll their tongue. This is because the tongue-rolling form of the gene is dominant and takes priority over the non-rolling gene, which is recessi...

# Protection and Survival ## Overview A child that inherits a tongue-rolling gene from one parent and the non-rolling gene from the other will be able to roll their tongue. This is because the tongue-rolling form of the gene is dominant and takes priority over the non-rolling gene, which is recessive. Dominant genes are always expressed (active) preference over recessive genes, requiring only one copy of a dominant gene for expression. A recessive gene can only be expressed if both chromosomes have it, meaning individuals unable to roll their tongues must have two copies of the recessive non-rolling gene. ### Key Concepts - **Homozygous vs Heterozygous**: - Individuals homozygous for a gene have two identical copies (either dominant or recessive). - Heterozygous individuals have one dominant and one recessive gene. ## Punnett Squares - **Figure 17.4**: The probability of inheriting either form of a gene depends on parental make-up. - Example: Punnett square illustrates possible combinations of the tongue-rolling gene in children of heterozygous parents (TT or Tt). - Prediction of the probability that a baby will inherit an inherited disease (e.g., cystic fibrosis) forms the basis of genetic counselling. ### Punnett Square for Tongue-Rolling Gene | Paternal Genes | | | |-----------------------|------|------| | **Maternal Genes** | T | t | | **T** | TT | Tt | | **t** | Tt | tt | - TT: Tongue-roller (Homozygous) - Tt: Tongue-roller (Heterozygous) - tt: Non-tongue-roller (Homozygous) ## Co-Dominance For some traits, there can be more than two alleles that code for it. An example is the inheritance of A and B type antigens on the surface of blood groups. ### Blood Group Inheritance - Possible alleles: A, B, AB, O - An individual may have various combinations of these alleles, affecting blood types. ### Punnett Square for Blood Group Inheritance | Paternal Genes | | | |-----------------------|------|------| | **Maternal Genes** | A | B | | **A** | AA | AB | | **o** | Ao | Bo | - AA: Blood group A - AB: Blood group AB - Ao: Blood group A - Bo: Blood group B ## Sex-Linked Inheritance The Y chromosome is much smaller than the X chromosome, carrying only 200 genes compared to X’s 2000, most of which are involved in sex determination and related traits. ### Reference Figures - **Figure 17.9**: Autosomal inheritance. - **Figure 17.10**: Co-dominant inheritance of ABO blood groups. --- Note: The above information encapsulates genetic inheritance, focusing on tongue-rolling traits and ABO blood groups while highlighting key concepts in genetics.