Ohio Biology EOC B.H (Heredity and Inheritance): meiosis, Mendelian genetics and Punnett squares, inheritance patterns, pedigrees and sex linkage, and biotechnology

What the inheritance topics demand

The Heredity strand (B.H) has a molecular side and an inheritance side. This guide covers the inheritance side: how gametes are made, how traits pass to offspring, the patterns inheritance can take, how to read a family pedigree, and how humans apply genetic knowledge. (The molecular side, with DNA, protein synthesis, and mutations, is in the molecular genetics guide.) The main content statement is B.H.2 (in sexual reproduction, offspring receive genetic information from each parent), with B.H.3 (traits result from genes interacting with the environment) and B.H.5 (DNA determines proteins) feeding the patterns and biotechnology topics. The recurring crosscutting concept is patterns.

This guide ties together the matching topic pages, each with its own practice questions: meiosis and genetic variation, Mendelian genetics and Punnett squares, patterns of inheritance, pedigrees and sex-linked traits, and biotechnology and genetic engineering.

Meiosis and variation

Meiosis makes gametes: one diploid ($2n$) cell produces four haploid ($n$) cells, halving the chromosome number so fertilization restores it. It differs from mitosis by making four genetically different haploid cells instead of two identical diploid ones. Meiosis creates genetic variation through crossing over (homologous chromosomes swap segments), independent assortment (pairs separate randomly), and random fertilization. This variation, together with mutation, is the raw material for evolution. Remember that meiosis shuffles existing alleles; only mutation makes new ones.

Mendelian genetics and Punnett squares

Each parent carries two alleles and passes one to each gamete (segregation). A dominant allele (capital) shows with one copy; a recessive allele (lower case) shows only with two. A Punnett square predicts offspring: put one parent's gametes across the top, the other's down the side, fill the boxes, and count. The classic outcomes are 3:1 phenotypes (and 1:2:1 genotypes) from a $Tt \times Tt$ cross, and 1:1 from a $Tt \times tt$ test cross. Ratios are probabilities over many offspring, so use $3/4$ and $1/4$ for the chance of a single offspring.

Non-Mendelian patterns

Some traits go beyond simple dominance. Incomplete dominance gives a blended heterozygote (red and white make pink). Codominance shows both alleles at once (AB blood type, roan coat). Multiple alleles means a gene has more than two versions in the population (ABO blood type has $I^A$, $I^B$, $i$), though each person carries only two. Polygenic traits are set by many genes and show a continuous range (height, skin color). Match the signature, blend, both-expressed, more-than-two, or continuous, to the pattern.

Pedigrees and sex linkage

A pedigree tracks a trait through a family (circle female, square male, shaded means affected). The key rule: two unaffected parents with an affected child means the trait is recessive (the parents are carriers). Sex is set by the sex chromosomes (XX female, XY male), and the father's gamete decides a child's sex. X-linked recessive traits (color blindness, haemophilia) appear more often in males, because a male's single X means one recessive allele is enough, while a female needs it on both X chromosomes and is more often a carrier.

Biotechnology

Knowing how DNA codes for proteins lets humans apply genetics. Genetic engineering transfers a gene from one organism to another (bacteria given the human insulin gene make insulin), producing a GMO. Selective breeding chooses which organisms reproduce over generations, using existing variation. DNA fingerprinting reads each person's unique DNA pattern to identify individuals or confirm relationships. Each technology has benefits (medicine, food, justice) and concerns (ethics, safety, privacy), and a strong answer names a specific example of each.

Check your knowledge

A mix of recall and reasoning questions covering the inheritance topics. Attempt them under timed conditions, then check against the solutions.

1. A body cell has 20 chromosomes. State the number in a gamete produced by meiosis. (1 mark)
2. Name two processes in meiosis that create genetic variation. (2 marks)
3. Two heterozygous tall plants (Tt) are crossed. State the phenotype and genotype ratios. (2 marks)
4. State the difference between incomplete dominance and codominance. (2 marks)
5. ABO blood type has three alleles in the population. State what this is an example of. (1 mark)
6. In a pedigree, two unaffected parents have an affected child. State whether the trait is dominant or recessive. (1 mark)
7. Explain why X-linked recessive traits are more common in males. (2 marks)
8. State the difference between genetic engineering and selective breeding. (2 marks)