Sign up to access the complete lesson and track your progress!
Unlock This CourseGenetics is like a secret code that determines everything about living things - from your eye colour to whether you can roll your tongue! Understanding genetic terminology is essential for decoding how traits pass from parents to offspring. Think of it as learning the language of inheritance.
Every living thing carries genetic information in their cells and this information follows specific rules and patterns. By mastering the key terms, you'll be able to predict what offspring might look like and understand why family members share similar characteristics.
Key Definitions:
Think of genes as recipe books and alleles as different versions of the same recipe. For example, the gene for eye colour has different alleles - one for brown eyes, one for blue eyes, one for green eyes. You inherit one allele from each parent, giving you two alleles for each gene.
Not all alleles are equal! Some are bossy (dominant) while others are quiet (recessive). Understanding this relationship is crucial for predicting inheritance patterns.
Dominant alleles are represented by capital letters (like B for brown eyes) and always show up in the phenotype when present. Recessive alleles use lowercase letters (like b for blue eyes) and only show up when there are two copies present.
Always expressed when present. Only need one copy to show the trait. Examples: Brown eyes (B), Dark hair (D), Ability to roll tongue (R).
Only expressed when two copies are present. Hidden when paired with dominant alleles. Examples: Blue eyes (b), Light hair (d), Cannot roll tongue (r).
Both alleles are equally dominant and both show up. Example: AB blood type where both A and B alleles are expressed together.
Sarah has brown eyes (BB) and marries Tom who has blue eyes (bb). All their children will have brown eyes (Bb) because brown is dominant over blue. However, these children carry the recessive blue allele, so their children might have blue eyes if they inherit two b alleles.
This is one of the most important concepts in genetics. Your genotype is like your genetic recipe card - what's written in your DNA. Your phenotype is the actual cake that gets baked - what everyone can see and measure.
Two people can have the same phenotype but different genotypes. For example, both Sarah (BB) and her daughter (Bb) have brown eyes (same phenotype), but their genetic makeup is different (different genotypes).
BB = homozygous dominant
Bb = heterozygous
bb = homozygous recessive
These represent the actual alleles present in the organism's DNA.
These terms describe whether an organism has two identical alleles or two different alleles for a particular gene.
The prefix 'homo-' means 'same' and 'hetero-' means 'different'. So homozygous means having two identical alleles, while heterozygous means having two different alleles for the same gene.
Two identical dominant alleles (BB). The phenotype will definitely show the dominant trait. These individuals are 'pure-breeding' for the dominant trait.
One dominant and one recessive allele (Bb). The phenotype shows the dominant trait, but the recessive allele is carried and can be passed on.
Two identical recessive alleles (bb). The phenotype will show the recessive trait. These individuals can only pass on recessive alleles.
Punnett squares are like genetic calculators that help us predict what offspring might look like. They're named after Reginald Punnett, who developed this useful tool.
A Punnett square shows all possible combinations of alleles that offspring can inherit. You write one parent's alleles across the top and the other parent's alleles down the side, then fill in the squares to show all possible combinations.
The ability to roll your tongue is controlled by a dominant allele (R). If both parents are heterozygous (Rr), their Punnett square would show: 25% RR (can roll tongue), 50% Rr (can roll tongue) and 25% rr (cannot roll tongue). This gives a 3:1 ratio of tongue rollers to non-rollers.
Understanding how traits pass from parents to offspring helps us predict genetic outcomes and understand family similarities.
These involve studying the inheritance of just one characteristic at a time. They're perfect for understanding basic inheritance patterns and are the foundation for more complex genetic studies.
In pea plants, tall (T) is dominant over short (t). When a homozygous tall plant (TT) crosses with a homozygous short plant (tt), all offspring are heterozygous tall (Tt). When these Tt plants cross with each other, you get a 3:1 ratio of tall to short plants.
Genetic terminology isn't just for exams - it's used in medicine, agriculture and conservation to solve real problems and improve lives.
Doctors use genetic terminology to understand inherited diseases. For example, cystic fibrosis is a recessive condition, meaning both parents must carry the allele for a child to have the disease. Genetic counsellors use Punnett squares to help families understand their risks.
This condition shows how genetics can be complex. The sickle cell allele (S) is recessive for the disease but provides protection against malaria when heterozygous (AS). People with AS genotype have the sickle cell trait but not the disease and they're protected from malaria - showing how evolution can maintain harmful alleles in populations.
Certain genetic patterns appear repeatedly in inheritance studies. Recognising these patterns will help you solve genetic problems quickly and accurately.
3:1 ratio appears when crossing two heterozygotes
1:1 ratio appears in test crosses (heterozygote × homozygous recessive)
All offspring identical when crossing homozygous dominant × homozygous recessive