Heredity and Traits
Grade 6 · Science · Study Guide
Discover how traits are passed from parents to offspring through genes and DNA.
Have you ever noticed that you share features with your parents or grandparents? Maybe you have your mom's eyes or your dad's nose. This passing of traits from parents to offspring is called heredity. The science of heredity is called genetics.
Traits are characteristics, like eye color, hair texture, or blood type. Physical traits are controlled by genes — segments of DNA found on chromosomes inside the nucleus of every cell. Humans have 46 chromosomes (23 pairs) in almost every cell. One chromosome in each pair comes from your mother and one from your father.
Each gene can come in different versions called alleles. Some alleles are dominant — they mask the effect of the other allele whenever present. Other alleles are recessive — they only show up when two copies of the recessive allele are present. Gregor Mendel, a 19th-century monk, figured out these rules by breeding pea plants and counting thousands of offspring. He is called the Father of Genetics.
For example, the allele for brown eyes (B) is dominant over the allele for blue eyes (b). If you inherit one B and one b (written Bb), you'll have brown eyes because B is dominant. Only someone who inherits two b alleles (bb) will have blue eyes. Scientists use a Punnett square — a grid — to predict the probability of offspring inheriting certain trait combinations.
| Genotype | Alleles Present | Phenotype (Eye Color Example) |
|---|---|---|
| BB | Two dominant | Brown eyes |
| Bb | One dominant, one recessive | Brown eyes (dominant shown) |
| bb | Two recessive | Blue eyes |
Key terms
- Heredity
- The passing of traits from parents to offspring through genes.
- Gene
- A segment of DNA that codes for a specific trait.
- Allele
- A version of a gene; one inherited from each parent.
- Dominant
- An allele that is expressed whenever it is present, masking the recessive allele.
- Recessive
- An allele that is only expressed when two copies are present (no dominant allele).
- Genotype
- The genetic makeup of an organism (e.g., Bb or bb).
- Phenotype
- The observable physical trait resulting from the genotype (e.g., brown eyes).
- Punnett square
- A grid used to predict the probability of offspring inheriting specific allele combinations.
Flashcards
- Heredity
- The passing of genetic traits from parents to their offspring.
- Gene
- A DNA segment that determines a specific trait; located on chromosomes.
- Allele
- Alternative forms of a gene (e.g., B for brown eyes, b for blue).
- Dominant allele
- Expressed whenever present; masks the recessive allele.
- Recessive allele
- Only expressed when two copies are present (no dominant allele).
- Punnett square
- A grid that predicts the probability of allele combinations in offspring.
Practice questions
What is a gene?
- A type of chromosome
- A segment of DNA that codes for a specific trait
- A protein in the cell membrane
- A type of allele
Show answer
Answer: A segment of DNA that codes for a specific trait
Genes are the instructions written in DNA that tell cells how to build proteins, which in turn determine traits.
A recessive allele is expressed only when two copies of it are present.
Show answer
Answer: True
A recessive allele like 'b' for blue eyes only shows up in the phenotype when the genotype is 'bb' — no dominant allele is present to mask it.
The physical trait produced by an organism's genotype is called its ___.
Show answer
Answer: phenotype
The phenotype is what you can see or measure — eye color, hair texture, height. The genotype is the underlying genetic code.
Who is known as the Father of Genetics for his work with pea plants?
- Charles Darwin
- Isaac Newton
- Gregor Mendel
- Louis Pasteur
Show answer
Answer: Gregor Mendel
Mendel's careful experiments with pea plant traits in the 1860s established the fundamental laws of inheritance, earning him the title Father of Genetics.
If an organism has genotype Bb and B is dominant, its phenotype will show the recessive trait.
Show answer
Answer: False
In genotype Bb, B is dominant and will be expressed. The organism will show the dominant phenotype (e.g., brown eyes), not the recessive one.
Fun facts
- Gregor Mendel studied about 29,000 pea plants over 8 years to work out the laws of heredity — all without knowing DNA even existed.
- Identical twins have nearly identical DNA, but they can still have different fingerprints because fingerprints are also shaped by conditions in the womb.
- You share about 99.9% of your DNA with every other human on Earth — the 0.1% difference accounts for all the variation you see.
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