How to Work With Punnett Squares
Understand the concept of genes., Understand the concept of sexual reproduction., Understand the concept of alleles., Understand the concept of dominant and recessive alleles.
Step-by-Step Guide
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Step 1: Understand the concept of genes.
Before learning how to make and use Punnett squares, it's necessary to get some important basics out of the way.
The first is the idea that all living things (from tiny microbes to giant blue whales) have genes.
Genes are incredibly complex, microscopic sets of instructions encoded into almost every single cell in an organism's body.
Genes are responsible, in some way, for virtually every aspect of an organism's life, including the way it looks, the way it behaves, and much, much more.
One concept that's important to understand when working with Punnett squares is that living things get their genes from their parents.You are probably already aware of this subconsciously.
Think — don't the people you know seem to be similar to their parents in the way they look and act, generally? , Most (but not all) of the organisms you are aware of in the world around you make children via sexual reproduction.
That is, a female parent and a male parent each contribute their genes to make a child with about half of its genes from each parent.
A Punnett square is basically a way of showing the different possibilities that can occur from this half-and-half exchange of genes in the form of a graph.
Sexual reproduction isn't the only form of reproduction out there.
Some organisms (like many strains of bacteria) reproduce via asexual reproduction, which is when one parent makes a child all by itself.
In asexual reproduction, all of the child's genes come from one parent, so the child is more or less a copy of its parent. , As mentioned above, an organism's genes are basically a set of instructions that tell every cell in the organism's body how to live.
In fact, just like an instruction manual is divided into different chapters, sections, and subsections, different parts of an organism's genes tell it how to do different things.
If one of these "subsections" is different between two organisms, the two organisms may look or behave differently — for instance, genetic differences may lead one person to have black hair and another to have blonde hair.
These different forms of the same gene are called alleles.
Because a child gets two sets of genes — one from each parent — it will have two copies of every allele. , A child's alleles do not always "share" their genetic power.
Some alleles, called dominant alleles, will manifest in the child's looks and behavior (we call this "being expressed") by default.
Others, called recessive alleles, will only be expressed if they're not paired with a dominant allele which can "override" them.
Punnett squares are often used to help determine how likely a child is to receive a dominant or recessive allele.
Because they can be "overridden" by dominant alleles, recessive alleles tend to be expressed more rarely.
In general, a child will have to get a recessive allele from both parents for the allele to be expressed.
A blood condition called sickle-cell anemia is a frequently-used example of a recessive trait — note, however, that recessive alleles aren't "bad" by definition. -
Step 2: Understand the concept of sexual reproduction.
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Step 3: Understand the concept of alleles.
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Step 4: Understand the concept of dominant and recessive alleles.
Detailed Guide
Before learning how to make and use Punnett squares, it's necessary to get some important basics out of the way.
The first is the idea that all living things (from tiny microbes to giant blue whales) have genes.
Genes are incredibly complex, microscopic sets of instructions encoded into almost every single cell in an organism's body.
Genes are responsible, in some way, for virtually every aspect of an organism's life, including the way it looks, the way it behaves, and much, much more.
One concept that's important to understand when working with Punnett squares is that living things get their genes from their parents.You are probably already aware of this subconsciously.
Think — don't the people you know seem to be similar to their parents in the way they look and act, generally? , Most (but not all) of the organisms you are aware of in the world around you make children via sexual reproduction.
That is, a female parent and a male parent each contribute their genes to make a child with about half of its genes from each parent.
A Punnett square is basically a way of showing the different possibilities that can occur from this half-and-half exchange of genes in the form of a graph.
Sexual reproduction isn't the only form of reproduction out there.
Some organisms (like many strains of bacteria) reproduce via asexual reproduction, which is when one parent makes a child all by itself.
In asexual reproduction, all of the child's genes come from one parent, so the child is more or less a copy of its parent. , As mentioned above, an organism's genes are basically a set of instructions that tell every cell in the organism's body how to live.
In fact, just like an instruction manual is divided into different chapters, sections, and subsections, different parts of an organism's genes tell it how to do different things.
If one of these "subsections" is different between two organisms, the two organisms may look or behave differently — for instance, genetic differences may lead one person to have black hair and another to have blonde hair.
These different forms of the same gene are called alleles.
Because a child gets two sets of genes — one from each parent — it will have two copies of every allele. , A child's alleles do not always "share" their genetic power.
Some alleles, called dominant alleles, will manifest in the child's looks and behavior (we call this "being expressed") by default.
Others, called recessive alleles, will only be expressed if they're not paired with a dominant allele which can "override" them.
Punnett squares are often used to help determine how likely a child is to receive a dominant or recessive allele.
Because they can be "overridden" by dominant alleles, recessive alleles tend to be expressed more rarely.
In general, a child will have to get a recessive allele from both parents for the allele to be expressed.
A blood condition called sickle-cell anemia is a frequently-used example of a recessive trait — note, however, that recessive alleles aren't "bad" by definition.
About the Author
Beverly Collins
Professional writer focused on creating easy-to-follow home improvement tutorials.
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