What Is the F2 Generation? - Definition & Characteristics

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  • 0:02 Mendelian Genetics
  • 1:33 Filial Groups: F1
  • 2:52 Filial Groups: F2
  • 4:22 Lesson Summary
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Lesson Transcript
Instructor: Sarah Phenix
In this lesson, we'll explore what an F2 generation is, how one arrives at this particular generation, and what the expected characteristics and distributions are among individuals.

Mendelian Genetics

What happens to the offspring if you breed two different colored flowers? And what happens to the offspring of those offspring?

You're probably familiar with monk and geneticist Gregor Mendel. It was through his work with pea plants that we first learned about genetics, the branch of biology that explores how genes dictate the characteristics of plants and animals.

Mendel didn't have any fancy equipment to help him determine a flower's genotype, or genetic makeup. All he had was the knowledge that, when he bred certain plants, the offspring had flowers of one color or they did not. From this he could work out if a flower was homozygous dominant, meaning it had two dominant alleles for one color; heterozygous, with one dominant allele and one recessive allele; or homozygous recessive, with two recessive alleles.

Mendellian genetics begins with cross-breeding two parents of homozygous genotypes. This is known as true breeding. True breeding refers to a purebred status, meaning you know what alleles it will pass on. In other words, while a heterozygous individual might pass on a dominant or recessive allele, a homozygous individual with the genotype BB can only pass on a B allele.

This is the first filial, or F1 generation. The F2 generation is the second filial generation of any cross-breed. What can we expect of the F2 generation in terms of characteristics, genetics, and distribution? Let's find out.

Filial Groups: F1

Let's say we are working with purple and white pea plants. We use a parental group or pair of true breeding individuals, so we know that one is purple and, therefore, homozygous dominant (BB), while the other is white and, therefore, homozygous recessive (bb). This variation ensures some level of genetic diversity in the F1 generation; otherwise we'd just end up with genetic clones, and what fun would that be?

Now we can create a Punnett square. One set of parental alleles is distributed across the top of the square, while the second runs along the side. By arranging them like this, we can distribute one allele per parent to each of the hypothesized four offspring. Now we know the genotypic distribution and can discern the phenotype, too. In other words, since all the offspring are heterozygous, they will all be purple.

Punnett squares illustrate what happens when two pairs of alleles are crossed
Punnett Square

In the case of two true breeding parents, we will always end up with heterozygous offspring, meaning they'll each have one dominant and one recessive allele. No matter how many times we crossed these individuals, we would never get any white flowers. One thing to keep in mind as we apply Mendelian genetics is that it doesn't allow for gene mutations. So what do we get if we cross the offspring?

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