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Mendel's First Law: The Law of Segregation

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  • 0:45 Mendel's Experiments
  • 1:47 Alleles Associated…
  • 3:37 Alleles Segregate
  • 4:45 Lesson Summary
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Lesson Transcript
Instructor: Greg Chin
Breaking up is a hard thing to do, but homologous chromosomes always go their separate way. What effect does chromosome segregation have on genetics? We look once more to Adrian's flying hamsters for answers.

Further Flying Hamster Research

We've been studying flying hamster coat color with our scientist friend, Adrian. We've learned that the brown coat phenotype is dominant over the white coat phenotype. Now, when we say dominant, what we mean is that when the coat color gene is heterozygous for these alleles, the hamster will be brown. We know this because 'BB' and 'Bb' genotypes produce brown hamsters, and 'bb' genotype produces white hamsters. And in drawing these conclusions from our mating experiment, we've observed Mendel's first law.

Mendel's Experiments

Austrian monk Gregor Mendel studied pea plant genetics in the 1800s
Gregor Mendel

Gregor Mendel was an Austrian monk who studied pea plant genetics in the 1800s. Mendel's experiments provided quantitative data, which would eventually revolutionize the understanding of the inheritance of traits. Unfortunately for poor Mendel, his findings were largely ignored until 1900, when the observation of meiosis helped scientists realize the significance of Mendel's experiments.

Mendel's laws helped explain chromosome-based inheritance of traits. Mendel is also credited with identifying the concept of dominant and recessive traits. We've already seen how a dominant trait affected Adrian's flying hamster experiment.

Now we're going to examine Mendel's first law of inheritance, also known as Mendel's law of segregation. It states that, ' the alleles of a given locus segregate into separate gametes.'

So let's see how the law of segregation applies to our hamster genetics experiments.

Alleles Associated with Chromosomes

We learned that an animal with a homozygous dominant genotype ('BB') will produce a hamster that is brown. We also know that if we have a heterozygous genotype ('Bb'), we will also produce a hamster that is brown. However, if we have a hamster that has a 'bb' genotype (homozygous recessive), it will produce a hamster that is white.

Organisms with homozygous dominant or heterozygous genotypes will display the dominant trait
Genotypes

We also know that genes are associated with a specific chromosome. For a flying hamster, we have three different chromosomes. Let's say that we discover that the coat color gene is located on chromosome three.

We also have to remember that the flying hamster, like most animals, is a diploid organism. What this means is that we actually have two copies of chromosome three in any given cell in the hamster's body. If you remember, the different versions of a gene are referred to as an allele, so each chromosome three could potentially have a different allele associated with it.

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