lesson 2: inheritance
Key words:
-Allele
-Locus
-Dominant & Recessive
-Diploid & Haploid
-Carrier
A locus (plural: loci) is a specific location on a specific chromosome. The more commonly known loci are given a simple name, such as the A locus, the B locus, the Dw locus, or the En locus. Loci are specific locations for these specific genes. For example, the A locus is where agouti color is determined, and the Dw locus is where dwarfism is determined. For example, if your rabbit has a gene for agouti on the A locus, that means they are going to be an agouti colored rabbit.
Now because we've got pairs of chromosomes rather than singular chromatids, rabbits and humans are what's referred to as diploid organisms. Diploids get half of their chromosomes from their mother, and half from their father. The opposite of that would be haploids, such as most bacteria. Because rabbits get half of our genes from their mother and half from their father, each rabbit has two copies of every locus (one on each chromosome).
-Allele
-Locus
-Dominant & Recessive
-Diploid & Haploid
-Carrier
A locus (plural: loci) is a specific location on a specific chromosome. The more commonly known loci are given a simple name, such as the A locus, the B locus, the Dw locus, or the En locus. Loci are specific locations for these specific genes. For example, the A locus is where agouti color is determined, and the Dw locus is where dwarfism is determined. For example, if your rabbit has a gene for agouti on the A locus, that means they are going to be an agouti colored rabbit.
Now because we've got pairs of chromosomes rather than singular chromatids, rabbits and humans are what's referred to as diploid organisms. Diploids get half of their chromosomes from their mother, and half from their father. The opposite of that would be haploids, such as most bacteria. Because rabbits get half of our genes from their mother and half from their father, each rabbit has two copies of every locus (one on each chromosome).
NOTE: These are not the specific A, B, and C rabbit color genes. This is just a hypothetical example.
If we looked at, for example, just the A locus, there are a couple of different genes we could find. Let's say this hypothetical A locus determines whether the offspring is purple or not. There would have to be a gene for purple, and a different gene for not-purple. The word for these variant forms of genes is an allele. Rabbits have two alleles for every trait, one from each parent. The allele they get from a specific parent is randomly selected from the two alleles the parents possesses.
There are two types of alleles: dominant and recessive. Dominant alleles hide recessive alleles. Dominant alleles are denoted with capital letters, such as A, B, and C. Recessive alleles are 'weak', so they can be masked by their dominant counterpart. Recessive alleles are denoted with lowercase letters, like a, b, and c.
Let's take black and chocolate; the two basic coat colors. Black is dominant over chocolate, and is shortened to B. Chocolate is recessive, so it is shortened to b.
If a rabbit has two alleles for black (one from each parent), it would be BB, and be black in color. If a rabbit has two alleles for chocolate, it would be bb, and be chocolate in color.
But if a rabbit has one of each, or, Bb, the dominant B masks the recessive chocolate b, so the rabbit would be black, but 'carry' the chocolate gene that could be passed on to its offspring. This is called a chocolate carrier.
So if you breed a BB rabbit to a bb one, the offspring would all have Bb genotype, because they got a B gene from one parent, and a b gene from the other. The b would be masked by the B, so the resulting offspring would all have Bb genotype, and be black in color.
Oh, and one more thing. According to Mendel's Law of Independent Assortment, the alleles that an organism gets from each parent is RANDOM. So a rabbit with Bb genotype has a 50% chance of giving any given baby a B allele, and 50% chance of giving them a b allele. This is because of something called 'crossing over', which occurs when sex cells are produced. Basically the genes on a chromosome are shuffled to make sure the selection of genes is fairly random.
If we looked at, for example, just the A locus, there are a couple of different genes we could find. Let's say this hypothetical A locus determines whether the offspring is purple or not. There would have to be a gene for purple, and a different gene for not-purple. The word for these variant forms of genes is an allele. Rabbits have two alleles for every trait, one from each parent. The allele they get from a specific parent is randomly selected from the two alleles the parents possesses.
There are two types of alleles: dominant and recessive. Dominant alleles hide recessive alleles. Dominant alleles are denoted with capital letters, such as A, B, and C. Recessive alleles are 'weak', so they can be masked by their dominant counterpart. Recessive alleles are denoted with lowercase letters, like a, b, and c.
Let's take black and chocolate; the two basic coat colors. Black is dominant over chocolate, and is shortened to B. Chocolate is recessive, so it is shortened to b.
If a rabbit has two alleles for black (one from each parent), it would be BB, and be black in color. If a rabbit has two alleles for chocolate, it would be bb, and be chocolate in color.
But if a rabbit has one of each, or, Bb, the dominant B masks the recessive chocolate b, so the rabbit would be black, but 'carry' the chocolate gene that could be passed on to its offspring. This is called a chocolate carrier.
So if you breed a BB rabbit to a bb one, the offspring would all have Bb genotype, because they got a B gene from one parent, and a b gene from the other. The b would be masked by the B, so the resulting offspring would all have Bb genotype, and be black in color.
Oh, and one more thing. According to Mendel's Law of Independent Assortment, the alleles that an organism gets from each parent is RANDOM. So a rabbit with Bb genotype has a 50% chance of giving any given baby a B allele, and 50% chance of giving them a b allele. This is because of something called 'crossing over', which occurs when sex cells are produced. Basically the genes on a chromosome are shuffled to make sure the selection of genes is fairly random.