Developing Skills Flashcards
Explain the relationship between the sequence of bases in DNA, a gene and alleles.
A gene is a section of DNA that codes for a trait. This means the gene gives the instructions for the organism to make that trait. For example, the gene for hair colour tells an organism how to make hair that is coloured. Alleles are different versions of a gene that code for different versions of the trait. For example, a gene for hair colour might have two alleles, one that gives brown hair, and one that gives blonde hair. The sequence of bases in a gene is important because a different order of bases can result in a different trait. If the sequence is only a little different, you get a different allele that produces a different version of the same trait. However, different genes (coding for different traits) have very different base sequences to each other.
Think about base sequences as being like using a recipe to bake a cake - you have to mix together your dry ingredients with the wet, put it into the cake pan, and then put it into the oven. You need to follow the steps of the recipe in the right order, or you will get a different product. If you put the dry ingredients straight in the oven and add wet ingredients at the end, you certainly won’t get a cake! A gene is similar - the order of the bases is important, but in the case of a gene, we are making a protein (not a cake). Different sequence of bases, different protein.
However, if we only modify the recipe slightly (change a few bases in the sequence), we get a similar product. Alleles are like recipes coding for slightly different cake varieties like a recipe for chocolate cake versus one for banana. Both give you a cake at the end, but the cakes produced are a little bit different because the recipes were a little bit different.
Completely different genes have very different base sequences. For example, the gene for eye colour has a very different sequence of bases to the gene for hair colour. This is similar to how the recipe to make minestrone soup is quite different to the recipe to make a tasty cake!
Explain how different alleles for a gene differ from each other?
Different alleles for the same gene have a very similar sequence of bases, with just one or a few differences.
Explain how a mutation can create a new allele.
A mutation is any change to the sequence of bases. Changing the sequence of bases can change the trait that the gene codes for (see the explanation for the question above), so a mutation can change what a gene codes for, and creates a new allele. This is where all new alleles come from.
A single gene can have two or more alleles. A single chromosome can carry multiple genes, each with its own set of alleles. Explain:
a. How do different genes differ from each other?
b. What is the difference between a gene and allele at the DNA level?
a. Different genes have different sequences of bases so they give instructions for making different traits.
b. A gene will be at the same loci (location) on the chromosome. An allele refers to a different base sequence within that gene.
Explain how genes and alleles are linked to genotype, and how all three are linked to phenotype.
he genotype is the combination of alleles an organism has for each gene. The genotype is responsible for the phenotype of the organism. This is because each gene encodes a trait, giving
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Level 1 Science| Genetics | Answers |© Inspiration Education Limited 2022. All rights reserved.ed. 13
the instructions for the organism’s body to produce the trait. Alleles are different versions of the gene which code for slightly different versions of the trait, such as brown hair versus black hair. If the genotype of the organism is different, this means it has a different combination of alleles. This may mean that it has a different phenotype, since it has a different set of instructions to produce its traits. For example, if B is the allele for brown eyes and b for blue eyes, an organism with genotype BB has brown eyes but an organism with genotype bb has blue eyes. Alleles can be dominant or recessive. The trait that a dominant allele codes for will always show up in the phenotype. The trait that a recessive allele codes for will only show up in the phenotype if the genotype is homozygous. The environment that an organism lives in also influences the phenotype, and some traits in the phenotype such as scars or missing limbs are not encoded in the genes. The genotype is not directly responsible for these traits.
Explain the relationship between chromosomes, and DNA, genes and alleles.
DNA is a molecule made up of sugar, phosphate, and four different bases - A, T, G, and C. The DNA molecule has a double-helix shape and encodes the genetic information, which means it is responsible for the different traits of the organism. A chromosome is one long DNA molecule, which can have several genes on it. A gene is a section of DNA coding for a trait. This means the gene provides the instructions for the organism to make that trait. Alleles are different versions of the gene and they code for different versions of the trait. For example, a gene for hair colour might have two alleles, one that gives brown hair, and one that gives blonde hair.
