Genetics Answer Note #5

Question 1 Feather colour in parakeets is controlled by two genes. For one pigment gene, the B allele produces blue colour, and the b allele does not produce any colour at all. For the other pigment gene, the Y allele produces yellow colour, and the y allele does not produce any colour at all. Any genotype containing at least one B allele and one Y allele will produce a green parakeet. Which of the following parental genotypes could produce offspring displaying all four different colour patterns? Responses bbYY x bbyy bbYY x bbyy BbYY x Bvyy BbYY x Bvyy BBYy x BbYy BBYy x BbYy Bbyy x bbYy Answer Introduction: Parakeets are popular pets known for their vibrant colours, but have you ever wondered how their feather colour is controlled? It's actually controlled by two genes - one for pigment production and one for determining the colour of the pigment. In this answer, we will explore the different parental genotypes that can produce offspring with all four different colour patterns in parakeets. Understanding the Genes: Before we delve into the different parental genotypes, let's first understand the two genes involved in parakeet feather colour - B and Y. The B gene is responsible for pigment production, with the B allele producing blue colour and the b allele producing no colour at all. Similarly, the Y gene determines the colour of the pigment, with the Y allele producing yellow colour and the y allele producing no colour at all. Producing Offspring with All Four Colour Patterns: Based on the information provided, we know that any genotype containing at least one B allele and one Y allele will produce a green parakeet. Therefore, the parental genotypes that could produce offspring displaying all four different colour patterns are: 1. BBYY x BBYY 2. BBYY x BbYY 3. BBYY x bbYY 4. BBYY x BBYy 5. BbYY x BbYY 6. BbYY x BbYy 7. BbYY x bbyy Explanation: It may seem overwhelming to see so many different genotypes, but let's break it down step by step. Let's take the first parental genotype, BBYY x BBYY. In this case, both parents have the dominant alleles for both genes - B for pigment production and Y for determining the colour of the pigment. Therefore, all offspring from this pairing will inherit the dominant alleles from both parents, resulting in green parakeets. Similarly, when we look at the second parental genotype, BBYY x BbYY, we can see that one parent has both dominant alleles (BBYY) while the other has one dominant and one recessive allele (BbYY). This means that half of the offspring will inherit the dominant alleles and the other half will inherit one dominant and one recessive allele, resulting in green and blue parakeets respectively. When we apply this logic to the remaining five parental genotypes, we can see that all of them have the potential to produce offspring with all four different colour patterns. This is because they all have at least one parent with dominant alleles for both genes, ensuring that all offspring will inherit at least one B allele and one Y allele. Conclusion: In conclusion, there are several parental genotypes that can produce offspring with all four different colour patterns in parakeets. These include: BBYY x BBYY, BBYY x BbYY, BBYY x bbYY, BBYY x BBYy, BbYY x BbYY, BbYY x BbYy, and BbYY x bbyy. With a good understanding of the two genes involved in parakeet feather colour, we can determine the potential offspring colours from different parental genotypes. Question 2 a 9:3:3:1 ratio of phenotype should be observed from what parents? Answer The 9:3:3:1 ratio, also known as the dihybrid ratio, is a fundamental concept in genetics that describes the expected phenotypic ratios that result from a cross between two individuals who are heterozygous for two traits that are located on different chromosomes. This ratio is based on the principles of Mendelian genetics and can be observed in a variety of organisms, including plants and animals. To understand which type of parents would produce this ratio, we first need to have a clear understanding of the factors involved in this type of cross. According to Mendel's laws of inheritance, traits are determined by the presence of alleles, or alternative versions of a gene, which can be dominant or recessive. When two individuals who are heterozygous for two different traits are crossed, each parent can contribute different combinations of alleles, which will determine the phenotype of the offspring. In the case of a 9:3:3:1 ratio, this can be achieved when both parents are heterozygous for both traits (AaBb x AaBb). In this type of cross, the genotype ratio would be 1:2:1, meaning that for every 1 offspring that is homozygous dominant (AA, BB), there will be 2 offspring that are heterozygous (Aa, Bb) and 1 offspring that is homozygous recessive (aa, bb). This genotype ratio will then translate into a phenotypic ratio of 9:3:3:1, with 9 offspring showing both dominant traits (A_B_), 3 offspring showing one dominant and one recessive trait (A_bb or aaB_), 3 offspring showing the other dominant and recessive trait (aaB_ or A_bb), and 1 offspring showing both recessive traits (aabb). Question 3 Determine the genotypic and phenotypic ratio of the offspring of a red 4 o‘clock flower and a white 4 o‘clock flower. Answer According to Mendelian genetics, the genotypic ratio of the offspring from a cross between a red 4 o'clock flower (RR) and a white 4 o'clock flower (WW) would result in a heterozygous (RW) offspring. This means that the genotypic ratio of the offspring would be 1:0:1, with one being homozygous dominant for red (RR), zero being homozygous recessive for white (WW), and one being heterozygous for red and white (RW). As for the phenotypic ratio, there are two possible outcomes: all red flowers or a mixture of red and white flowers. This is because the red color is dominant over white. Therefore, the phenotypic ratio would either be 1:0 (all red) or 1:1 (mix of red and white) depending on whether the heterozygous offspring (RW) produces red or white pigments. To further explain the outcome of the heterozygous offspring, we can use a Punnett square. In this case, the parental traits would be represented as R and W, with uppercase letters representing dominant traits and lowercase letters representing recessive traits. Possible genotypes of the offspring: RR (homozygous dominant for red) RW (heterozygous for red and white) WW (homozygous recessive for white) Possible phenotypes of the offspring: Red 4 o'clock flower (RR or RW) White 4 o'clock flower (WW) If we cross a red 4 o'clock flower (RR) with a white 4 o'clock flower (WW), the resulting offspring would all be heterozygous (RW) for the gene responsible for color. However, as an exception, there is a chance of mutation resulting in a completely new color. In this case, it is best to consider only the dominant and recessive alleles to calculate the genotypic and phenotypic ratio. Question 4 In humans, six fingers (F) is the dominant trait, and five fingers (f) is the recessive trait. If the father is heterozygous for six fingers and the mother has five fingers, what is the probability of having five and six fingered children? Answer To accurately answer this question, we first need to understand the basic principles of genetics and how traits are inherited. In humans, each individual has two copies of a gene, one inherited from each parent. These gene copies are called alleles, and they can be either dominant or recessive. The dominant allele is expressed and determines the physical trait, while the recessive allele is only expressed when the individual has two copies of it. In the case of finger number, the allele for six fingers (F) is dominant, and the allele for five fingers (f) is recessive. This means that if an individual has at least one F allele, they will have six fingers. However, if they inherit two copies of the f allele, they will have five fingers. Now, let's apply this knowledge to the given scenario. The father is heterozygous, meaning he has one copy of the dominant F allele and one copy of the recessive f allele. The mother, on the other hand, has two copies of the recessive f allele. The probability of their children having five fingers is 25% (1 out of 4) since both parents must pass on the f allele for their child to have five fingers. Similarly, the probability of their children having six fingers is also 25% (1 out of 4) since there is a 50% chance of inheriting the F allele from the father and a 50% chance of inheriting the f allele from the mother. To further understand this concept, we can use a Punnett square diagram to visually represent the possible combinations of alleles in the offspring. The diagram would look like this: Father: Ff Mother: ff Ff F FF Ff f Ff ff From this Punnett square, we can see that there is a 50% chance of the child inheriting one F allele from the father and one f allele from the mother, resulting in six fingers. There is also a 50% chance of the child inheriting two f alleles, resulting in five fingers. Question 5 researcher is trying to determine the mode of inheritance that contributes to the colour of a new species of insect that uses XY chromosomes to determine biological sex. Three colours appear to be present; yellow, blue, and green. Assume that the first locus is autosomal and exhibits dominant epistasis over the second locus to produce the blue colour and that the second locus is located on the X chromosome. The homozygous recessive phenotype results in a green colour. Write the genotypes of a fully heterozygous blue female and heterozygous male that has the dominant allele present on the X chromosome. (2 marks) Write a legend for the possible genotypes and resulting phenotypes using an underscore (_) to represent any allele. The first example has been done for you. Answer Based on the given information, the genotype of a fully heterozygous blue female would be AXB_, where A represents the dominant allele for the first locus and B represents the dominant allele for the second locus on the X chromosome. The genotype of a heterozygous male with the dominant allele on the X chromosome would be AYB_, where A represents the dominant allele for the first locus and B represents the dominant allele for the second locus on the X chromosome, while Y represents the male sex chromosome. Legend for possible genotypes and resulting phenotypes: 1. AXBX_ = Blue colour phenotype 2. AYBX_ = Blue colour phenotype 3. AXBY_ = Blue colour phenotype 4. AYBY_ = Blue colour phenotype 5. axbX_ = Yellow colour phenotype 6. axbY_ = Yellow colour phenotype 7. axbx_ = Green colour phenotype 8. axby_ = Green colour phenotype