16.2. The roles of genes in determining the phenotype
A subsection of Biology, 9700, through 16. Inheritance
Listing 10 of 116 questions
The fruit fly, Drosophila melanogaster, usually has red eyes. A gene for eye colour has four alleles: red, apricot, honey and white. Define the terms gene and allele. gene allele • The allele for red eyes, CR, is dominant to the other three alleles. • The allele for apricot eyes, CA, is dominant to the allele for honey eyes, CH. • The allele for white eyes, CW, is recessive to the other three alleles. Construct a genetic diagram to show the genotypes, phenotypes and ratio of the offspring from a cross between a fruit fly with red eyes, CRCH, and a fruit fly with apricot eyes, CACW. parents phenotypes red eyes apricot eyes parents genotypes CRCH CACW gametes offspring genotypes offspring phenotypes ratio Describe how you would carry out a test cross and use it to determine the genotype of a red- eyed fruit fly.
9700_s22_qp_41
THEORY
2022
Paper 4, Variant 1
View
Epistasis occurs when a gene at one locus can affect the expression of a gene at another locus. Define the terms gene and locus. gene locus Fur colour in mice, Mus musculus, is determined by a number of genes. One example is the result of epistatic interaction between two genes, A and B. • Allele A codes for the production of pigment in the fur. • Allele a does not code for the production of pigment and results in white fur . • Allele B codes for the production of brown fur. • Allele b codes for the production of black fur. Construct a genetic diagram to show the results, including the ratio, of a cross between two mice heterozygous for both genes. parent genotypes AaBb x AaBb parent phenotypes gametes ratio White fur is due to a mutation of the TYR gene. This is called albinism. Explain how a mutation of the TYR gene can result in albinism.
9700_s22_qp_43
THEORY
2022
Paper 4, Variant 3
View
In mice there are several alleles of the gene that controls the intensity of pigmentation of the fur. The alleles are listed below in order of dominance with C as the most dominant. C = full colour Cch = chinchilla Ch = himalayan Cp = platinum Ca = albino The gene for eye colour has two alleles. The allele for black eyes, B, is dominant, while the allele for red eyes, b, is recessive. A mouse with full colour and black eyes was crossed with a himalayan mouse with black eyes. One of the offspring was albino with red eyes. Using the symbols above, draw a genetic diagram to show the genotypes and phenotypes of the offspring of this cross.
9700_w08_qp_4
THEORY
2008
Paper 4, Variant 0
View
In mice, fur colour is controlled by a gene with multiple alleles. These alleles are listed below in no particular order. black and tan = Cbt yellow = Cy agouti = Ca black = Cb Suggest explanations for the results of the following crosses between mice. Mice with agouti fur crossed with mice with black fur may produce all agouti offspring or some agouti and some black offspring. Crosses between heterozygous parents with the genotype Cy Cb always produce a ratio of two yellow mice to one black mouse. Mice with yellow fur crossed with mice with black fur will produce one of the following outcomes: • some yellow offspring and some agouti offspring • some yellow offspring and some black and tan offspring • some yellow offspring and some black offspring. A test cross is used to determine the genotype of an organism. Describe how you would carry out a test cross to determine the genotype of a black and tan mouse.
9700_w12_qp_43
THEORY
2012
Paper 4, Variant 3
View
The fruit fly, Drosophila melanogaster, is widely used in genetic research. It has many phenotypic variants in features such as body colour, wing shape and eye colour. Two variations from the normal-winged, grey-bodied phenotype are: • vestigial (very short) wings, coded for by the recessive allele of the gene N/n • ebony body colour, coded for by the recessive allele of the gene G/g. Using the symbols given, state the possible genotypes of normal-winged, grey-bodied fruit flies. Describe how you would determine the genotype of a normal-winged, grey-bodied fly. One of the genes for eye colour is carried on the X chromosome. This gene has different alleles coding for: • red eyes • orange eyes • white eyes. The allele for red eyes (R) is dominant to the allele for orange eyes and dominant to the allele for white eyes . The allele for orange eyes is dominant to that for white eyes. Using these symbols, draw a genetic diagram to show how a cross between a white-eyed male fruit fly with a red-eyed female fruit fly will produce male and female offspring that are either red-eyed or orange-eyed.
9700_w15_qp_43
THEORY
2015
Paper 4, Variant 3
View
The Labrador retriever is a modern breed of dog that can have yellow, black or brown fur and pale, black or brown noses. The inheritance of fur and nose colour is the result of the interaction between genes at two different loci, the B locus and the E locus. shows a Labrador retriever. Table 1.1 shows how gene interaction results in different phenotypes. Table 1.1 alleles at B locus alleles at E locus phenotype B_ ee yellow fur black nose bb ee yellow fur pale nose B_ E_ black fur black nose bb E_ brown fur brown nose A male Labrador retriever, heterozygous at the B locus and homozygous recessive at the E locus, was mated with a female Labrador retriever heterozygous at both loci. Explain the terms locus and homozygous. locus homozygous Use a genetic diagram to show the possible genotypes and phenotypes of the offspring from the mating between the two Labrador retrievers. parental phenotypes parental genotypes gametes offspring genotypes and phenotypes
9700_w16_qp_43
THEORY
2016
Paper 4, Variant 3
View
The sweet pea, Lathyrus odoratus, is a flowering plant that grows in many parts of Europe. The inheritance of flower colour and shape of pollen grains is controlled by genes that display autosomal linkage. Explain what is meant by autosomal linkage. In sweet peas, the allele for purple flowers is dominant to the allele for red flowers and the allele for long pollen grains is dominant to the allele for round pollen grains. A sweet pea plant that is heterozygous for both purple flowers and long pollen grains is crossed with a sweet pea plant with red flowers and round pollen grains. The results of this cross are shown in Table 8.1. Table 8.1 offspring phenotype percentage of offspring purple flowers, long pollen grains red flowers, round pollen grains purple flowers, round pollen grains red flowers, long pollen grains Describe and explain the results shown in Table 8.1. Different alleles affecting flower colour in the sweet pea plant are the result of gene mutations. State how a gene mutation may occur.
9700_w17_qp_42
THEORY
2017
Paper 4, Variant 2
View
Questions Discovered
116