Mendelian Genetics
Task 1 (P4)
Draw annotated diagrams to show and describe what would happen during each stage of meiosis if a crossover occurred between the chromosomes shown.
Attached to assignment
Use diagrams to help explain how variation will occur in the offspring when each gamete formed fuses with another that has the genotype ab. (Account for all possible offspring)
It’s a known fact that genetic variation does happen throughout the stages of meiosis. The first stage of meiosis is called prophase I, and during this stage homologous chromosomes pair up. When they pair up they form bivalents. Chromosomes move around a cells cytoplasm and when they do they become tangled, in a process called a cross over.
Variation will occur in the offspring for two reasons. First of all, the new chromosomes that will be created will create different gametes to the parental (original) gametes. Second of all, there will be a high range of different gametes produced, and this will cause more diversities in the offspring. Since the newly produced gametes are heterozygous, and are carriers of different alleles, they will pass over different genes to their offspring. The creation of these new gametes will give the offspring a greater chance of variation.
Task 2 (P5)
Use the software Droslab to carry out simulations of the following crosses in Drosophila melanogaster and attach the results of the simulations to this assignment:
Monohybrid cross (Wing size)
Dihybrid cross (Wing size and Body colour)
Linked inheritance cross (Body colour and Curly wings)
Explain the ratio of characteristics observed in the offspring for each cross.
Experiment 1: In the parental (F1) cross, the ratio of wild to vestigial flies was 1:0, and this was excepted, and comes as no surprise to me because the gene for vestigial flies is recessive. In fact, the two parent flies were wild, so it wasn’t likely for a vestigial fly to be produced, especially when you consider that the parents weren’t even carriers of the recessive gene. In the hybrid cross, both parents were carriers of the “vestigial” gene, so there was a possibility that their offspring could be vestigial. Nevertheless, you would except more wild flies than vestigial flies. The excepted ratio of wild: vestigial flies is 3:1. This tells me that there a 3 in 1 chance that the offspring will inherit the dominant (wild) gene. In the cross that I made for my simulation, the ratio was approximately 2.5:1. I was happy with the ratio that I got because it was very close to the excepted ratio.
Experiment 4: The ratio of wild to mutant flies was 1:0. This was the excepted and observed ratio. I think that no mutant flies were produced because the parent flies were wild, and their offspring inherited the dominant (wild) gene. In the hybrid cross, there should be more mutant flies, which would range from vestigial flies, ebony flies, and vestigial and ebony. The excepted ratio is 9:3:3:1, because crossing over will occur in the genes from the parents, and: this will cause more diversity in their offspring. There may be a slight variation from the expected ratio, but my observed ratio does follow this in a sort of way.
Experiment 10: The parent process is a 1:0 ratio, of wild flies compared to the mutant flies. The hybrid cross will have the ratio 9:3:3:1, because of the crossover of the genes from the parents. Crossing over will cause more recessive genes to be expressed and more phenotypes will be expressed. My hybrid cross did not have the same ratio. In fact, the ratio was 6:3:2:4. I think this was because of the size of my sample. Perhaps 200 flies were not a large enough sample to obtain an accurate ratio.
Task 3 (For M3)
Complete the questions on the simulation experiment sheets to comment on crosses involving independent and linked genes.
Attached to assignment
Cystic fibrosis is a condition in humans that leads to a build-up of thick, sticky mucus in the lungs and digestive system. It is caused by a recessive mutation of the CFTR gene, which codes for chloride channels in cell membranes.
Produce punnet squares to predict the inheritance patterns of cystic fibrosis in the following situations:
Show the phenotypes and genotypes of all possible offspring.
Homozygous dominant x Heterozygous
Genotype
Cc- Heterozygous
CC- Homozygous Dominant
Offspring Genotypes Gametes- Homozygous Dominant
Gametes- Heterozygous C C
C CC CC
c Cc Cc
Offspring Phenotypes
50% carrier
50% normal person (no cystic fibrosis)
Heterozygous x Heterozygous
Genotype
Cc- Heterozygous
Offspring Genotypes Gametes- Heterozygous
Gametes- Heterozygous C c
C CC Cc
c Cc cc
Offspring Phenotypes
25% normal person- no cystic fibrosis
50% carrier of cystic fibrosis
25% cystic fibrosis sufferer
Haemophilia is a recessive X-linked condition in humans that leads to a lack of coagulating (‘clotting’) agents in the blood.
Produce punnet squares to predict the inheritance patterns of haemophilia in the following situations:
Female carrier x Male haemophiliac
Female Carrier- Phenotype
XH Xh – Genotype
Male Haemophiliac-Phenotype
Xh Y – Genotype
Gametes
Female Carrier – XH Xh
Male Haemophiliac- Xh Y
Offspring genotypes Gametes- Male Haemophiliac Gametes- Female Carrier Xh Y
XH XH Xh XH Y
Xh Xh Xh Xh Y
Offspring phenotypes
25% female carrier
25% Normal Male
25% Haemophiliac male
25% Haemophiliac female
Female haemophiliac x ‘Healthy’ male
Phenotype- Female haemophiliac
Genotype- Xh Xh
Phenotype- Healthy male
Genotype- XH Y
Gametes- Xh and Xh-Female
XH and Y-Male
Offspring Genotypes Gametes-Male Gametes-Female XH Y
Xh XH Xh Xh Y
Xh XH Xh Xh Y
Offspring phenotypes
50% female carrier
50% haemophiliac male
‘Healthy’ (non-carrier) female x Male haemophiliac
Phenotype- Healthy (non-carrier) female
Genotype- XH XH
Phenotype- Male haemophiliac
Genotype- Xh Y
Gametes- XH and XH-Female
Xh and Y-Male
Offspring Genotypes Gametes-Male haemophiliac Gametes- Healthy Female Xh Y
XH XH Xh XH Y
XH XH Xh XH Y
Offspring Phenotype/Genotype
50% female carrier-XH Xh
50% healthy male- XH Y
Task 4 (For D2)
Refer to your results from the Drosophila simulations.
Perform chi-squared analysis on the data from the three crosses observed.
Discuss the validity of your findings and factors that may have affected this.
2.
As you can see from my chi-squared test, my chi squared value for experiment 1 was 1.3, and my chi squared value for experiment four was 35.3.
