bio genetics - P2 (13)
Two alleles of a gene influence body colour in Drosophila.
brown body vestigial wings AND black body, normal wings
Explain whether these results fit the predicted Mendelian ratios for this cross.
independent assortment predicts 1:1:1:1
suggests linkage
State the genotype of the F1 hybrids.
CcRr/RrCc
Explain how the pattern of inheritance results in the 9:7 ratio in the F2 generation
purple if at least one dominant allele of both genes
white if either gene is homozygous recessive / with either cc_ _ or _ _rr
1 (of 16) is white with ccrr
Explain the conclusion that can be drawn from Cross 1.
allele for banded is dominant + allele for unbanded is recessive;
because two banded spiders produced some unbanded offspring
both parents are heterozygous;
ratio 3 : 1
Deduce reasons for the difference between the results of Cross 2 and Cross 3.
1:1 ratio) in cross 2 as banded parent is heterozygous/has one copy of each allele;
c. (in crosses 2 and 3) banded parental phenotypes are the same but their genotypes are
different;
There were 79 progeny in Cross 4. Predict the expected results by completing the table.
0
79
0.000/0
The proportion of banded and unbanded individuals in a population of D. plantarius can change. Suggest how such a change could occur.
natural selection could favour one type over the other;
State how many chromosomes there would be in male or female gametes of L. purpureus
12
Suggest a reason for the F2 generation not corresponding exactly to the expected ratio of purple-flowered and white-flowered plants.
Any wording that implies the bigger the sample size, the closer to 3:1.
Calculate the probability of male Y having an allele for the disorder.
50%/ 0.5/ 1/2;
Explain how the information in the box labelled B indicates that the gene is not sex-linked.
if it was sex-linked it would be on the x chromosome;
males would pass the allele to their daughter;
The pedigree chart shows the incidence of hemophilia in some of the descendants of Queen
Victoria; State the probability that Edward had hemophilia
0.5/50 %;
Explain the reasons for none of the females in the pedigree chart having hemophilia.
hemophilia is X-linked/sex-linked/carried on the X chromosome; females have two X chromosomes
females would require the allele on both X chromosomes to have the disease
females can be carriers when allele is only on one chromosome;
Identify the genotype of the male wire-haired dog.
WwKk
Outline the inheritance of blood types in the ABO blood system in humans.
IA is dominant and i is recessive / IB is dominant and i is recessive
c. Group O (only) with ii and Group A with IAi or IAIA / Group B with IBi or IBIB
d. IA and IB are co-dominant so Group AB with IAIB
one allele/copy of the gene inherited from each parent/Punnett square showing this