Assuming that brown eyes is dominant to blue eyes in an auto

Assuming that brown eyes is dominant to blue eyes in an autosomal one gene simple dominance system, what proportion of the brown eyed offspring from a monohybrid cross (Bb times Bb) would be heterozygotes under each of the following conditions: no additional conditions, just normal Bb times Bb, the percentage of brown-eyed offspring that would be Bb ___________________ percentage of heterozygote brown eyed offspring if bb were lethal _______________ percentage of heterozygote brown eyed offspring if BB showed 25% reduced viability 4/9 _______________ percentage of heterozygote brown eyed offspring if b penetrates 33% in the heterozygote _______________________

Solution

In your first question, in a normal Bb xBb, the Bb population would be 50% as the ratio is 1:2:1.

Bb X Bb gives four alleles B, b, B, b which gives a population of BB, Bb, bB and bb, so 50% of the population would constitute Bb genotype.

the second part of the question, heterozygote offspring would be also 50% as Bb population is 50%. but if bb is found to be lethal, then the total population is distributed among BB and Bb, then it would constitute to 66.6%. this is because the ratio now would become 1:2 instead of 1:2:1.

third part of question, if BB showed 25% reduced viability which indicates among the 33% of BB individuals, 25% have to be reduced (25% of 33.33 is 8.33%) which shows that 25% (33.33-8.33=25)of the population is BB and remaining population which is 75% is the brown eyed heterozygote offspring.

forth part of the question, if 33% of b penetrates then they possess the phenotype of bb, this can have multiple answers

case1: if it is 1:2:1 ratio then 41.65% are bb if they are not lethal, 25% are BB and 33.35% are heterozygote brown eyed offspring.

case2: if it is 1:2 ratio i.e. if bb is lethal, so the population with heterozygotes would be 75% only

case3: if incomplete penetrance, then they do not exhibit the phenotype but carry the alleles which show that 25% have incomplete penetrance and 50% exhibit brown-eyed phenotype.

Hope it is clear!