ESAT (Engineering and Science Admissions Test) · Biology

Inheritance

13 practice questions, each with the answer and an explanation.

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In pea plants, $A$ (tall) is dominant to $a$ (dwarf) and $B$ (purple) is dominant to $b$ (white). Two plants of genotype $A a B b$ are crossed. What is the probability of a dwarf, white offspring?
Blood group is controlled by alleles $I^{A}$ and $I^{B}$ (codominant) and $i$ (recessive). A mother of genotype $I^{A} i$ and a father of genotype $I^{B} i$ have a child. What is the probability the child has b…
Two unaffected parents have an affected child. What does this suggest about the condition?
A gene has two alleles. In a cross, the offspring show a $9 : 3 : 3 : 1$ phenotypic ratio. What does this ratio indicate?
A test cross of $AaBb\times aabb$ gives offspring in the ratio $42 A a B b : 8 A abb : 8 aa B b : 42 aabb$ . What is the recombination frequency between the two genes?
Allele frequencies in a population in Hardy-Weinberg equilibrium are $p = 0.7$ and $q = 0.3$ . In a population of $1000$ individuals, how many are expected to be heterozygous?
Two heterozygous parents ( $T t \times T t$ ) have a child. What is the probability that the child is homozygous recessive?
A tall pea plant of unknown genotype is crossed with a dwarf plant. Half of the offspring are tall and half are dwarf. What is the genotype of the tall parent?
Red-green colour blindness is caused by a recessive allele on the X chromosome. A carrier woman and an unaffected man have a son. What is the probability that the son is colour blind?
Two heterozygous parents ( $A a \times A a$ ) have three children. What is the probability that exactly one child is $aa$ ?
A cross is expected to give a $3 : 1$ ratio of tall to dwarf plants. Among $200$ offspring there are $160$ tall and $40$ dwarf. What is the value of $χ^{2}$ to $2$ decimal places?
In mice, a recessive allele $c$ at one gene stops pigment forming whatever alleles are present at a second gene for coat colour. A cross between two double heterozygotes gives an F2 ratio of $9$ agout…
Two unaffected parents already have one child with cystic fibrosis (a recessive condition). What is the probability that their next two children are both unaffected?

Inheritance

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