Worksheet: Genetic Diagrams

In this worksheet, we will practice using genetic diagrams to make predictions about genotypes and phenotypes.

Q1:

A heterozygous black cat (Bb) reproduces with a homozygous recessive brown cat (bb).

Which Punnett square shows the correct cross?

  • A
    B b
    B BB Bb
    b Bb bb
  • B
    B b
    b Bb Bb
    b bb bb
  • C
    B b
    b Bb bb
    b Bb bb
  • D
    B B
    b Bb Bb
    b Bb Bb

Q2:

Sex in humans is determined by two chromosomes, X and Y. What is the correct combination of chromosomes for males and females from the given choices?

  • AXX = male, XY = female
  • BXY = male, XX = female

Q3:

Which of the following Punnett squares correctly outlines how sex is determined in humans?

  • A
    Gametes X X
    X XX XY
    X XX XY
  • B
    Gametes X Y
    X X Y
    X X Y
  • C
    Gametes X Y
    X XX XX
    X XY XY
  • D
    Gametes X Y
    X XX XY
    X XX XY

Q4:

The allele for orange fur in tigers is dominant (T).

What is the genotype of a tiger homozygous dominant for orange fur?

  • ATt
  • BTT
  • Ctt

What is the genotype of a tiger heterozygous for orange fur?

  • Att
  • BTt
  • CTT

What is the probability that a homozygous dominant male and a heterozygous female will produce offspring with orange fur?

Q5:

The allele for freckles in humans is dominant (F). What is the probability that a couple who are both heterozygous for the allele will have a child with freckles? Use a Punnett square to help you.

Q6:

What is the probability that a pregnancy will produce a female offspring?

Q7:

A plant homozygous dominant for red flowers (RR) reproduces with a plant homozygous recessive for white flowers (rr).

Which Punnett square shows the correct cross?

  • A
    R R
    R RR RR
    r Rr Rr
  • B
    R R
    r Rr RR
    r Rr RR
  • C
    R R
    r Rr Rr
    r Rr Rr
  • D
    r r
    r Rr Rr
    r Rr Rr

What percentage of the offspring will have white flowers?

Q8:

Give the correct combination of alleles to complete the Punnett square provided.

G G
1 GG GG
2 Gg Gg
  • A1 = g, 2 = G
  • B1 = G, 2 = G
  • C1 = G, 2 = g
  • D1 = g, 2 = g

Q9:

The allele for having a straight hairline (h) is recessive to the allele for having a widow’s peak (H). A couple, both heterozygous for this trait, are having a child.

What is the probability that the child will have a straight hairline?

What is the probability that the child will be a carrier for the straight hairline allele?

What is the probability that the child will be homozygous dominant?

Q10:

Give the correct combination of alleles to complete the Punnett square provided.

A 2
1 AA Aa
a Aa aa
  • A1 = a, 2 = A
  • B1 = A, 2 = a
  • C1 = a, 2 = a
  • D1 = A, 2 = A

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