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Ginkgo Copies and Axolotl Crosses at the Museum

Compare trees grown from cuttings with offspring from two parents.

Answer Key

Part 1: The ginkgo courtyard

Read the passage and Table 1, then answer the questions.

Living Things in the Fossil Hall

1The fossil hall at the Lakeshore Museum of Natural History ends at a glass wall that looks out on a courtyard of ginkgo trees. The museum, the people and the numbers here are made up, but they are based on real plants and animals. A fossil leaf beside the window looks almost exactly like the fan-shaped leaves outside. Fossil leaves like it are found in rocks more than 100 million years old. Sixth grader Javier Lund spent a week with the museum's curator of living collections, Dr. Bettina Oduya.

2Each ginkgo tree is either male or female. In fall, female trees drop seeds with a soft, very smelly coat, so many cities plant only male trees. Fifteen years ago, the museum planted 24 ginkgos in the courtyard, all in the same soil and sun. Twelve were grown from cuttings, small branches cut from one male tree that rooted in moist soil. The other twelve grew from seeds of a female tree in the city park. Wind had carried pollen to her from male trees nearby. Every fall, Dr. Oduya records the day each tree's leaves turn fully yellow. The seedling trees turned out to be a mix of males and females.

3Next to the fossils of early amphibians, the museum keeps a tank of living axolotls, salamanders from lakes near Mexico City. Most wild axolotls are dark. The museum also raises white axolotls with dark eyes. Skin color depends on one gene. The allele for dark skin (D) is dominant, and the allele for white skin (d) is recessive. Each pair's young hatch from eggs the female lays after the pair mates.

Table 1. The Courtyard Ginkgos After 15 Years
Trees grown fromTreesDay leaves turned yellowHeight (m)Male trees
Cuttings of one tree12Oct 28 to Oct 308.0 to 8.612
Seeds of one tree12Oct 18 to Nov 96.1 to 9.55
1.
Use Table 1. Find each span by subtracting the dates: for example, Oct 5 to Oct 9 is a span of 4 days.

The trees from cuttings turned yellow over a span of 2 days. The trees from seeds turned yellow over a span of 22 days.

2.
All 12 trees grown from cuttings are male. Which explanation fits the passage best?
  • A. The courtyard soil and sun made each young tree grow into a male tree.
  • B. Cuttings from a female tree rot before they root, so the gardeners lost those cuttings.
  • C. Pollen from the park's male trees reached the cuttings and made them male.
  • D. They grew from pieces of one male tree, so they carry that tree's genes.
3.
The trees grown from seeds varied much more in height and in the day their leaves turned yellow. Which explanation fits the passage best?
  • A. Each seed formed from pollen and an egg, so each seedling got a new mix of alleles.
  • B. Each seed got its genes from the female tree alone, but the seeds dried out unevenly.
  • C. The seedlings were younger, so they had not yet grown into copies of their mother.
  • D. The seedlings were planted in different soil, so each one grew in its own way.
4.
Why does it matter that all 24 trees grew in the same courtyard soil and sun?
  • A. The male trees then make seeds that drop into the courtyard each fall.
  • B. The trees then share pollen, so the cuttings slowly turn into seedlings.
  • C. Differences between the two groups then come mostly from their genes.
  • D. The trees in both groups then grow to the same height after 15 years.
5.
A city wants a row of ginkgos along a street that look alike, turn yellow together and never drop smelly seeds. Based on the passage and Table 1, which method fits these goals best?
  • A. Plant seeds from a female tree, since her seedlings grow more evenly in height
  • B. Root cuttings from one male tree, since the copies share its traits
  • C. Plant seeds from a male tree, since his seeds grow into male trees
  • D. Root cuttings from a female tree, since her copies turn yellow early
6.
Sort each statement by the kind of reproduction it describes.
A ginkgo branch roots in moist soil and grows into a tree.A ginkgo seed forms after wind carries pollen to a female tree.Twelve trees with identical genes turn yellow within 2 days of each other.A white axolotl hatches from an egg laid by a dark mother.Offspring get one allele for each gene from each parent.
Asexual (one parent)Sexual (two parents)
A ginkgo branch roots in moist soil and grows into a tree.
Twelve trees with identical genes turn yellow within 2 days of each other.
A ginkgo seed forms after wind carries pollen to a female tree.
A white axolotl hatches from an egg laid by a dark mother.
Offspring get one allele for each gene from each parent.

Part 2: The axolotl tank

Use paragraph 3 and Table 2. D = dark allele (dominant), d = white allele (recessive).

Table 2. Young From Three Axolotl Pairs
PairMotherFatherDark youngWhite young
1DarkDark18662
2WhiteDark10199
3WhiteWhite0150
7.
Both parents in Pair 1 are Dd. This Punnett square shows their cross. One box is missing.
Punnett Square: Pair 1
Mother ↓ / Father →Dd
DDDDd
dDd?

The missing box is dd. For each young of Pair 1, the chance of white skin is 25%.

8.

What percent of Pair 1's young in Table 2 were white? 25%

9.
Look at the three dark boxes in the Pair 1 Punnett square and how many of them are Dd.

Of Pair 1's 186 dark young, about how many would you expect to be Dd, carrying a hidden white allele? 124 young

10.
In Pair 2, the mother is white (dd). Which genotype does the dark father most likely have?
  • A. dd, because about half of the young came out white like the mother
  • B. Dd, because about half of the young were white, so he passed on d
  • C. DD, because a dark father passes a D allele to each of his young
  • D. DD, because more of the young were dark than white
11.
Dr. Oduya wants to know whether one dark young axolotl from Pair 1 is DD or Dd. When it grows up, which cross would tell her best?
  • A. Cross it with a white axolotl; any white young would show that it is Dd.
  • B. Cross it with a dark sibling; dark young would show that it is Dd.
  • C. Cross it with a DD axolotl; white young would show that it is Dd.
  • D. Raise it alone in a tank; a change to white skin would show that it is Dd.
12.
Javier says, "Cuttings and two-parent offspring are the same thing. Either way, the young are copies of a parent." Do you agree? Write a claim, give evidence from both tables, and explain your reasoning. Compare asexual and sexual reproduction in your answer.

Claim: I disagree. Cuttings make copies of one parent, but two-parent offspring get a new mix of alleles, so they vary. Evidence: The 12 ginkgos from cuttings of one male tree are all male, turned yellow within 2 days (Oct 28 to Oct 30) and are 8.0 to 8.6 m tall. The 12 trees from seeds include 5 males and 7 females, turned yellow over 22 days and range from 6.1 to 9.5 m. In the axolotls, two dark parents (Pair 1) had 186 dark and 62 white young, about 3 : 1, just as the Punnett square predicts. Reasoning: A cutting is asexual reproduction, so the new tree has the same genes as its one parent. In sexual reproduction each young gets one allele from each parent, so young of the same parents can differ, even showing a trait like white skin that neither parent shows.