Where new gene combinations come from

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Chromosome cards (model, not to scale). Crossing over between D and E happens in some cells but not in others. Bo deals a parent cell with D and E on pair 1 and F on pair 2. Crossing over between D and E happens in some cells. How many gamete types are possible?

   • 8 gamete types
   • 16 gamete types
   • 6 gamete types
   • 4 gamete types

2. Read this first

   Use this

   Chromosome cards (model, not to scale). Parent 1 cell has 2 sets of chromosomes and 2 pairs. Pair 1: a dark chromosome with allele K and a light chromosome with allele k. Pair 2: a dark chromosome with allele M and a light chromosome with allele m. Each pair lines up on its own. Grid: the side edge for parent 2 is already dealt: K m, k m. The top edge for parent 1 is ?.

3. 2.

   Esme deals pair cards to the edge of a grid. Genes K and M are on different pairs of parent 1. Which choice lists parent 1's gamete types for the top edge?

   • K M, K m, k M, k m
   • K M, k m
   • K k, M m
   • K M, K m, k m

4. Fruit fly test cross card (Morgan, 1912; the total is model data)

   item	value
   genes	body color and wing length
   recombination frequency	17 percent
   offspring in the model total	1,000

5. 3.

   Jun reads that Morgan's fruit flies gave a recombination frequency of 17 percent for body color and wing length. About how many of 1,000 test cross offspring are recombinant?

   • About 500
   • About 170
   • About 830
   • About 17

6. Model test cross counts (model data)

   group	offspring
   parental types	880
   recombinant types	120
   total	1,000

7. 4.

   Kira counts a model test cross: 880 offspring look like a parent, and 120 show a new combination. What is the recombination frequency?

   • 13.6 percent
   • 12 percent
   • 88 percent
   • 50 percent

8. Recombination frequencies for genes P, Q and R on one chromosome (model data)

   gene pair	frequency
   P and Q	4 percent
   Q and R	9 percent
   P and R	13 percent

9. 5.

   Luz reads recombination frequencies for genes P, Q and R on one chromosome. Map distances add up. Which gene lies in the middle?

   • R, since P and R have the largest value, 13 percent
   • Q, since 4 + 9 = 13 matches the P to R distance
   • No gene can be found, since percentages do not add
   • P, since P and Q have the smallest value, 4 percent

10. Notebook on crossing over

    line	what the notebook says
    1	Before meiosis, each chromosome is copied into 2 sister chromatids
    2	In prophase I, homologous chromosomes pair up gene for gene
    3	Crossing over swaps pieces in prophase I and again in prophase II
    4	The swaps make recombinant chromatids with new allele combinations

11. 6.

    Milo's notebook is about crossing over. One line is wrong. Which fix is right?

    • Line 2 should say sister chromatids pair up and swap pieces with each other
    • Line 1 should say the chromosomes are copied again before meiosis II
    • Line 4 should say the swaps make brand-new alleles in each chromatid
    • Line 3 should say crossing over happens in prophase I, not prophase II

12. Notebook on a pair of chromosomes

    line	what the notebook says
    1	Each chromosome was copied before meiosis, so it has 2 sister chromatids
    2	In prophase I, the dark and light chromosomes of a pair lie side by side
    3	The 2 sister chromatids of the dark chromosome swap pieces with each other
    4	The swap happens in prophase I, before the pairs line up at the middle

13. 7.

    Pia's notebook is about a swap of pieces in a pair. One line is wrong. Which fix is right?

    • Line 1 should say the copying happens after the pairs line up at the middle
    • Line 2 should say the dark and light chromosomes are identical copies
    • Line 3 should say a dark chromatid swaps pieces with a light chromatid
    • Line 4 should say the swap happens in prophase II, after the cells divide

14. Claim card (model)

    item	value
    claim	gametes made by different cells of one parent can differ even when no crossing over happens
    pairs in each parent cell	3
    chromosomes in each pair	a dark one and a light one

15. 8.

    Ren claims that gametes made by different cells of one parent can differ even when no crossing over happens. Which claim and reason are right?

    • True, since each pair lines up at random, so gametes get different mixes of dark and light chromosomes
    • False, since crossing over is the one way that gametes from different cells can differ
    • False, since the dark chromosomes travel to one gamete together and the light ones to another
    • True, since sister chromatids swap pieces before the pairs line up at the middle
16. 9.

    Tala compares two groups. Group X makes offspring by budding, which gives copies. Group Y uses meiosis and fertilization. Which claim about variation for natural selection is right?

    • Group Y offers more, since crossing over makes new alleles that neither parent had
    • Group Y offers more, since crossing over happens in both meiosis I and meiosis II
    • Group Y offers more, since crossing over, assortment and fertilization make new allele combinations
    • The groups offer equal variation, since mutation is the source of variation in each group
17. 10.

    Zee claims that if a crossover happens between two linked genes in every meiosis, all offspring of a test cross show new combinations. Which reply is right?

    • True, since sister chromatids swap too, so the 4 chromatids change
    • False, since 25 percent is the most that crossing over can give for two genes
    • False, since crossing over cannot happen between genes on the same chromosome
    • False, since a crossover changes 2 of the 4 chromatids, so about 50 percent of offspring are recombinant