Where new gene combinations come from
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
A gamete gets 1 chromosome from each pair. No crossing over happens. Ari deals the chromosome cards of a parent cell. Pair 1 carries genes A and B, and pair 2 carries gene C. With no crossing over, which gamete could not be made?
- a b c, since a gamete cannot get three light alleles
- A B c, since a dark pair 1 chromosome cannot go with the light pair 2 chromosome
- a b C, since a light pair 1 chromosome cannot go with the dark pair 2 chromosome
- A b C, since A and b sit on different chromosomes of pair 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?
- 6 gamete types
- 4 gamete types
- 16 gamete types
- 8 gamete types
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 ?.
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 k, M m
- K M, K m, k M, k m
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 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 830
- About 500
- About 17
- About 170
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 Luz reads recombination frequencies for genes P, Q and R on one chromosome. Map distances add up. Which gene lies in the middle?
- P, since P and Q have the smallest value, 4 percent
- 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
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 Milo's notebook is about crossing over. One line is wrong. Which fix is right?
- Line 3 should say crossing over happens in prophase I, not prophase II
- Line 4 should say the swaps make brand-new alleles in each chromatid
- 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
Notebook on a cell with 8 pairs
line what the notebook says 1 Each pair can face either pole at the middle, in 2 ways 2 The pairs line up independently, so the choices multiply 3 With 8 pairs there are 2 × 8 = 16 line-ups 4 Crossing over adds more variety on top of this Noah's notebook is about a cell with 8 pairs of chromosomes. One line is wrong. Which fix is right?
- Line 2 should say the choices add up, one 2 for each of the 8 pairs
- Line 3 should multiply 2 eight times: 2⁸ = 256
- Line 1 should say each pair has 1 way, with the dark chromosomes on one side
- Line 4 should say crossing over adds new alleles on top of this
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 Pia's notebook is about a swap of pieces in a pair. One line is wrong. Which fix is right?
- 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
- Line 2 should say the dark and light chromosomes are identical copies
- Line 1 should say the copying happens after the pairs line up at the middle
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 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?
- 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
- False, since crossing over is the one way that gametes from different cells can differ
- True, since each pair lines up at random, so gametes get different mixes of dark and light chromosomes
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 crossing over cannot happen between genes on the same chromosome
- False, since 25 percent is the most that crossing over can give for two genes
- False, since a crossover changes 2 of the 4 chromatids, so about 50 percent of offspring are recombinant