Where new gene combinations come from
Grade 9 Science Worksheet
Circle the best answer.
“Chromosome cards (model, not to scale). One cell with 2 sets of chromosomes; pair 1 is shown. Before the crossover,” Ari follows a pair with genes A and B. The dark chromosome has A B and the light one has a b. One crossover happens between the genes. Which list shows the four chromatids afterward?
- A b, A b, a B, a B
- A B, A B, a b, a b
- A B, A b, a b, a b
- A B, A b, a B, a b
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Chromosome cards (model, not to scale). One cell with 2 sets of chromosomes; each chromosome has 2 chromatids. Pair 1: a dark chromosome with alleles A and B and a light chromosome with alleles a and b. Pair 2: a dark chromosome with allele C and a light chromosome with allele c. The cell is early in meiosis, with each pair lying side by side.
Esme looks at a cell with 2 pairs of chromosomes. Genes A and B are on pair 1, and gene C is on pair 2. Which chromatids can swap pieces in crossing over?
- The two sister chromatids of one chromosome, in prophase I
- A dark and a light chromatid of pair 1, in prophase II
- A dark and a light chromatid of pair 1, in prophase I
- A dark chromatid of pair 1 and a light chromatid of pair 2, in prophase I
Pea plant fact card
item value pairs of chromosomes 7 ways each pair can line up 2 Jun reads that a pea plant has 7 pairs of chromosomes. How many line-ups can the 7 pairs make at the middle, before crossing over?
- 2 line-ups
- 128 line-ups
- 14 line-ups
- 49 line-ups
Model cell card
item value line-ups at the middle 64 ways each pair can line up 2 A model cell can line up its chromosomes in 64 different ways at the middle. Kira wants the number of pairs. How many pairs does it have?
- 8 pairs
- 32 pairs
- 64 pairs
- 6 pairs
Two parents (model data)
item value pairs in each parent 3 kinds of gametes from each parent 8 Milo reads a card for two parents. Each can make 8 kinds of gametes by independent assortment alone. How many offspring combinations can random fertilization give?
- 16 combinations
- 8 combinations
- 24 combinations
- 64 combinations
Offspring combinations from two parents (model data)
pairs in each parent kinds from each parent offspring combinations 2 4 16 3 8 64 4 16 ? Noah reads how many offspring combinations two parents can make. Both parents have the same number of pairs. What belongs in the blank for 4 pairs?
- 128
- 112
- 256
- 16
Two human parents (arithmetic)
item value pairs in each parent 23 line-ups for each parent 8,388,608 line-ups for the two parents together ? Pia reads the arithmetic for two parents with 23 pairs each. Which statement gives the count for combined line-ups after random fertilization?
- 1, since each parent passes on one fixed set of chromosomes to the offspring
- 2²³ + 2²³ = 2²⁴, about 16.8 million, since the two parents' line-ups form one longer list
- 2²³ × 2²³ = 2⁴⁶, about 70 trillion, since any line-up from one parent can meet any from the other
- 2²³, about 8.4 million, since just one parent's line-ups count for the offspring
Ren watches model cell X. Its 3 pairs line up at the middle, and each pair faces a random pole. Which source of variation is this?
- Random fertilization, the joining of two gametes
- Crossing over, the swap of pieces in prophase I
- Mutation, a change in the DNA of a gene
- Independent assortment, the random line-up of pairs
Chromatid card (model)
item value top allele on this chromatid H bottom allele on this chromatid j alleles on the dark chromosome H and J alleles on the light chromosome h and j Tala finds a chromatid with allele H from the dark chromosome and allele j from the light one. Which process made it, and what does that process make?
- Independent assortment: whole chromosomes in new mixes, in metaphase I
- Crossing over: chromatids that mix both homologs, in prophase II
- Crossing over: chromatids that mix both homologs, in prophase I
- Crossing over: chromatids with brand-new alleles, in prophase I
Four sources of variation (model)
source what it does crossing over swaps pieces between non-sister chromatids independent assortment lines up pairs at random random fertilization joins one gamete with another mutation changes the DNA sequence of a gene A model plant has a flower-color allele that neither parent had. Which source of variation is the ultimate source of new alleles, asks Zee?
- Independent assortment, because pairs mix into new alleles
- Random fertilization, because joining cells build new alleles
- Crossing over, because swapped pieces form new alleles
- Mutation, a change in the DNA sequence of a gene
