They are asking about the evolutionary significance of going from asexual to sexual reproduction.
First, let's think about the differences between them.
Asexual reproduction means that the new individual is genetically identical to the parent; while in sexual reproduction there is a mix of genetic information from each parent.
Additionally, sexual reproduction involves the fusing of gametes, which are created through meiosis, where there is genetic recombination between homologous chromosomes, which gives more genetic variation.
Now let's look at the sentence:
In sexual reproduction independent 1. _____ and crossing over during 2._____ together with random 3.____ contribute to genetic variation in a population, which is the raw material for evolution by 4._______, especially in changing environment.
They are telling us that crossing over occurs in the process that we need to put in the second blank space, so as we know that crossing over happens during meiosis, we just have to pick between meiosis I and meiosis II. Crossing over happens during prophase I, so we should put meiosis I in the second blank space.
In sexual reproduction independent 1. _____ and crossing over during 2. meiosis I together with random 3.____ contribute to genetic variation in a population, which is the raw material for evolution by 4._______, especially in changing environment.
Now, we know that in space 1 they are asking for something that also occurs during meiosis I, and the other thing that happens during meiosis I is the assortment of chromosomes.
So, the sentence will be as follows:
In sexual reproduction independent 1. assortment of chromosomes and crossing over during 2. meiosis I together with random 3.____ contribute to genetic variation in a population, which is the raw material for evolution by 4._______, especially in changing environment.
Now we just have fertilization, natural selection, and mutations as options, because for blank 1 we choose between an assortment of chromosomes and assortment of chromatids, and for blank 2 we choose between mitosis, meiosis I, and meiosis II.
If we go back to the sentences, we see that space 3 asks for something that is random, and from the remaining options, only mutations can be random, which means mutations is the answer to space 3.
In sexual reproduction independent 1. assortment of chromosomes and crossing over during 2. meiosis I together with random 3. mutations contribute to genetic variation in a population, which is the raw material for evolution by 4._______, especially in changing environment.
Blank space 4 calls for a mechanism of evolution, and from all the terms, natural selection is the only mechanism of evolution.
This means the final sentence will be as follows:
In sexual reproduction independent 1. assortment of chromosomes and crossing over during 2. meiosis I together with random 3. mutations contribute to genetic variation in a population, which is the raw material for evolution by 4. natural selection, especially in changing environment.
