Crossing-over and Recombination
Two homologous chromosomes exchange matching DNA segments. What is this process called?
What is crossing-over?
The random orientation of homologous pairs during metaphase I produces this source of genetic variation.
What is independent assortment?
Name one of the three major sources of genetic variability in sexual reproduction.
What is crossing-over, independent assortment, or random fertilization?
In animals, meiosis takes place in reproductive organs and produces these cells.
What are gametes, like sperm and eggs?
Two haploid gametes fuse during sexual reproduction. What is the resulting cell called?
What is a zygote?
Crossing-over occurs between these two types of chromatids, rather than between sister chromatids.
What are nonsister chromatids?
In a species with three chromosome pairs, how many different combinations of maternal and paternal chromosomes can a gamete receive through independent assortment alone?
What is 23 = 8 combinations?
A species has six chromosome pairs. Ignoring crossing-over, how many chromosome combinations can its gametes have?
What is 26 = 64 combinations?
In plants, meiosis produces haploid spores that grow by mitosis into this generation.
What is the gametophyte generation?
Two siblings have the same biological parents but different chromosome combinations. What helps explain this difference?
What is independent assortment, crossing-over, and random fertilization?
A chromosome now contains a new combination of alleles from its homolog. What type of chromosome is it?
What is a recombinant chromosome?
A cell has four homologous chromosome pairs. Ignoring crossing-over, calculate the number of possible chromosome combinations in its gametes.
What is 24 = 16 combinations?
Two children receive different combinations of maternal and paternal chromosomes from the same parents. Which meiotic process helps make this possible?
What is independent assortment?
Fertilization produces the diploid generation in plants. What is this generation called?
What is the sporophyte?
A plant spore grows into a multicellular organism through repeated mitotic divisions. Is that organism haploid or diploid?
What is haploid; the spore is haploid and mitosis maintains its chromosome number?
Assume one crossover occurs between two nonsister chromatids in a homologous pair of four chromatids. How many chromatids are recombinant immediately after that crossover?
What are two chromatids?
In humans, independent assortment alone allows this many possible chromosome combinations in a gamete.
What is 223 = 8,388,608 combinations?
Crossing-over creates new allele combinations within chromosomes, while independent assortment changes this.
What is the combinations of maternal and paternal chromosomes inherited together?
In some fungi and algae, the diploid stage lasts only this long before meiosis occurs.
What is the zygote stage; the diploid zygote undergoes meiosis?
In some fungi, gametes are produced by mitosis from a haploid individual. Why can the individual's gametes be genetically identical to one another?
What is mitosis copies the genome without the chromosome reshuffling associated with meiosis?
After one crossover between two nonsister chromatids, the four resulting chromatids include two unchanged chromatids and two with new allele combinations. What does this show about crossing-over?
What is it can produce both parental and recombinant chromosomes in the same meiotic division?
Two gametes each have 8 possible chromosome combinations. Assuming all combinations are equally likely and ignoring crossing-over, how many possible combinations can result when they unite?
What is 8 x 8 = 64 combinations in the resulting zygote?
A student claims that independent assortment is the only source of genetic variation in sexual reproduction. Name the two other sources they missed.
What is crossing-over and the random union of male and female gametes?
Unlike animals, most plants do not produce gametes directly by meiosis. Trace the sequence from a plant's diploid generation to its gametes.
What is sporophyte → meiosis → haploid spores → mitosis → gametophyte → gametes?
A student says, “Meiosis always produces gametes directly.” Use the life cycles of plants and some fungi or algae to explain why this is incorrect.
What is in most plants, meiosis produces spores that grow into gametophytes, which then produce gametes. In some fungi and algae, meiosis produces haploid spores or cells, and gametes can form later through mitosis or differentiation?