L19 Genetic Variation
When can nondisjunction occur? Choose the best answer.
In meiosis, when homologous chromosomes fail to separate In mitosis, when sister chromatids fail to separate In meiosis, when sister chromatids fail to separate
A researcher sequences a single DNA molecule from a sperm cell of an individual. She finds DNA sequences that were both maternally and paternally inherited by that individual. Which of the following processes could explain this result?
crossing over
Meiosis leads to genetic variation...
due to independent assortment of chromosomes +crossing over.
An advantage of asexual reproduction is that it _____.
enables the species to rapidly colonize habitats that are favorable to that species
Self fertilization (sperm and egg come from the same organism) leads to...
formation of progeny that is different from the parent
Meiosis result in...
four gametes with a chromosome composition different from that of the parent cells
sexual reproduction
fusion of gametes
Meiosis leads to...
generation of gametes and reduces chromosome number by half
Crossing over is a form of ......... that increases the genetic variability beyond that produced by random assortment of chromosomes
genetic recombination
What makes sexually reproduced offspring genetically different from their parents?
genetic recombination during meiosis
Meiosis leads to...
genetic variation in the gametes
clones
genetically identical to one another as well as to the parent
Independent distribution of chromosomes happens in...
meiosis I
Nondisjunction that leads to problems in offspring can occur in _____.
meiosis I and II
Nondisjunction that leads to problems in offspring can occur in:
meiosis I and II
Nondisjunction can happen in either...
meiosis I or meiosis II
Homologous pairs of chromosomes are lined up independently of other such pairs during _____.
metaphase I
Offspring that are genetically different from their parents are BLANK to survive and produce offspring if the environment changes
more likely
Crossing over produces...
new combinations of alleles on the same chromosome
What is the most common source of the extra chromosome 21 in an individual with Down syndrome?
nondisjunction in the mother
Crossing over, resulting in an increase in genetic variation, occurs between _____.
nonsister chromatids of homologous chromosomes
Offspring produced by sexual reproduction, the fusion of gametes, have a chromosome makeup different from...
one another and from that of either parent.
independent assortment of chromosomes is a result of _____.
the random way each pair of homologous chromosomes lines up at the metaphase plate during meiosis I
Aneuploid zygotes
those with too few or too many chromosomes
Aneuploid zygotes typically do not survive...
to produce viable offspring (miscarriages).
What kind of cell results when a diploid and a haploid gamete fuse during fertilization?
triploid cell
If nondisjunction occurs, two gametes will have an extra copy of a chromosome BLANK, and two gametes will lack that chromosome BLANK
trisomy ..... monosomy
Which syndrome is characterized by the XO chromosome abnormality?
turner syndrome
What is an outcome of genetic recombination?
the new combination of maternal and paternal chromosome segments that results when homologs cross over
Asexual reproduction results in greater reproductive success than does sexual reproduction when _____.
a species is in stable and favorable environments
A diploid organism whose somatic (nonsex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.
16
In human gamete production there is an average of _____ crossover events per chromosome pair.
2-3
Humans, with 46 chromosomes, can produce...
223 (~8.4 million) different combinations of chromosomes in gametes.
Normal human gametes carry _____ chromosomes.
23
If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred?
A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.
If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n − 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred?
A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.
What is a nondisjunction?
An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell
BLANK produces more offspring
Asexual reproduction
How would genetic variation be affected if maternal chromosomes always lined up on one side of the metaphase plate during meiosis I and paternal chromosomes always lined up on the other side?
Each gamete would inherit either all maternal or all paternal chromosomes.
Independent Assortment of Chromosomes Produces...
Genetic Variation
Of the following chromosomal abnormalities, which type is most likely to be viable in humans?
Trisomy
Based on the purifying selection hypothesis, how would changes in the rate of mutation influence whether sexual or asexual reproduction is favored?
Under high mutation rates, sexual reproduction is favored.
Sexual reproduction _____.
can produce diverse phenotypes that may enhance survival of a population in a changing environment
Outcrossing increases the genetic diversity of the offspring because...
chromosomes from two different parents are combined
Offspring produced during asexual reproduction are...
clones
Genetic variation results from...
independent assortment of chromosomes
Which processes lead to most genetic variation in sexually reproducing organisms?
independent assortment of chromosomes in meiosis, random fertilization, crossing over
Genetic diversity is essential for the health of a population to resist...
infectious diseases
In asexual reproduction, a damaged gene will be...
inherited by all of that individual's offspring
Which of the following would enable you to detect aneuploidy?
karyotyping
Sexually reproducing individuals are likely to have offspring that...
lack deleterious alleles present in the parent
Offspring that are genetically identical to their parents are BLANK to survive and produce offspring if the environment changes
less likely
Meiosis allows organisms to...
maintain the constant number of chromosomes from generation to generation
Human gametes are produced by _____.
meiosis
In many sexually reproducing species, gametes from different individuals combine to form offspring, a process called...
outcrossing
Diploid offspring contains...
pairs of homologous chromosomes
Natural selection against deleterious alleles is called...
purifying selection
Over time, purifying selection should steadily ........ the numerical advantage of asexual reproduction
reduce
Sexual reproduction can happen in a...
single organism
