Monozygotic (identical) twins arise when a single egg, fertilized by a single sperm, divides early in development, giving rise to two genetically identical embryos. A recent study examined a pair of monozygotic twins in which one of the twins had trisomy 21 and the other twin had two normal copies of chromosome 21. Explain how two identical twins could differ in their number of chromosomes

Monozygotic (identical) twins arise when a single egg, fertilized by a single sperm, divides early in development, giving rise to two genetically identical embryos. A recent study examined a pair of monozygotic twins in which one of the twins had trisomy 21 and the other twin had two normal copies of chromosome 21. Explain how two identical twins could differ in their number of chromosomes

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Description: Monozygotic (identical) twins arise when a single egg, fertilized by a single sperm, divides early in development, giving rise to two genetically identical embryos. A recent study examined a pair of monozygotic twins in which one of the twins had tri

Human Biology (MindTap Course List)

11th Edition

ISBN:9781305112100

Author:Cecie Starr, Beverly McMillan

Publisher:Cecie Starr, Beverly McMillan

Chapter20: Chromosomes And Human Genetics

Section: Chapter Questions

Problem 3CT: People with Down syndrome have an extra copy of chromosome 21, for a total of 47 chromosomes....

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People with Down syndrome have an extra copy of chromosome 21, for a total of 47 chromosomes. However, in a few cases of Down syndrome, 46 chromosomes are present. This total includes two normal-looking chromosomes 21, one normal chromosome 14, and a longer-than-normal chromosome 14. Interpret this observation. How can these individuals have 46 chromosomes?
Variations in Chromosome NumberAneuploidy Describe the process of nondisjunction and explain when it takes place during cell division.
A phenotypically normal boy has 45 chromosomes, but his sister, who has Down syndrome, has 46. Suggest an explanation that explains both children.
During meiosis, when crossing-over occurs between two homologous chromosomes, it does not happen at a single point, but rather two points with a stretch of DNA in between. What are the two junction points called?What is the region between the two points called and what is different about this region compared to how double-stranded DNA usually is?If the region described in b.) is located within a gene and the two homologues have different alleles of this gene, what might happen that is a direct violation of Mendel’s first law? (Describe the process with 2-3 sentences of detail.)
Which statement about homologous chromosomes is FALSE? Select one: a. They contain the same genes in the same places along the length of the chromosome b. One member of the homologous pair came from your mother, the other from your father c. For a particular gene, one member of the pair may have one allele, while the other has a different allele d. They are joined together at the centromere as the two halves of the typical X-shaped chromosome
A meiotic-nondisjunction causes trisomy 8 in a newborn. If two of the three copies of chromosome 8 are identical, at what point during meiosis did nondisjunction take place? Explain how you arrived at this answer.
If an organism has 15 pairs of homologous chromosomes, how many chromosomes will each daughter cell have after telophase of mitosis? In this same organism, how many chromosomes will each daughter cell have after telophase II of meiosis?
. With regards to the grasshopper testes experiment, diakinesis is an ideal stage to determine chromosome number due to the degree of condensation of the chromosomes? Count the chromosomes at this stage. Does it represent a diploid or a haploid number?
Part C is actually 13 chromosomes in a cell of a pea plant that is monosomic for a single chromosome. How did my teacher get 13?
crossing over within a pericentric inversion produces chromosomes that have extra copies of some genes and no copies of other genes. The fertilization of gametes containing chromosomes with duplications or deletions often result in children with syndromes characterized by developmental delay, intellectual disability, abnormal development of organ systems, and early death. Maarit Jaarola and colleagues examined individual sperm cells of a male who was heterozygous for a pericentric inversion on chromosome 8 and determined that crossing over took place within the pericentric inversion in 26% of the meiotic divisions (M. Jaarola, R. H. Martin, and T. Ashley. 1998. American Journal of Human Genetics 63:218–224). Assume that you are a genetic counselor and that a couple seeks counseling from you. Both the man and the woman are phenotypically normal, but the woman is heterozygous for a pericentric inversion on chromosome 8. The man is karyotypically normal. What is the probability that this…
Consider a cell with 2 pairs of homologous chromosomes where Chromosome 1 with genes VWXYZ is the homolog of Chromosome 2 with genes vwxyz while Chromosome 3 with genes PQRST is the homolog of Chromosome 4 with genes parst. If a reciprocal translocation occurred between Chromosome 1 YZ genes and Chromosome 3 ST genes, give the following gamete types produced after meiosis: (Answer in Arabic numbers only) 1. Gamete/s with non-recombinant chromosomes 2. Gamete/s with 1 recombinant chromosome 3. Gamete/s with 2 recombinant chromosomes 4. Gamete/s with gene duplications 5. Gamete/s with gene deletions 6. Gamete/s with 2 normal chromosome sequences 7. Gamete/s with 1 normal chromosome sequence 8. Gamete/s with balanced translocation 9. Gametes/ with all dominant genes 10. Gamete/s with all recessive genes 11. Gamete/s with 10 different genes 12. Gamete/s with TSXWV genes 13. Gamete/s with vwxyz genes 14. Gamete/s with pqrst genes 15.Gamete/s with PORYZ
Consider a hypothetical DIPLOID organism with ONE PAIR of homologous chromosomes. How many DNA molecules are there per nucleus in a somatic cell in G1? 4 8 2 1 Picture 1 shows Bob’s chromosome #18 pair. Picture 2 shows Sue’s chromosome #18 pair. Bob and Sue have a stillborn son with three copies of chromosome #18 that look like picture 3. In which parent did the chromosome separation problem occur? Bob Sue Both parents You need additional information to determine which parent. Starting with a population of genetically identical mice, you discover two new independent mutant strains in which all of the animals have epileptic seizures. In both strains, you know that the epileptic seizures are due to a single DNA mutation. You cross a mutant mouse from one strain to a mutant mouse from the second strain and find that none of their many offspring undergo spontaneous seizures. From…