Bio 283 Ch 8

Familial Down syndrome is similar to primary Down syndrome in that it is caused by trisomy 21. However, in familial Down syndrome, all or part of the third copy of chromosome 21 has translocated onto another autosome, typically chromosome 14. In cases of familial Down syndrome, one of the parents of the affected child is often a carrier of a translocated chromosome. The translocation carrier parent does not have Down syndrome because he or she has a total of two copies of chromosome 21. Suppose that a woman is a translocation carrier of chromosome 21 on chromosome 14. She conceives six zygotes with a normal man who carries no aneuploidies. Match the description of the chromosomes inherited by each zygote with the viability of the zygote. B. Viable with Downs Syndrome

1 Normal copy of Chromosome 14 + 2 normal copies of Chromosome 21 + 1 21 to 14 translocation

Familial Down syndrome is similar to primary Down syndrome in that it is caused by trisomy 21. However, in familial Down syndrome, all or part of the third copy of chromosome 21 has translocated onto another autosome, typically chromosome 14. In cases of familial Down syndrome, one of the parents of the affected child is often a carrier of a translocated chromosome. The translocation carrier parent does not have Down syndrome because he or she has a total of two copies of chromosome 21. Suppose that a woman is a translocation carrier of chromosome 21 on chromosome 14. She conceives six zygotes with a normal man who carries no aneuploidies. Match the description of the chromosomes inherited by each zygote with the viability of the zygote. C. Inviable

1 normal copy of 14 + 2 normal copies of 21, 1 normal copy of 21 + 2 normal copies of 14 and 1 normal copy of 21 + two normal copies of 14 + 1 21 to 14 translocation

In the fruit fly, Drosophila melanogaster, a known deletion on the X chromosome removes both a gene involved in the fly's development and the gene for eye color. The deletion is lethal when homozygous or hemizygous. Flies that are heterozygous for the mutation are viable, but have indentations at the wing margin. Therefore, the deletion is named the Notch mutation. The allele for wild type eyes is dominant over the allele for white eyes. Predict the phenotypic ratio of the offspring from a cross between a white-eyed notched female and a wild type male. -1 white-eyed notched female : 1 wild type female : 1 white-eyed notched male : 1 wild type male -1 wild type female : 1 notched female : 1 white-eyed male -1 white-eyed female : 1 notched female : 1 white-eyed male -1 wild type female : 1 notched female : 1 white-eyed male : 1 wild-typenotched male

1 wild type female : 1 notched female : 1 white-eyed male

Select the statements that explain why duplication is a driving force for evolution and the generation of new genes. 1. Genes duplicate and then diverge from the original sequence to create multigene families. 2. Phenotypic variations can occur when random fixed mutations are introduced into a new chromosomal environment. 3. Duplication of a gene segment always results in novel phenotypes. 4. Duplicated genes provide extra copies of DNA that are not constrained by an essential function.

1, 2 and 4

The Notch mutation is a deletion on the X chromosome of Drosophila melanogaster. Female flies heterozygous for Notch have an indentation on the margins of their wings. Notch is lethal in the homozygous and hemizygous conditions. The Notch deletion covers the region of the X chromosome that contains the locus for white eyes, an X-linked recessive trait. Determine the phenotypes and proportions of progeny produced by the cross. B. White Eyed Notch Female x Red Eyed Male

1/3 Red Eyed Notch Females, 1/3 Wild Type Females, 1/3 White Eyed Males

The Notch mutation is a deletion on the X chromosome of Drosophila melanogaster. Female flies heterozygous for Notch have an indentation on the margins of their wings. Notch is lethal in the homozygous and hemizygous conditions. The Notch deletion covers the region of the X chromosome that contains the locus for white eyes, an X-linked recessive trait. Determine the phenotypes and proportions of progeny produced by the cross. C. White Eyed Notch Female x White Eyed Male

1/3 White Eyed Females, 1/3 White Eyed Notch Females, 1/3 White Eyed Males

The Notch mutation is a deletion on the X chromosome of Drosophila melanogaster. Female flies heterozygous for Notch have an indentation on the margins of their wings. Notch is lethal in the homozygous and hemizygous conditions. The Notch deletion covers the region of the X chromosome that contains the locus for white eyes, an X-linked recessive trait. Determine the phenotypes and proportions of progeny produced by the cross. A. Red eyed Notch female x White Eyed Male

1/3 Wild Type Males, 1/3 Wild Type Females, 1/3 White Eyed Notch Females

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 these duplication or deficient chromosomes often results in children with syndromes characterized by developmental delay, mental retardation, abnormal development of organ systems, and early death. One study 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. Assume that a man and a 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 couple's child will inherit a duplicated or deficient chromosome 8 that results from crossing over within this pericentric inversion?

13 % Researchers determined that crossing over within this chromosome 8 pericentric inversion occurs in 26% of all meiotic events. When crossing over occurs during oogenesis in this heterozygous female, she will produce 50% recombinant and 50% nonrecombinant gametes. The probability of producing a gamete with a duplicated or deficient chromosome 8 is equal to the probability of crossing over within the pericentric conversion multiplied by the probability of inheriting a recombined chromosome.

Familial Down syndrome is similar to primary Down syndrome in that it is caused by trisomy 21. However, in familial Down syndrome, all or part of the third copy of chromosome 21 has translocated onto another autosome, typically chromosome 14. In cases of familial Down syndrome, one of the parents of the affected child is often a carrier of a translocated chromosome. The translocation carrier parent does not have Down syndrome because he or she has a total of two copies of chromosome 21. Suppose that a woman is a translocation carrier of chromosome 21 on chromosome 14. She conceives six zygotes with a normal man who carries no aneuploidies. Match the description of the chromosomes inherited by each zygote with the viability of the zygote. A. Viable normal or translocation carrier

2 normal copies of Chromosome 14 + 2 normal copies of Chromosome 21, 2 normal copies of Chromosome 14 + 1 normal copy of Chromosome 21 + 1 21 to 14 translocation

Which of the following statements describe mosaicism? 1. An arm wrestler's right-arm muscles are larger than those on his left. 2. A tortoiseshell cat has patches of orange and black fur. 3. A cancerous tumor develops in a woman's ovary. 4. The skin on a person's face and arms becomes much darker than the skin on the rest of the body after a summer of working outdoors. 5. A child with the phenotypic features characteristic of Down syndrome has a mixture of normal cells and cells with three copies of chromosome 21.

2,3 and 5

________ is a type of polyploidy that arises from the hybridization between two different species.

Allopolyploidy

Which of the following statements about chromosome inversions is correct? Chromosome inversions can reduce the number of chromosomes in a cell. Chromosome inversions lead to an increase in crossovers. Chromosome inversions do not affect gene expression. Chromosome inversions flip a segment of a chromosome 180 degrees.

Chromosome inversions flip a segment of a chromosome 180 degrees.

About 0.3% of human live births are trisomic. In contrast, only 0.02% of human live births are monosomic. Select the best explanation for why the occurrence of monosomics is less than that of trisomics. -Meiotic nondisjunction rarely produces monosomic gametes. -Mitosis is less likely to be completed correctly in monosomics than in trisomics. -Deleterious recessive alleles are always expressed on the monosomic chromosome but not on the trisomic chromosomes. -Gene dosage imbalance is more likely to lead to spontaneous abortion in monosomics than in trisomics.

Deleterious recessive alleles are always expressed on the monosomic chromosome but not on the trisomic chromosomes.

The spread of a complete metaphase chromosome set presented for diagnostic purposes is called a _____ (translocation, genome, karyotype, polyploidy)

Karyotype

Two brothers have X-linked red-green colorblind vision, and their parents have normal color vision. The first brother's karyotype is 47,XXY (Klinefelter syndrome), and the second brother's karyotype is 46,XY. In which parent and in what cell division phase did the first brother's chromosomal nondisjunction occur? Assume no recombination.

Meiosis II in the mother

Failure to separate for homologous chromosomes or sister chromatids is referred to as _______.

Nondisjunction

A man has a large inversion on one of his chromosomes. How might this impact his offspring? -No impact because all genetic information is retained -Minor genetic abnormalities due to minimal deficiency in genetic material -Fewer autosomes because normal synapsis during meiosis does not occur -Severe phenotypic abnormalities caused by unbalanced chromatids

Severe phenotypic abnormalities caused by unbalanced chromatids

Additional copies of a gene ___ (sometimes, always, never) cause cellular problems.

Sometimes

Match the definitions to the appropriate terms that describe the number of chromosomes. Four homologues of each chromosome

Tetraploid

Match the definitions to the appropriate terms that describe the number of chromosomes. Two extra copies of a specific chromosome

Tetrasomic

Which of the following statements about chromosome translocation is correct? Translocations only take place within a chromosome. Translocation and "crossing over" refer to the same phenomenon. Translocation can affect gene expression by moving a gene under the control of a different promoter. Translocations do not affect chromosome number.

Translocation can affect gene expression by moving a gene under the control of a different promoter.

Of all cases of primary Down syndrome, 92% is caused by _______.

Trisomy

Match the definitions to the appropriate terms that describe the number of chromosomes. A genome composed of four unique chromosomes

n=4