Chapter 12 Flashcards Flashcards by Kennedy Bluford

The human body contains __ chromosomes that come in __ homologous pairs

46
23

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Two examples of diseases inherited on the x chromsome

color blindness
hemophilia

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Is baldness caused by a recessive or dominant allele?

recessive

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Sex-linked traits are said to _____ a generation

skip

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Meiosis is responsible for producing _____ ________ cells from one original cell

four
haploid

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failure of chromosomes to separate from each other during either round of meiosis; can occur in either meiosis or mitosis in either sex

Nondisjunction

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Nondisjunction is responsible for syndromes such as

turner syndrome
down syndrome

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Four genes (A, B, C, and D) are on the same chromosome. The recombination frequencies are as follows: A-B: 19%; B-C: 14%; A-C: 5%; B-D: 2%; A-D: 21%; C-D: 16%. Based on this information, which sequence of genes is correct?

ACBD

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A linkage map __________.

orders genes on a chromosome based on recombination frequencies

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A 1:1:1:1 ratio of offspring from a dihybrid testcross indicates that ___________.

the genes are not linked or are more than 50 map units apart

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The chromosome theory of inheritance states that __________.

genes occupy specific positions on chromosomes, homologous chromosomes segregate from each other during meiosis, and chromosomes assort independently during meiosis

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A wild type is ___________.

the phenotype found most commonly in nature

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When a person has Down syndrome, he or she has an extra chromosome 21. Therefore, Down syndrome is a kind of __________ and results from __________.

aneuploidy; nondisjunction of chromosome 21 during meiosis I

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The recombination frequency between two gene loci __________.

increases as the distance between the two loci increases

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Why did Thomas Hunt Morgan choose Drosophila for his genetics experiments?

A single mating can produce many offspring, and Drosophila chromosomes can be easily distinguishable under a light microscope.

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In which of the following structures would you expect to find a Barr body?

a liver cell of a woman

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Which of the following is the only known viable human monosomy?

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A genetic defect in humans results in the absence of sweat glands in the skin. Some men have this defect all over their bodies, but in women it is usually expressed in a peculiar way: A woman with this defect typically has small patches of skin with sweat glands and other patches without sweat glands. In women, the pattern of sweat-gland distribution can best be explained by __________.

X chromosome inactivation

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The chromosomal abnormality in which a fragment of a chromosome breaks off and then reattaches to the original chromosome in the same place but in the reverse direction is called __________.

inversion

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During meiosis, homologous chromosomes sometimes “stick together” and do not separate properly. This phenomenon is known as __________.

nondisjunction

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Which of the following results of Thomas Hunt Morgan’s experiments with white-eyed mutant flies was unexpected in light of Mendelian genetics?

Among the F2 progeny, only males had white eyes. All of the females had red eyes.

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Gene A is normally found on chromosome number 15 in humans. If amniocentesis reveals fetal cells containing gene A on chromosome 17, but not on 15, the best explanation would be that __________.

translocation occurred

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A woman is red-green color-blind. What can we conclude, if anything, about her father?

Her father is red-green color-blind.

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In an X-linked, or sex-linked, trait, it is the contribution of __________ that determines whether a son will display the trait.

the mother

Queen Victoria was a carrier of a recessive sex-linked allele for hemophilia. Which of the following possibilities could explain the presence of the hemophilia allele in her genotype?

Either her mother was a carrier or her father had hemophilia.

Which of the following best describes the function of the XIST gene in X chromosome inactivation?

The XIST gene on the X chromosome to be inactivated is expressed to produce multiple RNA molecules that bind to that same chromosome and effectively cover it up.

Duchenne muscular dystrophy is caused by a sex-linked recessive allele. Its victims are almost invariably boys, who usually die before the age of 20. Why is this disorder almost never seen in girls?

To express an X-linked recessive allele, a female must have two copies of the allele.

Individuals with an extra X chromosome __________.

may have subnormal intelligence or be at risk for learning disabilities

In werewolves, pointy ears (P) are dominant over round ears (p). The gene is on the X chromosome. (Sex determination in werewolves is the same as for other humans.) A certain female werewolf has pointy ears even though her father had round ears. What percentage of her sons will have round ears if she mates with a werewolf with round ears?

50%

Hemophilia is a sex-linked disorder. The daughter of a father with hemophilia and a carrier mother has a __________ probability of having hemophilia.

50%

X-linked genes differ from Y-linked genes in which of the following ways?

Sons and daughters have equal probabilities in inheriting a recessive allele of an X-linked gene from their mother, but only sons can inherit rare Y-linked genetic disorders from their father.

Modes of Inheritance

autosomal x-linked

Autosomal modes of inheritance are either

recessive or dominant

albinism cystic fibrosis phenylketonuria (PKU) sickle cell disease tay sachs disease

Examples of diseases caused by autosomal recessive inheritance

achondroplasia huntington's disease

Examples of diseases caused by autosomal dominant inheritance

X-linked inheritance is

recessive

red-green color blindness duchenne muscular dystrophy hemophilia

Examples of diseases caused my x-linked inheritance

Carriers

individuals heterozygous for recessive disorder

Affected

individuals with condition/ disorder

Hemizygous

individuals who only have one copy of a gene

Carriers can be either males or females two carrier parents can have affected offspring both males and females can be affected

Autosomal Recessive

True or False: two parents affected with autosomal recessive disorder can have unaffected children

false

carriers are not possible tends to show up in every generation both males and females can be affected

Autosomal Dominant

True or False: children affected with an autosomal dominant disorder must have an affected parent

true

carriers are only female unaffected carrier females can have affected sons affected females must have an affected father and mother who is at least a carrier males are hemizygous

X-linked

True or False: men are more likely to be affected with the x-linked recessive trait

true

Genes are said to be ________ when they are located close on the same chromosome and are inherited together

linked

Alleles of linked genes can be recombined by

recombination

If two genes on a chromosome are close together, it is ______ likely that they will recombine

less

Recombinant offspring have _________ phenotypes as parent

different

Parental-type offspring have the ______ phenotypes as parent

same

As the distance between genes increases on a chromosome, the chances of crossing over is _____ likely leading to a ______ recombination frequency

less higher

Sex determination system in grasshoppers

the X0 system female: xx male: X0

Sex determination system in chickens

the ZW system female: ZW male: ZZ 22 pairs of chromosomes

Sex determination system in bees

the haplo-diploid system female: diploid male: haploid female has 32 pairs of chromosomes male has 16 pairs of chromosomes

a condensed inactive x chromosome

Barr Body

X activation ____ random in homologous chromosomes

What doesn't separate in nondisjunction meiosis 1?

homologs

What doesn't separate in nondisjunction in meiosis 2?

sister chromatids

Resulting gametes from Nondisjunction in Meiosis 1

0 normal gametes 4 abnormal gametes

Resulting gametes from Nondisjunction in Meiosis 2

2 normal gametes 2 abnormal gametes

Nondisjunction in ________ can result in gametes with the correct number of chromosomes

meiosis 2

Which syndrome is characterized by the XO chromosome abnormality?

Turner syndrome

What kind of cell results when a diploid and a haploid gamete fuse during fertilization?

a triploid cell

Of the following chromosomal abnormalities, which type is most likely to be viable in humans?

trisomy

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.

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.

Chromosome behavior at Metaphase 1 of Meiosis

two chromosome arrangements equally probable at metaphase plate

Chromosome behavior at Anaphase 1 of Meiosis

homologous chromosomes separate

Chromosome behavior at Telophase 2 of Meiosis

sister chromatids have separated

Chromosome behavior during fertilization of Meiosis

chromosomes in haploid gametes combine in diploid zygote

Nondisjunction Event: meiosis occurs normally Number of chromosomes in gametes:

3 only

Nondisjunction event: nondisjunction of one chromosome pair in meiosis 1 Number of chromosomes in gametes:

2 or 4

Nondisjunction event: nondisjunction of all three chromosome pairs in meiosis 1 Number of chromosomes in gametes:

0 or 6

Nondisjunction event: nondisjunction of one chromosome in one daughter cell in meiosis 2 Number of chromosomes in gametes:

2, 3 or 4

Victoria Queen of England had several children, including those shown on the pedigree. Which of Victoria's children inherited the hemophilia allele from her?

Leopold Duke of Albany Alice Princess of Hesse Beatrice Princess of Battenburg

Nondisjunction event: nondisjunction of all three chromosomes in one daughter cell in meiosis 2 Number of chromosomes in gametes:

0,3, or 6