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Biology Ch. 6
Terms in this set (34)
In the XO sex-determination system, what happens when the male passes on a sex chromosome?
If the male passes on his only X, then the offspring will be XX—and will always be female.
In the XY system of sex determinism, if a sperm cell with a Y chromosome fertilizes an egg cell, which of the following is true?
There is a 100 percent chance the offspring will be male because the Y from the sperm will combine with the X from the egg to create a cell that is XY, which is male. XX is female.
What are the phenotypic possibilities of a cross between a colorblind mother and a normal father?
All of their male offspring will be colorblind. Their female offspring will not be colorblind.
How is balding an example of a sex-influenced trait?
Balding is an example of a sex-influenced trait because if a male is heterozygous for the balding trait, he will exhibit balding; but a female having the heterozygous genotype will not. So, with sex-influenced traits, the gender will affect whether or not the trait is expressed.
Why are more males than females affected by sex-linked recessive diseases?
More males are affected by sex-linked recessive diseases than females, because men only have one X chromosome. If they get only one recessive allele, they will be afflicted with the disease. Because females have two X chromosomes, having only one recessive allele will not give them the disorder. Both alleles would have to be recessive.
What does a person with hemophilia lack?
People with hemophilia lack a protein that helps their blood to clot.
What does it mean for a disorder to be sex-linked?
A sex-linked disorder means that the genes coding for that trait are found on the X chromosome.
What does it mean for a trait to be sex-influenced?
Sex-influenced traits will express themselves differently depending on the sex of the individual.
How is prostate cancer an example of a sex-limited trait?
Prostate cancer is an example because only males have a prostate and are therefore the only ones that can get prostate cancer.
What are the genotypic possibilities of a cross between a mother who is a carrier for hemophilia and a father who is hemophilic?
The possible genotypes are XHXh, XhXh, XHY, XhY.
What does it mean for a trait to be sex-limited?
When a trait is sex-limited, it means that it only occurs in traits unique to one sex or the other. Both a man and a woman may have the gene that codes for ovarian cancer, but only the woman will get it.
When can nondisjunction occur?
Nondisjunction can occur during the first or second meiotic division.
Name four examples of nondisjunction disorders, and explain how the chromosomes of people afflicted with these disorders are different from normal chromosomes.
Trisomy 21, called Down syndrome, has an extra chromosome 21.
Trisomy 18, called Edwards syndrome, has an extra chromosome 18.
Trisomy 13, called Patau syndrome, has an extra chromosome 13.
Turners syndrome has only one X for the sex chromosome—missing a sex chromosome.
Klienfelters Syndrome has XXY for sex chromosomes—has one extra sex chromosome.
Explain the difference in nondisjunctional gametes for each stage at which nondisjunction can occur.
If nondisjunction occurs at the first stage, then all the gametes will be affected. Typically, this means that two of the gametes will have one extra chromosome, and the other two gametes that are created will have one less chromosome than normal. If the nondisjunction occurs during the second division in one of the cells, then there will be two gametes that are normal, one gamete that has one extra chromosome, and one gamete that is missing a chromosome.
Nondisjunction is the unequal division of chromosomes during meiosis.
What is the probability of a type BO mother and a type AO father having a type O child?
Briefly describe Mendel's two laws.
Mendel's first law is the law of segregation. This law states that the alleles for a trait will separate during formation of gametes and each gamete will only have one allele. Mendel's second law is the law of independent assortment. This law states that alleles from different genes will assort independently from one another during gamete formation.
Describe what happens during crossing over.
During crossing over, homologous chromosomes exchange genetic material, thus mixing up the combinations of traaits
When does the law of independent assortment not work?
The law of independent assortment does not work when the two genes in question are located close together on the same chromosome.
How can you tell when genes are linked?
You can tell when genes are linked when the offspring show more parental types for two different traits than there are recombinants.
Which of the following offspring have recombinant gene types for YyRr and yyrr parents?
Which of the following do humans have?
23 pairs of chromosomes, of which 1 pair are sex chromosomes XXX
1 pair of sex chromosomes and 23 pairs of autosomes
1 pair of sex chromosomes and 12 pairs of autosomes
22 pairs of sex chromosomes and 1 pair of autosomes
What organism has ZZ sex chromosomes?
Which of the following is a description of Klinefelter's syndrome?
low IQ, only afflicts males, and an extra sex chromosome (XXY)
Which of the following statements about sex-linked disorders is true?
It's easier for women to express a sex-linked disorder.
Trisomy 21 is a good example of a sex-linked disorder.
It's easier for men to express a sex-linked disorder. XX
Balding is a good example of a sex-linked disorder.
Which of the following is the definition of sex-influenced?
that trait expression in heterozygotes is determined by the carrier's sex
Which of the following is a sex-linked trait?
Prostate cancer is a sex-limited trait. Please review objective 2 for more help with this concept.
When do genes show "linkage"?
when they are close together on the same chromosome
What are genes found on the X chromosome considered?
When using a pedigree, females are drawn as what shape?
If a red blood cell has no A or B proteins on it but does have Rh proteins, what blood type is the red blood cell?
What is another name for Patau syndrome?
Which sex chromosomes do a person with Turner's syndrome have?
Which of the following traits is a good example of a trait with multiple alleles?
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