PLQ 16

Tay Sachs is a lysosomal storage disease that is inherited in an autosomal recessive manner. Individuals with Tay Sachs have a defect in the gene encoding hexosaminidase A, a lysosomal enzyme that breaks down cell membrane components called gangliosides. The inability to break down gangliosides causes harmful quantities of this lipid to accumulate in nerve cells of the brain, eventually leading to premature death of affected cells. There is no known cure for the disease, and death usually occurs by age 4. Jack and Jill have a child who has Tay-Sachs. What do you know about the genotypes of Jack and Jill? (T= dominant allele; t = recessive allele)offspring? Both are heterozygous Both are tt Its impossible to tell. Since both are adults, they do not have the disease. But, they could either be TT or Tt One is TT and the other is tt Both are TT

Both are heterozygous

Eyelash length is an inherited trait. In the human population, there is an eyelash length gene. There are two possible variants of this gene - an allele for long eyelashes (> 1cm) and an allele for short eyelashes (1 cm or less). How many eyelash length alleles does an individual have in one of her/his somatic cells? 1 3 23 46 2

2

A homologous pair of mitotic chromosomes will possess _______ alleles for each locus. Multiple Choice 1 8 50% of the 2 4

4

An organism that is heterozygous for two traits can produce a maximum of _______ different gametes for these traits. Multiple Choice 4; only if they are on different chromosomes 2; if they are on the same chromosome 2 4 8

4

A couple has five sons. What is the probability that their next child will be a girl? Multiple Choice 50% 0% 100% 25% 75%

50

What is the distribution of phenotypes from a cross of purple tall pea plants that are heterozygous for flower color and plant height? (Purple is dominant to white; tall is dominant to dwarf.) 63 purple tall; 28 purple tall; 27 white dwarf; 7 white dwarf 132 purple tall; 138 white dwarf 100% purple tall 54 purple tall; 6 white dwarf 27 purple dwarf; 28 purple tall; 31 white dwarf; 29 white tall

63 purple tall; 28 purple tall; 31 white dwarf; 29 white tall

What is a testcross? Any genetics cross you see on an exam A cross between two organisms of different species Any genetics cross you do in a lab or an abbey garden A cross between an organism of unknown genotype with a homozygous recessive individual A cross between two true-breeding individual (such as we see in the P generation)

A cross between an organism of unknown genotype with a homozygous recessive individual

Gregor Mendel: Check all that apply. carried out his experiments in an abbey garden. was a monk. conducted research that proved that the "blending hypothesis" was the correct explanation of how heredity worked. carried out his experiments on heredity by doing thousands of genetic crosses on a common garden plant. discovered the basic principles of hereditary.

All except "conducted research that proved that the "blending hypothesis" was the correct explanation of how heredity worked."

What is a dominant allele? An allele that totally beats up on a recessive allele An allele that will only have an affect on phenotype in a haploid organism; otherwise its presence will be masked An allele that is very prevalent in a population In a heterozygous individual, the allele that determines the phenotype An allele that has no noticeable affect on an organism's phenotype

In a heterozygous individual, the allele that determines the phenotype

The single-factor crosses performed by Mendel support the observation that Multiple Choice if the recessive alleles for two different genes are on the same chromosome, they will never be found within the same gamete. the two alleles for a given gene are distributed randomly among an individual's gametes. the two alleles for a given gene are found within the same gamete. only the dominant alleles for a given trait are found in an organism's gametes. if the dominant alleles for two different genes are on different chromosomes, they will never be found within the same gamete.

the two alleles for a given gene are distributed randomly among an individual's gametes.

Eyelash length is an inherited trait. In the human population, there is an eyelash length gene. There are two possible variants of this gene - an allele for long eyelashes (> 1cm) and an allele for short eyelashes (1 cm or less). The allele for long eyelashes is dominant (L) and the allele for short eyelashes is recessive (l). An individual who is heterozygous for eyelash length would have which of the following phenotypes? Ll ll Long eyelashes LL Short eyelashes

long eyelashes

If you were to examine a typical population at a single locus, you would find more copies of the wild-type allele than any other allele. True or False

true

Human males produce gametes, all contain both an X chromosome and a Y chromosome. sperm, all contain an X chromosome. sperm with neither an X nor a Y; gametes do not contain sex chromosomes. sperm, half contain an X chromosome, half contain a Y chromosome.

sperm, half contain an X chromosome, half contain a Y chromosome.

Color blindness is a recessive X-linked trait. A normal couple has a color-blind child. Who else in this family is probably color blind? the child's paternal grandfather the child's maternal grandmother or grandfather the child's maternal grandfather the child's paternal grandmother the child's maternal grandmother

the child's maternal grandmother

The probability of a couple having either a boy or a girl is ½. However, many families have more boys than girls and VICE VERSA. Why is the observed ratio of boys to girls in typical families different than the predicted ratio? The sex of each child is determined independently. There is a small random sampling error due to the small size of families. Two of the answers are correct. There is a large random sampling error due to the small size of human families and the sex of each child is determined independently. Humans are more heterozygous than is predicted by random sampling. There is a large random sampling error due to the small size of families.

Two of the answers are correct. There is a large random sampling error due to the small size of human families and the sex of each child is determined independently.

An X-linked gene is Multiple Choice a gene on the X chromosome. a gene that encodes traits seen only in females. a gene on the X chromosome that encodes traits seen only in females. a gene that is turned on (makes protein) only when the female hormone estrogen is present. a gene found on any chromosome; they are X-shaped when they are metaphase chromosomes.

a gene on the X chromosome.

Roberts Syndrome is an extremely rare genetic disorder that is characterized by mild to severe prenatal retardation or disruption of cell division, leading to malformation of the bones in the skull, face, arms, and legs. Shown below is a pedigree for a family with Robert's Syndrome. Based on this pedigree Roberts Syndrome is inherited as a(n) ___________ trait? Multiple Choice sex-linked recessive sex-linked dominant autosomal recessive random autosomal dominant

autosomal recessive

Hemophilia A is an X-linked recessive genetic condition. In humans it is due to a mutation in the F8 gene, which encodes a protein called coagulation factor VII. Coagulation factors are proteins important in blood clotting. Individuals with hemophilia, when injured, bleed longer than a normal, healthy individual; the inability to normally clot blood can be life threatening. Hemophilia is much more common in males than in females. Which of the following does NOT explain why this is so? Multiple Choice Males have to receive a defective allele only from their father to get hemophilia A Females have to receive a defective allele from both their mother and their father to get hemophilia A Males are hemizygous for the F8 gene, so they will have hemophilia A if they have one defective allele A female with one defective allele makes enough normal coagulation factor VII to clot blood and will not have hemophilia A

Males have to receive a defective allele only from their father to get hemophilia A

What features of meiosis allow for independent assortment of chromosomes? Random alignment of homologous chromosome pairs on the metaphase plate Separation of sister chromatids Reduction of chromosome number from diploid to haploid Both the separation of sister chromatids and the reduction of chromosome number from diploid to haploid

Random alignment of homologous chromosome pairs on the metaphase plate

A cross between two pea plants results in 732 purple and 268 white plants. What is (are) the genotype(s) and phenotype(s) of the parents that produced these offspring? one parent is homozygous purple, second parent is homozygous white one parent is heterozygous purple, second parent is heterozygous white both parents are heterozygous purple one parent is homozygous purple, second parent is heterozygous white one parent heterozygous purple, second parent homozygous white

both parents are heterozygous purple