General BIO 1 Ch. 9

All the offspring of a cross between a black-eyed Mendelian and an orange-eyed Mendelian have black eyes. What is the expected phenotypic ratio of a cross between two orange-eyed Mendelians?

0 black-eyed:1 orange-eyed

If one parent is blood type AB and the other is type O, what fraction of their offspring is expected to have blood type A?

0.5

How many sex chromosomes are in a human gamete?

1

Part complete In a situation in which genes assort independently, what is the ratio of the gametes produced by an AaBB individual?

1 AB : 1 aB

Black eyes are dominant to orange eyes, and green skin is dominant to white skin. Sam, a MendAlien with black eyes and green skin, has a parent with orange eyes and white skin. Carole is a MendAlien with orange eyes and white skin. If Sam and Carole wereto mate, the predicted phenotypic ratio of their offspring would be _____.

1 black eyes, green skin : 1 black eyes, white skin : 1 orange eyes, green skin : 1 orange eyes, white skin

An individual heterozygous for eye color, skin color, and number of eyes mates with an individual who is homozygous recessive for all three characters; what would be the expected phenotypic ratio of their offspring? [Hint: B = black eyes, b = orangeeyes; G = green skin, g = white skin; C = two eyes, c = one eye]

1 black eyes, green skin, two eyes : 1 black eyes, green skin, one eye : 1 black eyes, white skin, two eyes : 1 black eyes, white skin, one eye : 1 orange eyes, green skin, two eyes : 1 orange eyes, green skin, one eye : 1 orange eyes, white skin, twoeyes : 1 orange eyes, white skin, one eye

Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). What proportion of the offspring from the cross PpRr × PpRr are expected to have white flowers and wrinkled seeds?

1/16

In a standard monohybrid cross between purple-flowered and white-flowered peas, in which purple flowers are dominant, what fraction of the purple-flowered peas in the F2 generation would you expect to be true-breeding?

1/3

Assume that in cattle a spotted coat is dominant to an even coat, short horns are dominant to long horns, and the traits for coat type and horn length assort independently. In a cross between cattle that are each heterozygous for both traits, what proportion of their offspring are expected to have long horns?

1/4

Part complete Three characteristics assort independently in one species of insect: Red eyes (R) are dominant to black eyes (r). Blue wings (B) are dominant to white wings (b). Green bodies (G) are dominant to yellow bodies (g). A cross is made between two heterozygous insects (RrBbGg). What is the probability that the offspring will be homozygous dominant for all three characteristics?

1/64

High levels of LDL cholesterol in the bloodstream can be the result of familial hypercholesterolemia, an inherited condition that displays incomplete dominance. In a family with a severely affected father and an unaffected mother, what percentage of their children are expected to have higher than normal blood cholesterol?

100%

Assuming that the probability of having a female child is 50% and the probability of having a male child is also 50%, what is the probability that a couple's first-born child will be female and that their second-born child will be male?

25%

A woman who is a carrier of hemophilia marries a man affected with hemophilia. What percentage of their sons and daughters is expected to have hemophilia?

50% of sons and 50% of daughters

Part complete In Labrador retrievers, a common breed of dog, black coat is dominant to chocolate, normal vision is dominant to progressive retinal atrophy (PRA), and normal hip joint is dominant to hip dysplasia. All these genes assort independently. Two dogs that are heterozygous for alleles of all three genes are crossed. Using rules of probability (not a Punnett square), what is the chance that the first pup born to these dogs will be chocolate, have normal vision, and have normal hip joints?

9/64

If A is dominant to a and B is dominant to b, what is the expected phenotypic ratio of the cross AaBb × AaBb?

9:3:3:1

The disease hemophilia is caused by a single gene that is located on the X chromosome. Because human females have two X chromosomes (XX), they have two copies of this gene. Since hemophilia is recessive (h), a female must have two copies of the recessive allele to have the disease. A human male (XY), on the other hand, has only one X chromosome, and so needs only one copy of the recessive allele to have the disease. Complete the Punnett square below of a cross between a carrier mother (a female who carries one copy of the recessive allele and so appears normal herself) and a non-hemophiliac father. 1.Drag the pink labels to the pink targets to indicate the sex dictated by the genotype in each box. (Pink labels may be used more than once.) 2.Drag the blue labels to the blue targets to indicate whether the genotype in each box confers hemophilia, normal, or carrier status. (Blue labels may be used more than once.)

A. Female; B. Normal; C. Male; D. Normal; E. Female; F. Carrier; G. Male; H. Hemophiliac.

Mendel discovered that the allele for green seed pods (G) is dominant to the allele for yellow seed pods (g). He crossed true-breeding (homozygous) parental plants with green (GG) and yellow (gg) seed pods to produce an F1 generation, all of which were heterozygous (Gg) with green seed pods. He then crossed two of these F1 plants to produce an F2 generation.Drag the genotypes and phenotypes from the left to correctly complete the Punnett square for the F2 generation. Drag only blue labels to blue targets and pink labels to pink targets. Labels may be used more than once.

A. GG; B. Green pea pod; C. Gc; D. Green pea pod; E. Gg; F. Green pea pod; G. gg; H. Yellow pea pod

Drag the terms to their correct locations on the figure below.

A. Homologous chromosomes; B. Gene locus; C. Recessive allele; D. Centromere; E. Sister chromatids; F. Alleles; G. Dominant allele

Human ABO blood type is determined by a single gene that comes in 3 distinct alleles: IA , IB , and i. The IA and IB alleles are each dominant to the i allele, but are codominant with each other, meaning that both phenotypes are expressed in the heterozygote. The Punnett square below shows a cross between two parents with different blood types. Drag the genotypes and phenotypes from the left to correctly complete the Punnett square.

A. IaIb; B. Type AB; C. Iai; D. Type A; E. Ibi; F. Type B; G. ii; H. Type O

You have one tree that produces big yellow apples and another tree that produces small red apples. When the two are crossed, you find that half the offspring trees produce big red apples and half produce big yellow apples. What are the genotypes of the parents? A = big apples; a = small apples; R = red apples; r = yellow apples.

AArr and aaRr

Most human genes come in alternate versions called _________.

Alleles

Which of the following statements regarding genotypes and phenotypes is false?

An organism with two different alleles for a single trait is said to be homozygous for that trait.

In the following cross the genotype of the female parent is BbGg. What is the genotype of the male parent? [Hint: B = black eyes, b = orange eyes, G = green skin, g = white skin]

BBGg

A _________ is an inherited feature that varies from individual to individual.

Character

Which of the following statements regarding prenatal testing is false?

Chorionic villus sampling is typically performed later in the pregnancy than amniocentesis

Part complete Imagine that long fins in zebrafish is a dominant trait. A breeder wants to set up a breeding program beginning with homozygous dominant long-finned fish. If she obtains a handful of the long-finned fish, how can she tell which, if any, of these are homozygous for the trait?

Cross the long-finned fish with short-finned fish; if the offspring are all long-finned, the long-finned parent is homozygous.

In Morgan's testcross of a gray-bodied, long-winged heterozygous female Drosophila with a homozygous recessive black-bodied, vestigial-winged male, the following offspring were obtained: 965 gray body, long wing; 944 black body, vestigial wing; 206 gray body, vestigial wing; 185 black body, long wing. Focusing only on the recombinant classes (gray body, vestigial wing and black body, long wing), the numbers of offspring of each type are similar (206 and 185). What accounts for the similar number of offspring of each recombinant phenotype?

Crossing over between chromosomes is reciprocal, so whenever a recombinant chromosome of one type is produced, there's a recombinant of the opposite type that is also produced.

Dr. Smith's parents have normal hearing. However, Dr. Smith has an inherited form of deafness. Deafness is a recessive trait that is associated with the abnormal allele d. The normal allele at this locus, associated with normal hearing, is D. Dr. Smith's parents could have which of the following genotypes?

Dd and Dd

If an organism has two non-identical versions of a gene, the one that is expressed in the organism is called the __________ allele.

Dominant

Part complete An insect that has the genotype EeGGcc will have the same phenotype as an insect with the genotype __________.

EEGgcc

Two normal parents have three normal children: one son and two daughters. Their son and one of their daughters marry and also have normal children. Their second daughter, Mary, marries a man with a rare, recessive blood disorder. They have two children, and both children develop the blood disorder. What must be true of the genotypes of Mary's parents?

Either one of her parents or both of her parents were heterozygous for the trait.

Part complete The chromosome theory of inheritance is based upon which of the following sets of observations?

Genes segregate; chromosomes come in pairs.

The __________ is the genetic makeup of an organism.

Genotype

Imagine that a deaf male has a child with a hearing female. You know that the male must have the genotype dd, but the female could be either Dd or DD. If the couple's first child has hearing, can you determine the mother's genotype? (Hint: Draw Punnett squares for the two possible crosses.)

Her genotype cannot be determined.

A carrier of a genetic disorder who does not show symptoms is most likely to be ________ to transmit it to offspring.

Heterozygous for the trait and able

Imagine that beak color in a finch species is controlled by a single gene. You mate a finch homozygous for orange (pigmented) beak with a finch homozygous for ivory (unpigmented) beak and get numerous offspring, all of which have a pale, ivory-orange beak. This pattern of color expression is most likely to be an example of

Incomplete dominance

All the offspring of a cross between a red-flowered plant and a white-flowered plant have pink flowers. This means that the allele for red flowers is ________ to the allele for white flowers.

Incompletely dominant

In breeding pure-breeding large and small strains of mice, you cross individuals of each strain and note that their offspring are intermediate in size. Two models (explanations) to account for this result are (1) that body size in these strains is due to one gene with alleles that show incomplete dominance and (2) that body size is a polygenic trait. How could you distinguish between these models?

Intercross the F1 and see if the F2 contains three size classes (consistent with the incomplete dominance model) or if there is a range of sizes (consistent with the polygenic model).

Why are lethal dominant alleles so much more rare than lethal recessive alleles?

Lethal dominant alleles are harmful whether they are carried in homozygous or heterozygous form, so there is always strong selection against these alleles.

Akin to urban legends, there are curious genetics legends - things like eye color being determined by one gene, with a brown eye allele being completely dominant to blue. The problem comes when simple myth meets the complex reality of how eye color and many other traits are transmitted. Why is the inheritance of so many traits difficult to explain using only Mendel's view of genetics?

Mendel was correct for the traits he investigated, but his principles must be extended (not discarded) to explain many more complex patterns of inheritance.

A BbGg x bbgg cross yields a phenotypic ratio of approximately 5 black eyes, green skin : 5 orange eyes, white skin : 1 black eyes, white skin : 1 orange eyes, green skin. Which of the following best explains these results?

Mendel's law of independent assortment is being violated.

The observed distribution of alleles into gametes is an illustration of _____.

Mendel's laws of segregation and independent assortment

A genetic cross involving parents that differ in a single character is called a _______________.

Monohybrid cross

Which of the following statements regarding genetic testing is false?

Most human genetic diseases are treatable if caught early

Which of the following statements best explains why dominant alleles that cause lethal disorders are less common than recessive alleles that cause lethal disorders?

Most individuals carrying a lethal dominant allele have the disorder and die before they reproduce, whereas individuals carrying a lethal recessive allele are more likely to be healthy and reproduce

Most people afflicted with recessive disorders are born to parents who were

Not affected by the disease

You are trying to determine if a newborn boy has an X-linked genetic disorder by analyzing a family pedigree. Which of these findings would rule out the X-linked hypothesis?

Only the females in the pedigree have the disorder and none of the males do.

Mendel conducted his most memorable experiments on

Peas

The physical traits of an organism are called its ___________.

Phenotype

If an organism has two non-identical versions of a gene, the one that is not expressed in the organism is called the _________ allele.

Recessive

Most genetic disorders of humans are caused by

Recessive Alleles

Which of the following statements regarding sickle-cell disease is false?

Sickle-cell disease causes white blood cells to be sickle-shaped

The existence of rare XY individuals who are phenotypically normal women was instrumental in learning about human sex determination. Maleness is determined by the SRY gene found on the Y chromosome. How is it possible to be an XY woman?

The SRY locus of the Y chromosome is deleted

What is the most likely explanation for the occurrence of an X-linked genetic disorder in the boy at the bottom of the pedigree shown?

The boy has a new mutation for the disorder

Use the Punnett square from the introduction and the ones you drew for Part A to select the three statements that are true about the inheritance of this form of deafness.

The child of a deaf man and a DD hearing woman will definitely have hearing. If a deaf man and a hearing woman have a deaf child, the mother's genotype must be Dd. If a deaf child is born to hearing parents, both parents must be Dd.

A colorblind woman marries a man who is not colorblind. All of their sons, but none of their daughters, are colorblind. Which of the following statements correctly explains these results?

The gene for color vision is found on the X chromosome

Imagine that a mutant strain of Drosophila undergoes crossing over at half the normal rate. How would a genetic map prepared for this mutant differ from a genetic map prepared for a normal (wild type) fly?

The order of genes would be the same in both strains, but the distances measured between genes in the mutant would be half those of the wild type

Imagine you're counseling a couple who have undergone carrier screening for Tay-Sachs disease. The man is a carrier, and the woman does not carry the Tay-Sachs allele. How should you advise them?

They should be informed that if they have a child, the child will not have Tay-Sachs disease but will have a 50% chance of being a carrier of the Tay-Sachs allele.

A _______ is one particular variation of a character.

Trait

The sex chromosome complement of a normal human female is

XX

We can better understand our ancestry by analyzing the __________ in males

Y chromosome

Previously, it was thought that the blending hypothesis explained inheritance. The blending hypothesis maintained that __________.

after a mating, genes of the two parents are mixed in the offspring and lose their individual identities

What type of inheritance fits the data in this pedigree?

autosomal recessive

In order to determine the genotype of a MendAlien with black eyes and green skin, you would cross this individual with a(n) _____ individual.

bbgg

Part complete What is the genotype of the parent with orange eyes and white skin? (Note: orange eyes are recessive.)

bbgg

A phenotypic ratio of 9:3:3:1 in the offspring of a cross indicates that _____.

both parents are heterozygous for both genes

A cross between two individuals with black eyes and green skin which results in an individual with orange eyes and white skin is an example of a _____ cross.

dihybrid

Mendel's law of independent assortment states that

each pair of alleles (chromosomes) segregates independently of the other pairs of alleles during gamete formation

Which of the following is an example of incomplete dominance in humans?

hypercholesterolemia

Two identical twins are raised in different environments. They possess _____ genotypes and _____ phenotypes.

identical ... variable

John and Jane are planning a family, but each has a brother who has sickle-cell disease, so they are concerned that their children may develop sickle-cell disease. Neither John nor Jane nor their respective parents have the disease. They consult a genetic counselor who tells them that __________.

it's possible that they cannot produce a child with sickle-cell disease, but blood tests on them both will be required to make sure

Amniocentesis and chorionic villus sampling allow for ________ and ________ of the fetus so that it can be tested for abnormalities.

karyotyping; biochemical testing

Sex-linked conditions are more common in men than in women because

men need to inherit only one copy of the recessive allele for the condition to be fully expressed

What is the normal complement of sex chromosomes in a human male?

one X chromosome and one Y chromosome

Sickle-cell disease is an example of

pleiotropy

Which plants in this figure must all be heterozygous?

purple-flowered plants in the F1 generation

A man and his wife are having trouble having a baby. Using modern technologies, the woman's eggs are removed, fertilized with her husband's sperm, and implanted into her uterus. The procedure is successful, and the woman gives birth to a healthy baby boy. After a while, though, they discover that their son is colorblind and has blood type O. The woman claims that the child can't be theirs since she has blood type A and her husband has type B. Also, neither parent is colorblind, although one grandparent (the woman's father) is also colorblind. In regard to the baby's colorblindness, a sex-linked recessive trait, you explain that

since colorblindness is sex-linked, a son can inherit colorblindness if his mother has the recessive colorblindness allele.

Recessive X-linked traits are more likely to be expressed in a male fruit fly than a female fruit fly because

the male's phenotype results entirely from his single X-linked gene

In people with sickle-cell disease, red blood cells break down, clump, and clog blood vessels. Blood vessels and broken cells accumulate in the spleen. Among other symptoms, this leads to physical weakness, heart failure, pain, and brain damage. Such a suite of symptoms can be explained by __________.

the pleiotropic effects of the sickle-cell allele

In a monohybrid cross, F2 refers to __________.

the second filial generation, or the "grandchildren" of the original mating pair

Varieties of plants in which self-fertilization produces offspring that are identical to the parents are referred to as

true-breeding

Mendel's view of the mechanism of heredity was radically different from the prevailing view of the time because he saw heredity working through __________.

unchanging (immutable) heritable factors that were contributed by each parent and never altered by mixing

If the two characteristics that Mendel looked at in his dihybrid cross of smooth yellow peas with wrinkled green peas had been controlled by genes that were located close together on the same chromosome, then the F2 generation __________.

would have deviated from the 9:3:3:1 phenotypic ratio that is predicted by the law of independent assortment