Genetics Test 1

Klinefelter Syndrome

- 1 in 1000 males -have at least one Y chromosome and more than one X -XXY, XXXY, XXXXY... -tall, small testes, less facial and pubic hair, sterility, normal IQ

Turner Syndrome

-1 in 3000 females -only one X chromosome, an XO genotype -short, low hairline, broad chest, folds of skin on neck, sterility, normal IQ

Principle of Segregation: (Mendel's first law)

-Each individual diploid organism possesses two alleles for any particular characteristic. These two alleles segregate when gametes are formed, and each gamete ends up with one allele

The concept of Dominance:

-When two different alleles are present in a genotype, only the trait encoded by one of them - the "dominant" allele - is observed in the phenotype

Triplo-X Syndrome

-also called Poly-X, these are females with three X chromosomes -1 in 1000 -often fertile with normal IQ -aften taller and thinner -people with more then 3 X chromosomes usually have intellectual dissabilities

XYY (Jacobs) Syndrome

-males with an extra Y chromosome -results from nondisjunction in the male gametes -1 in 1000 males -some people think this shouldn't be called a "syndrome" because these people are often fertile and the same as XY males

A couple are planning to have children and want to calculate the odds that the mother's shoulder dimples will be passed to the children. Shoulder dimples are a dominant trait, the mother's genotype is (Dd) and the father's genotype is (dd). Use the binomial expansion to calculate the odds of having 4 children with shoulder dimples and 1 child without them. (p +q )5 = p 5 + 5p 4q + 10p 3q 2 + 10p 2q 3 + 5pq 4 + q 5 p is the probability of a child having shoulder dimples q is the probability of a child without shoulder dimples

0.16

If you were to roll a ten-sided die twice in a row, what is the probability of obtaining a 7 and then a 9?

1/100

The following two genotypes are crossed: AaBbCcddEe × AabbCcDdEe. What will be the proportion of the genotype AaBbCcDdEe among the progeny of this cross?

1/32

In chickens, congenital baldness is due to a Z-linked recessive gene. A bald rooster is mated with a normal hen. When looking only at the possible females, what percentage of them will be bald?

100% bald

A cross of Aa x Aa would result in a genotypic ratio of _______.

1:2:1

In rabbits, an allelic series helps to determine coat color: C (full color), cch(chinchilla; gray color), ch (Himalayan; white with black extremities), and c (albino; all white). The C allele is dominant to all others, cch is dominant to ch and c, ch is dominant to c, and c is recessive to all the other alleles. This dominance hierarchy can be summarized as C > cch > ch > c. Indicate the phenotypic ratios expected if rabbits with the cross Cc X chc.

2 full color:1 Himalayan:1 albino

Bell pepper color is controlled by the interaction of genes at two loci. The phenotypes are summarized in the table below. What phenotypic ratios would you expect from a cross between a Y+ycc (peach) and Y+yC+c (red) pepper? Genotype Phenotype Y+_ C+_ red Y+_ cc Peach yy C+_ Orange yy cc Cream

3/8 Red, 3/8 Peach, 1/8 Orange, 1/8 Cream

In cucumbers, dull fruit (D) is dominant over glossy fruit (d), orange fruit (R) is dominant over cream fruit (r), and bitter cotyledons (B) are dominant over nonbitter cotyledons (b). The three characters are encoded by genes located on different pairs of chromosomes. A plant homozygous for dull, orange fruit and bitter cotyledons is crossed with a plant that has glossy, cream fruit and nonbitter cotyledons. The F1 are intercrossed to produce the F2. Give the expected proportion of offspring with a dull, orange, and bitter phenotype or a glossy, orange, and bitter phenotype in the F2.

9/16

In cats, curled ears result from an allele (C) that is dominant over an allele (c) for normal ears. Black color results from an independently assorting allele (G) that is dominant over an allele for gray (g). A gray cat homozygous for curled ears is mated with a homozygous black cat with normal ears. All the F1 cats are black and have curled ears. If two of the F1 cats mate, what phenotypes and proportions are expected in the F2?

9/16 black cats, curled ears; 3/16 black cats, normal ears; 3/16 gray cats, curled ears; and 1/16 gray cats, normal ears

In cucumbers, purple fruit color (R) is dominant over cream fruit color (r). A cucumber plant homozygous for purple fruit is crossed with a plant homozygous for cream fruit. Give the genotypes and phenotypes of the offspring of a backcross between the F1 and the cream parent.

Both Purple (Rr) and Cream (rr)

Labrador coat color is an example of recessive epistasis. The B allele controls whether a dog is black or brown and the E allele controls whether or not pigment is suppressed. BlackB_ E_Brownbb E_Yellow_ _ ee A dog breeder liked yellow and brown Labrador retrievers. In an attempt to produce yellow and brown puppies, he mated a yellow Labrador male and a brown Labrador female. Unfortunately, all the puppies produced in this cross were black. How might the breeder go about producing yellow and brown Labradors—which crosses will produce only yellow and brown puppies?

Mating bbEe brown Labradors

Why do sister chromatids remain together in anaphase I of meiosis but separate in anaphase of mitosis and anaphase II of meiosis?

Shugoshin protects cohesin at the centromeres in anaphase I, protecting it from the action of separase.

What would be the consequences to the outcome of meiosis if shugoshin is absent during meiosis?

Sister chromatids could separate along with homologous pairs during anaphase I.

Human blood types are determined by the ABO system. The A and B alleles are codominant and both A and B are dominant over O. If a woman with type B blood has children with a man who has type A blood, what blood types are possible for their children? (Remember, you only know the parents' phenotype, consider all of the possible genotypes when making your Punnett Squares; neither carry alleles for the Bombay phenotype)

Type A, B, AB, or O

In the California poppy, an allele for yellow flowers (C) is dominant over an allele for white flowers (c). At an independently assorting locus, an allele for entire petals (F) is dominant over an allele for fringed petals (f). A plant that is homozygous for yellow and entire petals is crossed with a plant that is white and fringed. A resulting F1 plant is then crossed with a plant that is white and fringed, and the following progeny are produced: 54 yellow and entire, 58 yellow and fringed, 53 white and entire, and 10 white and fringed. Using a chi-square test to compare the observed numbers with those expected for the cross, what can you conclude in regard to whether the ratios observed occurred due to random variations?

With three degrees of freedom, the chi-square value is greater than 12.838 for a probability value of less than 0.005, so the deviation between observed and expected was not likely to occur by chance.

Which of the following codes for a phenotypic human male?

XX with the copy of the SRY gene on an autosomal chromosome

Coat color in cats is determined by genes at several different loci. At one locus on the X chromosome, one allele (X+) encodes black fur; another allele (Xo) encodes orange fur. Females can be black (X+X+), orange (XoXo), or a mixture of orange and black called tortoiseshell (X+Xo). Males are either black (X+Y) or orange (XoY). Bill has a female tortoiseshell cat named Patches. One night, Patches escapes from Bill's house, spends the night out, and mates with a stray male. Patches later gives birth to the following kittens: one orange male, one black male, two tortoiseshell females, and one orange female. What was the genotype of the stray cat with which Patches mated?

XoY

Red-green color blindness in humans is due to an X- linked recessive gene. Both John and Cathy have normal color vision. After 10 years of marriage to John, Cathy has given birth to a color-blind daughter and a color-blind son. John filed for divorce, claiming that he is not the father of at least one of the children. Is John justified in his claim of nonpaternity? (Assume that the daughter is homozygous recessive for the colorblindness allele and both children result from gametes produced from normal meiotic events in both parents.)

Yes. He cannot be the father of Cathy's daughter.

dioecious

an individual either has male or female reproductive structures, but not both

Monoecious

both male and female reproductive structures are found in the same individual

Expressivity

the degree to which a character is expressed

Penetrance

the percentage of individuals having a particular genotype that express the expected phenotype

Discontinuous

there are a limited number of easily distinguishable phenotypes -ABO blood types, pea color, fruit fly eye color

-incomplete penetrance

•Sometimes people inherit the allele, but don't have the expected phenotype

variable expressivity

•When individuals with the allele do have the expected phenotype, the number and functionality of the digit varies

Polygenic characteristics

•encoded by genes at many loci -Polygenic traits are often influenced by environmental factors - multifactorial -Human height

Pleiotropy

•one gene affects multiple characteristics -The lethal allele from the mouse example is pleiotropic because it also affects coat color

Continuous

•there are many possible phenotypes that produce a continuous distribution -Human height -also called quantitative characteristics -Often arise when a phenotype is the result of interactions between genes at multiple loci