IBIO 341: Sex effects in transmission genetics and pedigree analysis

Shown below are two graphs that plot the percentage of fertilized eggs containing males against the atmospheric temperature during early development in (a) snapping turtles and (b) most lizards. Which of the following statements are consistent with the data presented?

In snapping turtles, sex determination is strongly influenced by temperatures such that males are favored in the 26-34ºC range. Lizards appear to have their sex determined by factors other than temperature in the 20-40ºC range.

An insect species is discovered in which the heterogametic sex is unknown. An X-linked recessive mutation for reduced wing (rw) is discovered. A. Select the resulting phenotypes of F1 generation from a cross between a female with reduced wings and a male with normal-sized wings assuming the female is the heterogametic sex. B. Select the resulting phenotypes of F2 generation from a cross between a female with reduced wings and a male with normal-sized wings assuming the female is the heterogametic sex. C. Select the resulting phenotypes of F1 generation from a cross between a female with reduced wings and a male with normal-sized wings assuming the male is the heterogametic sex. D. Select the resulting phenotypes of F2 generation from a cross between a female with reduced wings and a male with normal-sized wings assuming the male is the heterogametic sex. Check all that apply.

A male, normal wings female, normal wings B female, reduced wings male, normal wings female, normal wings C male, reduced wings female, normal wings D female, reduced wings male, reduced wings female, normal wings male, normal wings

In one of Morgan's experiments, he crossed his newly discovered white-eyed male with a red-eyed female. (Note that all of the females at that time were homozygous for red eyes because the allele for white eyes had not yet propagated through Morgan's flies.) All of the F1 flies produced by this cross (both males and females) had red eyes. Next, Morgan crossed the red-eyed F1 males with the red-eyed F1 females to produce an F2 generation. The Punnett square below shows Morgan's cross of the F1 males with the F1 females. Drag the labels to their appropriate locations to complete the Punnett square for Morgan's F1 x F1 cross. Drag pink labels onto the pink targets to indicate the alleles carried by the gametes (sperm and egg). Drag blue labels onto the blue targets to indicate the possible genotypes of the offspring. Labels can be used once, more than once, or not at all.

F1 male gametes w+ Y F1 female gametes w+ w Female offspring w+w+, w+w Male offspring w+Y, wY When a homozygous red-eyed female was crossed with the white-eyed male (w+w+ × wY), the resulting F1 females were w+w and the F1 males were w+ Y. Crossing the F1 males and F1 females would yield these results: All the F2 females would have red eyes, although some would be homozygous (w+w+ ) and others would be heterozygous (w+w). Half the F2 males would have red eyes (w+ Y), and half would have white eyes (wY).

When Gregor Mendel conducted his genetic experiments with pea plants, he observed that a trait's inheritance pattern was the same regardless of whether the trait was inherited from the maternal or paternal parent. Mendel made these observations by carrying out reciprocal crosses: For example, he first crossed a female plant homozygous for yellow seeds with a male plant homozygous for green seeds, and then crossed a female plant homozygous for green seeds with a male plant homozygous for yellow seeds. Unlike Mendel, however, Morgan obtained very different results when he carried out reciprocal crosses involving eye color in his fruit flies. The diagram below shows Morgan's reciprocal cross: He first crossed a homozygous red-eyed female with a white-eyed male, and then crossed a homozygous white-eyed female with a red-eyed male. Drag the labels to their appropriate locations to complete the Punnett squares for Morgan's reciprocal cross. Drag blue labels onto the blue targets to indicate the genotypes of the parents and offspring. Drag pink labels onto the pink targets to indicate the genetic makeup of the gametes (sperm and egg). Labels can be used once, more than once, or not at all.

First half of reciprocal cross: Male wY, male gamete w Y Female w+w+, female gametes w+ Female offspring: w+w Male offspring w+Y Second half of reciprocal cross: Male w+Y, male gametes w+ Y Female ww, female gametes w Female offspring: w+w Male offspring: wY When Morgan crossed a homozygous red-eyed female with a white-eyed male, all of the offspring had red eyes. However, in the reciprocal cross (homozygous white-eyed female with a red-eyed male), all of the females had red eyes while all of the males had white eyes.

Red-green color blindness is due to an X-linked recessive allele in humans. A widow's peak (a hairline that comes to a peak in the middle of the forehead) is due to an autosomal dominant allele. Consider the following family history: A man with a widow's peak and normal color vision marries a color-blind woman with a straight hairline. The man's father had a straight hairline, as did both of the woman's parents. Use the family history to make predictions about the couple's children. Drag the correct label to the appropriate location in the table. Not all labels will be used.

If the couple has a child, what is the chance it will be a son with a widow's peak? 1/4 What is the chance that any son the couple has will be color blind with a straight hairline? 1/2 What is the chance that any daughter that the couple has will be color blind with a widow's peak? 0 Suppose the couple had a daughter with normal color vision and a widow's peak. What is the chance that she is heterozygous for both genes? 1

You now know that inheritance of eye color in fruit flies is sex-linked: The gene encoding eye color is located on the X chromosome, and there is no corresponding gene on the Y chromosome. How would the inheritance pattern differ if the gene for eye color were instead located on an autosome (a non-sex chromosome)? Recall that for autosomes, both chromosomes of a homologous pair carry the same genes in the same locations. Suppose that a geneticist crossed a large number of white-eyed females with red-eyed males. Consider two separate cases: Case 1: Eye color exhibits sex-linked inheritance. Case 2: Eye color exhibits autosomal (non-sex-linked) inheritance. (Note: In this case, assume that the red-eyed males are homozygous.) For each case, predict how many of the male and female offspring would have red eyes and white eyes. Drag the correct numbers on the left to complete the sentences on the right. Numbers can be used once, more than once, or not at all.

Case 1: If there were 100 female offspring, 100 would have red eyes and 0 would have white eyes. If there were 100 male offspring, 0 would have red eyes and 100 would have white eyes. Case 2: If there were 100 female offspring, 100 would have red eyes and 0 would have white eyes. If there were 100 male offspring, 100 would have red eyes and 0 would have white eyes.

The inheritance of eye color in Drosophila is controlled by genes on each of the fly's four chromosome pairs. One eye-color gene is on the fly's X chromosome, so the trait is inherited in a sex-linked manner. For this sex-linked trait, the wild-type (brick red) allele is dominant over the mutant vermilion (bright red) allele. A homozygous wild-type female fly is mated with a vermilion male fly X+X+ x X(v)Y Predict the eye colors of F1 and F2 generations. (Assume that the F1 flies are allowed to interbreed to produce the F2 generation.) Drag the correct label to the appropriate location in the table. Labels can be used once, more than once, or not at all.

F1 females: all wild type F1 males: all wild type F2 females: all wild type F2 males: half wild type, half vermilion

Eye color in Drosophila is an X-linked trait. White eyes is recessive to red eyes. If a Drosophila male has white eyes, which of the following must also be true?

His mother had at least one white allele. Because this male had white eyes, he must have inherited a white allele from his mother.

For X-linked traits in Drosophila, the male phenotype is determined by the maternally inherited allele.

True Males inherit only one X chromosome. That chromosome is contributed by the female parent.

Consider the following family history: Bob has a genetic condition that affects his skin. Bob's wife, Eleanor, has normal skin. No one in Eleanor's family has ever had the skin condition. Bob and Eleanor have a large family. Of their eleven children, all six of their sons have normal skin, but all five of their daughters have the same skin condition as Bob. Based on Bob and Eleanor's family history, what inheritance pattern does the skin condition most likely follow?

X-linked dominant If the skin condition is caused by an X-linked dominant allele, a father would pass the allele on to all of his daughters, who would all have the skin condition. In contrast, the father would not pass the allele on to any of his sons because the sons would receive the father's Y chromosome, not his X chromosome. As a result, none of the sons would inherit the skin condition.

White eye color is an X-linked trait in one line of fruit flies. White eyes is recessive to red eyes. If a red-eyed female and a white-eyed male are crossed, _______.

some of their male progeny may have white eyes If the female is heterozygous, approximately half of the male progeny will have white eyes.