CROSSOVER PROBLEMS 1. In a study of crossovers the following map distances were determined: gene G to L = 34 map units, gene L to X = 9 map units, and gene X to gene G = 43 map units. Draw the chromosomes with the genes in their relative positions. 2. The sites of four gene loci on a chromosome are based on the following crossover frequencies. Draw the relative positions of the four genes. A and B: 40% B and C: 20% C and D: 10% C and A: 20% D and B: 10% 3. In a series of breeding experiments, a linkage group composed of genes A, B, C, D, and E was found to have the following recombination frequencies: GENE A B C D B 8 C 12 4 D 4 12 16 E 1 9 13 3 4.The crossover percentage between genes O and J is 10%, N and M is 11%, J and N is 20%, O and M is 41%. What is the sequence of genes on the chromosome? What is the sequence of genes on the chromosome?
CROSSOVER PROBLEMS- 5. The genes producing the recessive fruit fly traits of hairy body (h) and ebony color (c ) are closely linked on the third chromosome (They are almost always inherited together). What are the expected phenotype ratios of the second generation when a fly purebred for both dominant traits is crossed with a fly purebred for both recessive traits? Normal bristles (H) and gray body color (C ) are the corresponding dominant traits. CONTINUED 6. The crossover percentage between genes Q and R is 30%; between Q and S is 35%; and between R and S is 5%. What is the correct gene sequence? 7. The following crossover percentages between genes were obtained: Z and W 5%; W and Y 5%; X and Y 10%; Z and Y 10%; and between Z and X 15%. What is the correct gene sequence? 8. Lois Lane Kent s husband has passed on to their daughter two strange straits: x-ray vision (X) and muscles like steel (M). Information that Mr. Kent was given during his journey from the planet Krypton states that the genes for these two traits are dominant and that the vision and muscle loci are 16 map units apart on the same chromosome. Assuming that an earthman will someday marry her daughter, Lois is worried about the chances that her grandchildren will inherit the genes that have made their mother such a difficult child to raise. What is the probability that Ms. Kent s grandchildren will have both traits?
PRACTICE LINKOVER A chromosome in humans is known to contain ten separate genes that ware linked to each other. Test crosses from numerous couples were compiled with the following information obtained. Draw the chromosome with the genes in their relative positions. GENE ORDER K I B MAP UNITS 15 30 GENE ORDER C I J MAP UNITS 11 15 GENE ORDER I B G MAP UNITS 28 19 GENE ORDER G B D MAP UNITS 17 21 GENE ORDER A G B MAP UNITS 2 18 GENE ORDER J G H MAP UNITS 32 29 GENE ORDER A E H MAP UNITS 9 16 GENE ORDER K C D MAP UNITS 4 17 DNA
SEX-LINKED PROBLEMS 1. Red-green color blindness is due to a recessive sex-lined trait. A mother who is the carrier of red-green color blindness, but who has normal vision, has a son. The father is not color blind. What chance does their son have of having normal vision? 2. The disease hemophilia is due to a recessive sex-lined trait. What is the probability of a hemophilic man passing on this trait to his son? 3. What is the probability of a couple having five sons in a row? 4. In fruit flies, white eyes is a recessive sex-linked trait: long wings are incomplete dominant with short wings. A homozygous red-eyed female fruit fly with medium wings is crossed with a white-eyed male fruit fly that has long wings. How many of their first 1000 offspring would be males with red eyes and long wings?
SEX-LINKED PROBLEMS- CONTINUED 5. Brown spotted teeth in humans is due to a dominant sexlinked trait. What percent of the daughters would you expect to have spotted teeth when a man with spotted teeth marries a woman with normal white teeth? 6. In poultry, ovary removal results in the forming of testes. Thus a female can become converted to a male, producing sperm and developing male secondary sex characters. If such a male is mated to a normal female, what sex ratio occurs in the offspring? 7. Color in cats is due to a sex-linked trait. The heterozygous condition results in a calico cat. A calico cat has a litter of eight kittens: 1 yellow male, 2 black males, 2 yellow females, and 3 calico females. What was the color of the male parent? 8. Red-green colorblindness in humans is a sex-linked recessive trait. If one in every 12 human males shows this trait, how common is it among human females?
PROBLEMS WITH SEX 1. Holandric genes are those that are located on the Y chromosome with no matching gene on the X chromosome. A male student s father has the holandric trait of hairy ear lobes. The student s mother and all of her relatives have never had airy earlobes. What is the probability of the student developing hairy ears later in life? 2. Another male student has all of his male relatives on his mother s side with hairy ears and all of his male relatives on his father s side with no hairy ears. Will the student develop hairy ears later on in life? 3. A hairy chest is a sex-limited trait due to a single dominant gene. A woman heterozygous for a hairy chest but who of course does no have a hairy chest herself marries a man without a hairy chest. What percent of their sons would you expect to develop a hairy chest? 4. A heavy beard is a sex-limited trait due to a dominant gene over a light beard. Large mammary glands are partially dominant with small breasts and are also sex-limited. When a man homozygous for a heavy beard and heterozygous for breast size marries a woman homozygous for a light beard and medium sized breasts. What phenotypes and their ratios are expected in their children?
PROBLEMS WITH SEX- 5. In the middle ages, church choirs would at times castrate boys in the choir who were extremely good tenures. Would castration would have worked for their intended purpose? CONTINUED 6. Today, many clinics offer free sterilization to men through vasectomy. This operation cuts and ties off the tubes that sperm cells usually travel through. Would you expect any appearance or disappearance of sex-limited traits in these men? Explain why or why not. 7. Index finger length is due to a sex-influenced trait. Long index fingers are dominant in males and recessive in females. What are the phenotype ratios that would result from a cross between a woman with long index fingers and a man with short index fingers? 8. Harelip is due to a sex-influenced trait that is dominant in males. If a heterozygous man with a harelip marries a homozygous woman without a harelip, what percentage of the man s sons should develop harelips?
PRACTICE QUIZ 1. A homozygous for tall bean plant was crossed with a homozygous for short bean plant. All the offspring were of a medium height. What phenotype ratios would be expected in the second generation? 2. When a purebred tall wheat plant is crossed with a purebred short wheat plant all of the offspring are of a very short height., what percent of the offspring would expect to be very short if one of the very short plants is crossed with the original tall plant? 3. In pigeons, the checkered pattern is dependant on a dominant gene (C ) and the plain on the recessive allele (c ). Red color is controlled by a dominant gene (B) and the brown color by the recessive allele (b). What are the expect4ed phenotype ratios when a checkered red pigeon (CcBb) is crossed with a checkered brown pigeon (Ccbb)? 4. Red-green color blindness is due to a recessive sex-linked trait. A colorblind woman marries a normal visioned man. What percent of their daughters should have normal vision?
PRACTICE QUIZ- 5. White eyes in fruit flies is due to a recessive sex-linked gene; vestigial wings (underdeveloped wings) are due to an autosomal recessive gene. What percent of the offspring would you expect to be white-eyed males with normal wings when a red-eyed vestigial winged male is crossed with a white-eyed female that is purebred for normal wings? CONTINUED 6. Achrondoplastic dwarfism is due to a lethal dominant trait. Free earlobes are dominant over attached earlobes. A dwarf with free earlobes marries a normal height woman with free earlobes. Both people had fathers with attached earlobes. What are the chances of the couple having a child that is a dwarf with free earlobes like the father? 7. OOPS! Another mix-up with the name tags in the maternity war. Once again it is up to you to match up the parents with the correct babies by using blood types. COUPLES BLOOD TYPES BABIES BLOOD TYPES 8. A woman marries a man without the holandric trait for hairy ears. She has always disliked this trait that all the males in her family have had. What is the chance that their baby boy will develop hairy ears later on in life? COUPLE 1: AB x O COUPLE 2: AB x AB COUPLE 3: B x A BABY Q: O BABY R: A BABY S: AB