GENETICS BOOK PROBLEMS #2 (Pg

GENETICS BOOK PROBLEMS #2 (pg. 272-273; #1, 5, 6, 11, 13, 14, 17)

1. In some plants, a true-breeding, red-flowered gives all pink flowers when crossed with a white-flowered strain: CRCR (red) X CrCr (White)  CRCr (Pink). If flower position (axial or terminal) is inherited as it is in peas (see Table 14.1), what will be the ratios of genotypes and phenotypes of the F1 generation resulting from the following cross: axial-red (true-breeding) X terminal-white? What will be the ratios in the F2 generation?

A= axial (dominant) a= terminal (recessive) R= red, r=white, Rr= pink (pink can also be notated as RW if you call the white allele “W”)

P= AARR x aarr  F1= 100% AaRr (genotype); 100% axial-pink (phenotype) to get F2, cross AaRr x AaRr

AR Ar aR ar AR AARR AARr AaRR AaRr Ar AARr Aarr AaRr Aarr aR AaRR AaRr aaRR aaRr ar AaRr Aarr aaRr aarr

Genotypic Ratio: 1/16 AARR 1/16 aarr 2/16 AARr 2/16 aaRr 2/16 AaRr 1/16 aaRR 4/16 AaRr 1/16 Aarr 2/16 Aarr

Phenotypic Ratio: 3/16 Axial-red 1/16 Terminal-red 6/16 (3/8) Axial-pink 2/16 (1/8) Terminal-pink 3/16 Axial-white 1/16 Terminal-white

5. A man with type-A blood marries a woman with type-B blood. Their child has type-O blood. What are the genotypes of these individuals? What other genotypes, and in what frequencies, would you expect in offspring from this marriage? Man= AO (IA IO) Woman= BO (IB IO) Child= OO (i i)

IA IO IB AB BO iO AO OO

Phenotypic ratios: ¼ AB ¼ A ¼ B ¼ O 6. Phenylketonuria (PKU) is an inherited disease caused by a recessive allele. If a woman and her husband, who are both carriers, have three children, what is the probability of each of the following? a. All three children are of normal phenotype. (¾ x ¾ x ¾) = 27/64 b. One or more of the three children have the disease. 1 – 27/64 = 37/64 Note: Remember that the probabilities of all possible outcomes always add up to 1. c. All three children have the disease. (¼ x ¼ x ¼) = 1/64 d. At least one child is phenotypically normal. 1 – 1/64 = 63/64

11. Imagine that a newly discovered, recessively inherited disease is expressed only in individuals with type- O blood, although the disease and blood group are independently inherited. A normal man with type-A blood and a normal woman with type-B blood already have one child with the disease. The woman is now pregnant for a second time. What is the probability that the second child will also have the disease? Assume that both parents are heterozygous for the gene that causes the disease. d= inherit disease D= no disease Man: AODd Woman: BODd Child #1: OOdd Child #2: 1/16 chance will have the disease ¼ chance OO x ¼ chance dd

13. In corn plants, a dominant allele I inhibits kernel color, while the recessive allele i permits color when homozygous. At a different locus, the dominant allele P causes purple kernel color, while the homozygous recessive genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the offspring? P: IiPp x IiPp IP Ip iP ip IP IIPP IIPp IiPP IiPp Ip IIPp IIpp IiPp Iipp iP IiPP IiPp iiPP iiPp ip IiPp Iipp iiPp iipp

Phenotypic ratio: 12 no color: 3 purple: 1 red (3/4 no color: 3/16 purple: 1/16 red) 14. The pedigree below traces the inheritance of alkaptonuria, a biochemical disorder. Affected individuals, indicated here by the colored circles and squares, are unable to break down a substance called alkapton, which colors the urine and stains body tissues. Does alkaptonuria appear to be caused by a dominant allele or by a recessive allele? Fill in the genotypes of the individuals whose genotypes can be deduced. What genotypes are possible for each of the other individuals?

Recessive allele

George: Aa Michael: Aa Arlene: aa Daniel: Aa Sandra: A- (AA or Aa) Alan: Aa Tom: aa Tina: A- (AA or Aa) Sam: Aa Carla: aa Wilma: aa Christopher: A- (AA or Aa) Ann: Aa

17. In mice, Black (B) is dominant to white (b). At a different locus, a dominant allele (A) produces a band of yellow just below the tip of each hair in mice with black fur. This gives a frosted appearance known as agouti. Expression of the recessive allele (a) results in a solid coat color. If mice that are heterozygous at both loci are crossed, what is the expected phenotypic ratio of their offspring?

Cross: AaBb x AaBb

AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb

Phenotypic ratio: 9 agouti: 3 solid black: 4 white