Genetics

Problem Solving Booklet

Complete the following questions in your jotter. Don’t forget to state the meaning of your alleles and to draw Punnett squares for each question.

  1. Gregor Mendel, the father of modern genetics, developed his theory of inheritance using pea plants.
  1. In pea plants, tallness is dominant over shortness. If two heterozygous tall plants are crossed, what will be the genotypes and phenotypes of all possible offspring? (Use T= tall plant and t= short plant)
  2. Carry out crosses with plants of the following genotypes. For each cross show phenotypes, genotypes, gametes formed and possible genotypic ratios and phenotypic ratios in the F1 using punnet squares where necessary.

i)TTX tt

ii)Tt X Tt

iii)Tt X TT

iv)Tt X tt

  1. In guinea pigs, the allele for short hair is dominant.
  1. What genotype would a heterozygous short haired guinea pig have?
  2. What genotype would a purebreeding short haired guinea pig have?
  3. What genotype would a long haired guinea pig have?
  4. Show the cross for a pure breeding short haired guinea pig and a long haired guinea pig.
  5. What percentage of the offspring will have short hair?
  6. Show the cross for two heterozygous guinea pigs.

i.What percentage of the offspring will have short hair?

ii.What percentage of the offspring will have long hair?

  1. The ability to roll the tongue is dominant over the inability to do so in humans.

Use T=tongue-rolling and t=non-tongue-rolling.

a. If two heterozygous tongue-rollers have children, what genotypes and phenotypes could their children have?

b. If a non-tongue-roller has children with a homozygous tongue-roller, what will their children's genotypes and phenotypes be?

  1. If black mice are dominant over white mice, predict the genotype and phenotype of a cross between a purebred (homozygous) black mouse with a purebred white mouse.
  1. If brown eyes are dominant over blue eyes in Huskies, predict the genotype and phenotype of a cross between two heterozygous brown eyed Huskies.
  1. One cat carries heterozygous, long-haired traits (Ss), and its mate carries homozygous short-haired traits (ss). Use a Punnett square to determine the genotype, phenotype and probability of all of their offspring.
  1. If red roses are dominant over white roses, predict the genotype and phenotype of a cross between a purebred red rose with a purebred white rose.
  1. In humans brown eyes are dominant over blue eyes. Suppose a blue eyed man marries a brown eyed woman whose father was blue eyed. What proportion of their children would be expected to have blue eyes?
  1. A brown eyed man whose father was brown eyed and whose mother was blue eyed married a blue eyed woman whose father and mother were both brown eyed. The couple have a blue eyed son. For which of the individuals can you be sure of the genotypes?
  1. A heterozygous round seeded plant (Rr) is crossed with a homozygous round seeded plant (RR).

What percentage of the offspring will be homozygous (RR)?

  1. A homozygous round seeded plant is crossed with a homozygous wrinkled seeded plant.
  1. What are the genotypes of the parents?
  2. What percentage of the offspring will also be homozygous?
  1. In pea plants purple flowers are dominant to white flowers.
  1. If two white flowered plants are cross, what percentage of their offspring will be white flowered?
  1. A white flowered plant is crossed with a plant that is heterozygous for the trait.

What percentage of the offspring will have purple flowers?

  1. Two plants, both heterozygous for the gene that controls flower color are crossed.

i.What percentage of their offspring will have purple flowers?

ii.What percentage will have white flowers?

  1. In certain breeds of dogs, deafness is due to a recessive allele (d) of a particular gene,

and normal hearing is due to its dominant allele (D).

  1. What percentage of the offspring ofa normal heterozygous (Dd) dog and a deaf dog (dd) would be expected to have normalhearing?
  1. A homozygous deaf dog and a homozygous normal?
  1. In man, normal pigmentation is due to a dominant allele (C), and albinism to its recessive

allele (c). A normal man marries an albino woman. Their first child is albino. What are

the genotypes of these three people? If there have more children, what would they

probably be like?

  1. In minks, brown is dominant over silver-blue colour. What offspring would you predict ifyou crossed a homozygous brown mink with a silver-blue mink?
  1. In foxes, silver-black coat colour is governed by a recessive allele (b) and red colour by its dominant allele (B). Determine the genotypic and phenotypic ratios expected from the mating of a homozygous red fox with a heterozygous red fox.
  1. In humans, polydactyly (which causes the formation of extra fingers or toes) is due to a dominant gene, P. When one parent is heterozygous for polydactyly and the other is normal, what will be the expected frequency of polydactyly in their children?
  1. Curly hair is dominant over straight hair. Is it possible for a curly haired man to produce curly haired children if his wife has straight hair? Use a Punnett square to determine your answer. (use the letter C).
  1. The ability to taste sodium benzoate is due to a dominant gene, T. If everyone in the Smith family of 14 individuals is a taster except for Poncho, does this mean that Poncho is adopted?
  1. Several black guinea pigs of the same genotype were mated and produced 29 black and 9 white offspring. (use the letter B)
  1. What would you predict the genotypes of the parents to be?
  2. Why?
  1. In question 3 you learned about the alleles for tongue rolling. In the following family tree some members can roll their tongue and some cannot.
  1. Copy & complete the diagram to show the missing genotypes and phenotypes.

Grandfather – roller (Tt)Grandmother – roller ( ?? )

Father - non roller ( ?? ) Mother – roller (TT)

Son - ______( ?? )Daughter - ______(?? )

  1. Name two individuals who have the same phenotype but different genotypes.
  1. Name a person who is homozygous for the:
  1. dominant trait ii. recessive trait.

Pedigree Chart Activity

All living things have pedigrees. A pedigree is a diagram that shows the occurrence and appearance (phenotype) of a particular genetic trait, as it is passed from one generation to the next in a given family. From this information, along with an understanding of inheritance, genotypes of individuals can often be determined.

Symbols for a Pedigree Chart

Follow the story below and create a pedigree chart.

This is the story of Grandma and Grandpa Flipnob, and their clan! They were married way back in 1933 and have been just like newlyweds ever since. From their union, 4 individuals were created. Elizabeth, the eldest, was born in 1935. Fred soon followed in 1936. In 1939 Michelle was brought into this world. Mickey, a surprise to the whole family was the baby of the family, not being born until 1950.

Elizabeth fell in love at a young age, and wed her high school sweetheart, David, in 1954. From this marriage, two bundles of joy came about (at the same time):

John and Sonny – 1955 (twins!)

It took Fred a little longer to find his soul mate. Finally in 1970, Fred found the woman of his dreams, Wilma, and they were married. Since they married so late in life, they only brought one new person into this world:

Barney – 1972

Michelle was a hard working woman, and never found time in her schedule for love. She led a very productive and fulfilling life, but she never did marry and have children.

Mickey was a wild one! After a long string of girlfriends, he finally chose Monica to spend the rest of his life with. They were wed in 1975 and brought two girls into this world:

Krista – 1977

Janet – 1979

Draw the pedigree chart in your jotter.

Answer the following questions:

  1. Who are the in-laws?
  1. What is the relationship between the people in the third generation?

Now that you have your pedigree chart together, shade the appropriate circles and squares using the information below.

Remember that individuals who possess the RECESSIVE trait are to be filled in completely. Individuals not shaded in carry at least one dominant allele.

Dominant/Recessive Inheritance – Freckles

Not having freckles is a recessive trait.

Grandpa Flipnob did not have freckles, but his beautiful bride did.

Fred and Michelle were the only two of their siblings to have freckles.

Of the grandchildren, the twins did not have freckles, and neither did Barney, but the two girls did.

Using the guide provided, determine the genotypes of all individuals in this pedigree chart for freckles. Remember, having no freckles is a RECESSIVE trait.

STEP 1

Assign two recessive genes to any person on the pedigree whose symbol is shaded. Small letters are written below the person’s symbol.

STEP 2

Assign one dominant gene to any person on the pedigree whose symbol is unshaded. A capital letter is written below the person’s symbol.

STEP 3

Use the information given to you to determine the second alleles for each person with the dominant phenotype.

Example: We know that Grandpa Flipnob does not have freckles. If Grandma were BB, could any bb children be produced from Grandma and Grandpa? If Grandma were Bb, could any bb children be produced from them? Complete Punnett squares below to determine your answer.

  1. From your results, what is Grandma’s genotype?
  2. What must be the genotypes of their children?
  3. What are the genotypes of their grandchildren?
  4. Label your pedigree with the correct genotypes for each generation.