Exam 19: Introduction to Genetics

Susan, a mother with type B blood, has a child with type O blood. She claims that Craig, who has type A blood, is the father. He claims that he cannot possibly be the father. Further blood tests ordered by the judge reveal that Craig is AA. The judge rules that

In humans, normal skin pigmentation is influenced by a dominant gene ( C ) which allows pigmentation to develop. All individuals who are homozygous for the recessive allele ( c ) are unable to produce an enzyme needed for melanin formation and are therefore referred to as albino. Two normal parents produce an albino child. What are the chances that the next child will be an albino?

In summer squash, spherical-shaped fruit has been shown to be dominant to elongated fruit. On one occasion, two different spherical varieties were crossed and produced all disk-shaped fruits. When these hybrid disk-shaped fruits were crossed, they produced 75 disk-shaped fruits, 48 spherical fruits, and 9 elongated fruits. Explain.

In tomatoes, red ( R ) is dominant to yellow ( r ), tall ( D ) is dominant to dwarf ( d ), and smooth ( H ) is dominant to peach or hairy ( h ). (a) How many different genotypes are there in relationship to these three characteristics? (b) How many different phenotypes are there in relationship to these three characteristics? (c) How many different homozygous pure-breeding forms can be produced?

Multiple effects of a single gene is known as

There is a color pattern inherited in certain mice in which agouti (gray) is homozygous, and yellow is heterozygous. A cross of two yellows produces two yellows for each agouti. A second gene, C/c , controls the expression of the color genes: C is the dominant allele that allows color to be expressed, and the recessive gene in the homozygous condition ( cc ) prevents any color from being expressed. (a) Give the genotypes of a white parent crossed with a yellow parent that produces 1/2 white, 1/3 yellow, 1/6 agouti offspring. (b) Give the results of the cross of two forms heterozygous for each gene. (c) Can you develop a pure-breed population for any of the colors?

A genetic disease causing an abnormal attachment of muscles to the bones of the little finger is

Horses In horses, black coat color is influenced by the dominant allele ( B ) and chestnut coat color by the recessive allele ( b ). Trotting gait is due to a dominant gene ( T ), pacing gait to the recessive allele ( t ). Use this information to answer the following question(s). In the horses example above, what color horse would you use to find out the genotype of a black trotter? Give the genotype and phenotype.

The theory of segregation

The theory of independent assortment

Some dogs have erect ears; others have drooping ears. Some dogs bark when following a scent; others are silent. Erect ears and barking are due to dominant alleles located on different chromosomes. A dog homozygous for both dominant traits is mated to a droopy-eared, silent follower. The phenotypic ratio expected in the F ₁ is

The number of different alleles for ABO blood types in the total human population is

The alleles an individual inherits are the

If one parent has blood type A and the other parent has blood type B, then which of the following blood types is possible in the children?

When an allele's effect on a trait masks that of an allele paired with it, the first allele is referred to as

In poultry, the genes for rose comb ( R ) and pea comb ( P ) produce walnut whenever they occur together ( R _ P _); single-combed individuals have the homozygous condition for both genes ( rr pp ). (a) Give the F ₁ and F ₂ phenotypic results of a cross of a pure-breeding rose comb ( RR pp ) with a pure-breeding pea comb ( rr PP ). (b) Give the phenotypic results of a cross of Rr Pp x rr Pp . (c) Give the phenotypic results of a cross of RR Pp x rr Pp . (d) Give the phenotypic results of a cross of Rr pp x rr Pp . (e) Give the phenotypic results of a cross of Rr Pp x rr pp .

If two parent organisms have different alleles for a gene that an experimenter wants to test, he or she will perform a

What fraction of the time will a cross of Aa BB cc with Aa Bb CC produce an offspring of genotype Aa Bb CC ?

Garden Peas In garden peas, one pair of alleles controls the height of the plant and a second pair of alleles controls flower color. The allele for tall ( D ) is dominant to the allele for dwarf ( d ), and the allele for purple ( P ) is dominant to the allele for white ( p ). Use this information to answer the following question(s). In the garden peas example above, a tall plant with purple flowers crossed with a dwarf plant with white flowers produces 1/2 tall with purple flowers and 1/2 tall with white flowers. What is the genotype of the parents?

Which of the following is a disease caused by a pleiotropic gene?