Genetics Exam

In garden peas, the pairs of alleles coding for seed shape and seed colour are unlinked. The allele for smooth seeds (S) is dominant over the allele for wrinkled seeds (s). The allele for yellow seeds (Y) is dominant over the allele for green seeds (y). If a plant of genotype Ssyy is crossed with a plant of genotype ssYy, which offspring are recombinants?

C. SsYy and ssyy

What constitutes a linkage group?

A. Genes carried on the same chromosome

The allele for red flower colour (R) in a certain plant is co-dominant with the allele for white flowers (R'). Thus a plant with the genotype RR' has pink flowers. Tall (D) is dominant to dwarf (d). What would be the expected phenotypic ratio from a cross of RR'dd plants with R'R'Dd plants?

C. 1:1:1:1, in which 50% are tall, 50% dwarf, 50% pink and 50% white

Two genes A and B are linked together as shown below.If the genes are far enough apart such that crossing over between the alleles occurs occasionally, which statement is true of the gametes?

D. The number of Ab gametes will be greater than the number of ab gametes.

A polygenic character is controlled by two genes each with two alleles. How many different possible genotypes are there for this character?

C. 9

A cross is performed between two organisms with the genotypes AaBb and aabb.What genotypes in the offspring are the result of recombination?

D. Aabb, aaBb

In peas the allele for round seed (R) is dominant over the allele for wrinkled seed (r). The allele for yellow seed (Y) is dominant over the allele for green seed (y).If two pea plants with the genotypes YyRr and Yyrr are crossed together, what ratio of phenotypes is expected in the offspring?

C. 3 round yellow : 1 round green : 3 wrinkled yellow : 1 wrinkled green

If red (RR) is crossed with white (rr) and produces a pink flower (Rr), and tall (D) is dominant to dwarf (d), what is the phenotypic ratio from a cross of Rr dd and rr Dd?

C. 1:1:1:1, in which 50% are tall, 50% dwarf, 50% pink and 50% white

A single gene in humans causes blood to be either rhesus positive (dominant allele) or rhesus negative (recessive allele). A woman with rhesus negative blood has already had a child with rhesus positive blood. There could be complications during pregnancy if she has another child with rhesus positive blood.What is the probability of this, if the father is the same, and if his mother is known to have rhesus negative blood?

B. 50%

What is the locus of a gene?

C. The position of a gene on a chromosome

What is a sex-linked gene?

B. A gene whose locus is on the X or Y chromosomes.

A gene has three alleles. How many different genotypes can be found for this gene?

B. 6

A cross is carried out between two heterozygous individuals (AaBb) where the genes A and B are not linked genes. What would be the proportions of genotypic recombinants amongst the offspring of this cross?

C. 7

What is the genetic cross called between an individual of unknown genotype and an individual who is homozygous recessive for a particular trait?

A. Test-cross

Which human trait shows a pattern of polygenic inheritance?

C. Skin color

What is a karyotype?

C. Chromosomes arranged in pairs according to their size and shape.

What is the relationship between Mendel's law of segregation and meiosis?

A. Only one of a pair of alleles appears in a gamete.

Which fluid is sampled to try to detect chromosomal abnormalities in a fetus?

C. Amniotic

How does the X chromosome differ from the Y chromosome in humans?

B. Some genes on the X chromosome are absent from the Y chromosome.

How does recombination normally occur for unlinked genes?

B. Random chromosome assortment

Why is it sometimes difficult to identify how certain characteristics are inherited in humans.

C. The inheritance may be polygenic.

Which of the following represents a test cross to determine if phenotype T is homozygous or heterozygous? (Note: allele T is dominant to allele t.)

D. Phenotype T crossed with phenotype t

Which of the following blood group phenotypes always has a homozygous genotype?

D. O

Why is amniotic fluid collected during prenatal testing for abnormal chromosomes?

C. To obtain dissolved chemical by-products of fetal development

What procedure is used to determine whether a chromosome is in excess or missing in an organism?

B. Karyotyping

What feature demonstrates codominance in the inheritance of ABO blood groups?

A. When A antigens and B antigens are present on red blood cells.

Alleles S and T are both dominant. In the theoretical cross ttSs Ttss, which of the following offspring would show recombination?

D. TS, ts

What was the original goal of the Human Genome Project?

B. To determine the nucleotide sequence of all human chromosomes

What does a karyotype show?

B. The number and appearance of chromosomes

A woman has a heterozygous genotype for blood group B. She is expecting a baby with a man who is homozygous Group A. What are the possible blood groups for their baby? I. Group O II. Group A III. Group AB

A. II and III only

A pure breeding tall plant with smooth seeds was crossed with a pure breeding short plant with wrinkled seeds. All the F1 plants were tall with smooth seeds. Two of these F1 plants were crossed and four different phenotypes were obtained in the 320 plants produced.How many tall plants with wrinkled seeds would you expect to find?

C. 60

What are homologous chromosomes?

D. Two chromosomes with the same set of genes, in the same sequence, sometimes with different alleles

Which feature of a genetic pedigree chart demonstrates that a characteristic is sex linked?

B. One gender is more commonly affected than the other.

What does the genotype XH Xh indicate?

C. A heterozygous female

If a purple flowered (Pp) and a white flowered pea plant (pp) are crossed, what will the offspring be?

A. 1 : 1 ratio of purple and white flowers

Hemophilia is sex-linked and is caused by a recessive allele. A woman's father has hemophilia, but her husband does not.What is the probability of the women and her husband having a child with hemophilia?

A.50%

In Drosophila the allele for normal wings (W) is dominant over the allele for vestigal wings (w) and the allele for normal body (G) is dominant over the allele for ebony body (g). If two Drosophila with the genotypes Wwgg and wwGg are crossed together, what ratio of phenotypes is expected in the offspring?

D. 1 × normal wings, normal body : 1 × normal wings, ebony body : 1 × vestigal wings, normal body : 1 × vestigal wings, ebony body

A gene in cattle controls whether horns develop or not. When cattle without horns are mated together, none of the offspring ever has horns. A male with horns is mated with females without horns. If half of the offspring have horns and half do not, what is the conclusion?

B. The male is homozygous recessive.

Humans are in blood group M, N or MN. The alleles for blood group M (M) and blood group N (N) are co-dominant. Humans are also in blood group A, B, AB or O. The alleles controlling these blood groups are IA, IB and i.If two parents have the genotypes ii MM and IA i MN what is the ratio of possible phenotypes of their offspring?

D.1 group A, group M1 group A, group MN1 group O, group M1 group O, group MN

If a man has blood group O and a woman has blood group AB, what is the probability that their child will be blood group O?

A. 0%

1. The diagram below shows the pedigree of a family with red-green colour-blindness, a sex-linked condition.

(a) Define the term sex-linkage.

(b) Deduce, with a reason, whether the allele producing the condition is dominant or recessive.

(c) (i) Determine all the possible genotypes of the individual (2nd Generation-1) using the appropriate symbols.

(c) (ii) Determine all the possible genotypes of the individual (3rd Generation-4) using the appropriate symbols.

(a) Genes located on the X or Y chromosome.

(b) Recessive - 2nd generation 2 and 3 are healthy but have offspring with the condition.

(c) (i) X^h Y

(c) (ii) X^H X^h or X^H X^H

The following diagram represents a two-generation pedigree showing the blood groups of the individuals. The female has been married to two different individuals.

(a) Define the term co-dominant alleles.

(b) Deduce, with a reason, the probable father of 2nd generation–1.

(c) If 2nd generation–3 marries a man with blood group AB, predict the possible genotypes of the children.

(a) Both alleles are expressed equally in the phenotype

(b) A father with AB blood is the only parent who can give a B allele to the offspring

(c) AA, AB, AO, BO (AB x AO or AB x AA)

In Zea mays, the allele for colored seed (C) is dominant over the allele for colorless seed (c). The allele for starchy endosperm (W) is dominant over the allele for waxy endosperm (w). Pure-breeding plants with colored seeds and starchy endosperm were crossed with pure-breeding plants with colorless seeds and waxy endosperm.

(a) State the genotype and the phenotype of the F1 individuals produced as a result of this cross.

(b) The F1 plants were crossed with plants that had the genotype c c w w. Calculate the expected ratio of phenotypes in the F2 generation, assuming that there is independent assortment. Use the space below to show your working.

The observed percentages of phenotypes in the F2 generation are shown below.

coloured starchy 37% colourless starchy 14%

coloured waxy 16% colourless waxy 33%

The observed results differ significantly from the results expected on the basis of independent assortment.

(d) Explain the reasons for the observed results of the cross differing significantly from the expected results.

(a) Genotype: CcWw. Phenotype: Colored, Starchy

(b) Draw a cross between CcWw x ccww. Expected Ratio: 1 CW : 1 Cw : 1 cW : 1 cw

(d) The genes are likely linked and do not independently assort; Cw/cW are recombinants due to crossing over.