GENETICS ASSESSMENT STATEMENTS HIGHER LEVEL
Topic 10: Genetics
10.1 Meiosis
Assessment statement
10.1.1
Example Questions
Describe the behaviour of the chromosomes in A cell replicates its DNA and then starts to divide by meiosis. What is the
the phases of meiosis.
expected arrangement of chromosomes if crossing over has taken place
between the two genes shown?
A.
B.
C.
D.
10.1.2
Outline the formation of chiasmata in the
process of crossing over.
10.1.3
Explain how meiosis results in an effectively
infinite genetic variety in gametes through
crossing over in prophase I and random
orientation in metaphase I.
10.1.4
State Mendel’s law of independent
assortment.
10.1.5
Explain the relationship between Mendel’s law Explain the relationship between Mendel’s law of segregation and meiosis. (3)
law of segregation states that one half of the alleles enter one gamete
of independent assortment and meiosis.
and the other half enter the other gamete;
meiosis reduces the chromosome number by half / diploid to haploid;
homologues carrying alleles separate (in anaphase I);
end result is four cells, half with one allele / homologue and the other half
with the other allele;
Explain how meiosis results in great genetic variety among gametes. (8)
homologous chromosomes form tetrads / bivalents / pairs / undergo
synapsis;
crossing over;
during prophase I;
exchange of DNA / genes / alleles between (non-sister) chromatids /
chromosomes;
description / diagram of chiasma;
new combinations of maternal and paternal genes / alleles / DNA;
bivalents / homologous chromosomes orient / align themselves on equator
randomly;
during metaphase I;
orientation of one homologous pair of chromosomes is independent of
others;
homologous chromosomes separate / move to opposite poles;
independent assortment(of unlinked genes);
leads to 2n / 223 possible gametes (without crossing over);
additional variation when chromatids separate in second division;
10.2 Dihybrid Crosses and Gene Linkage
Assessment statement
Example Questions
10.2.1
Calculate and predict the genotypic and
phenotypic ratio of offspring of dihybrid
crosses involving unlinked autosomal genes.
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?
A.
SsYy and Ssyy
B.
SsYy and ssYy
C.
SsYy and ssyy
D.
Ssyy and ssYy
10.2.2
Distinguish between autosomes and sex
chromosomes.
What is a difference between autosomes and sex chromosomes?
A.
Autosomes are not found in gametes but sex chromosomes are.
B.
Sex chromosomes are found in animal cells and autosomes are found
in plant cells.
C.
Autosomes are diploid and sex chromosomes are haploid.
D.
Sex chromosomes determine gender and autosomes do not.
10.2.3
Explain how crossing over between non-sister What are the possible outcomes of recombination?
I. A different combination of unlinked genes not seen in the parents
chromatids of a homologous pair in prophase I
II. A different combination of linked genes not seen in the parents
can result in an exchange of alleles.
III. The same combination of genes seen in the parents
A.
I and II only
B.
I and III only
C.
II and III only
D.
I, II and III
10.2.4
Define linkage group.
What constitutes a linkage group?
A.
Genes whose loci are on different chromosomes
B.
Genes carried on the same chromosome
C.
Genes controlling a polygenic characteristic
D.
Genes for the inheritance of ABO blood groups
10.2.5
Explain an example of a cross between two
linked genes.
Using an example you have studied, explain a cross between two linked
genes, including the way in which recombinants are produced. (9)
linked genes occur on the same chromosome / chromatid;
genes (tend to be) inherited together /
not separated / do not segregate independently;
non-Mendelian ratio / not 9:3:3:1 / 1:1:1:1;
Real example of two linked genes;
Award [1] for each of the following examples of a
cross between two linked genes.
key for alleles involved in the example of a cross;
homozygous parental genotypes and phenotypes shown;
F1 genotype and phenotype shown /
double heterozygote genotype and phenotype;
possible F2 genotypes and phenotypes shown;
recombinants identified;
recombinants due to crossing over;
in prophase I of meiosis;
diagram / explanation of mutual exchange of parts
of chromatids during crossing over;
10.2.6
Identify which of the offspring are
recombinants in a dihybrid cross involving
linked genes.
10.3 Polygenic Inheritance
Assessment statement
10.3.1
Define polygenic inheritance.
10.3.2
Explain that polygenic inheritance can
contribute to continuous variation using two
examples, one of which must be human skin
colour.
Example Questions
A polygenic character is controlled by two genes each with two alleles. How
many different possible genotypes are there for this character?
A.
2
B.
4
C.
9
D.
16