BISC 160 Test 4 Review 1 - ANSWER KEY
Test 4:
1.​ Genetic diversity
2.​ E is a homologous pair and F is a homologous pair
3.​ Answer
a.​ Yes - sister chromatid D will also have recessive allele (r) because sister
chromatids are identical.
b.​ No - the other chromosome of pair E must have that gene but its allele could be T
or t. Homologous pairs are composed of one chromosome from mom and one
from dad; they are not identical like sister chromatids.
4.​ Different versions of the same gene
5.​ Haploid
6.​ Answer
a.​ Homologous chromosomes
b.​ Sister chromatids
c.​ Meiosis I
7.​ Answer
a.​ Mitosis: happens in somatic cells; creates 2 identical daughter cells; only goes
through one division; occurs in all eukaryotes; in anaphase, sister chromatids are
separated; results in diploid organisms
b.​ Meiosis: happens in germ cells; creates 4 haploid daughter cells that are different
from their parent cells; independent assortment causes genetic variation; goes
through two divisions; tetrads form in meiosis I; occurs in organisms that do
sexual reproduction; in anaphase I, homologous chromosomes are separated,
and in anaphase II, sister chromatids are separated
8.​ Independent assortment
9.​ Answer
a.​ Law of segregation: each cell gets only one copy of each chromosome
b.​ Law of independent assortment: the homologous pairs line up at the metaphase
plate completely independent of how other chromosomes line up -- leads to
different combinations of alleles
10.​Same centromere position, same length, same genes, same gene order, and same gene
locus
11.​Refers to incorrect number of chromosomes; results from errors in meiosis
12.​Answer
a.​ Complete dominance- the dominant allele is always phenotypically expressed
b.​ Incomplete dominance- heterozygotes have a new, different phenotype
(intermediate)
c.​ Codominance- both alleles are expressed equally
d.​ Sex-linked- occur on sex chromosomes (X or Y)
13.​Answer
a.​ Genotypic ratio: 1:2:1
b.​ Phenotypic ratio: 3:1
14.​Answer
a.​ Mutation (generate genetic variation within a population)
b.​ Genetic drift (occurs at random within a population, change in allele frequencies
over time)
c.​ Gene flow (moving genes between populations)
d.​ Selection (acts directly on the phenotype, variation in heritable traits)
e.​ Non-random mating (preference for mating with those that will lead to
reproductive success)
15.​p² + 2pq + q² = 1; p² = frequency of homozygous dominant individuals; 2pq = frequency
of heterozygous individuals; q² = frequency of homozygous recessive individuals
16.​Answer
a.​ Stabilizing- mean stays the same but the extremes are reduced (less variability)
b.​ Directional- becomes more advantageous to have one phenotype over another
c.​ Disruptive- extremes are favored over intermediates (increases population
variability)
17.​X-inactivation -- one of the x chromosomes in every cell in the female body is turned off
a.​ Females are referred to as mosaics because different genes may be turned off in
different cells
18.​The gametophyte is a (unicellular/multicellular), (haploid/diploid) organism. The
sporophyte is a (unicellular/multicellular), (haploid/diploid) organism.
19.​Prophase I
20.​AO, BO, AB, OO
21.​Crossing over is the exchange of genetic material between homologous, non-sister
chromatids, resulting in genetic variation.
22.​A homozygote will have two copies of the same gene (same alleles on both
chromosomes), while a heterozygote will have different copies of the same gene (two
different alleles on the homologous chromosomes)
23.​A trait is the outcome of a character. For example, two characters Mendel studied were
flower color and plant height; however, the traits would be purple or white and tall or
short.
24.​If traits were not heritable, they would not be able to be passed down between
generations. Genes would not play a role in characteristics.
25.​
Since polydactyly is a dominant trait, 50% of his offspring
should have polydactyly.
26.​Prezygotic: can not form a zygote; Postzygotic: organism can be formed but can not
reproduce
27.​Epistasis is when one locus masks the effect of another locus. For example, the
labrador’s coat color is affected by the locus that codes for pigment deposition.
28.​Populations are made of individuals, and the genes/alleles contained within each
individual make up the gene pool.
29.​0.32
30.​Bottleneck events; founder effects
31.​Answer:
a.​
b.​ Metaphase: all chromosomes line up with the centromere at the midline
c.​ Metaphase I: homologous chromosome pairs line up at the midline
d.​ Metaphase II: the remaining chromosomes in the cell after meiosis I line up with
the centromere at the midline
32.​Haplo-Diplontic Life Cycle
a.​
33.​ Diplontic Life Cycle
a.​
34.​Mitosis or meiosis as seen above in the life cycles
35.​See below:
a.​ There is random mating
b.​ No gene flow
c.​ No mutation
d.​ No genetic drift
e.​ No selection