Download Ch 11 Reviewing this Chapter answers

Ch 11 Reviewing this Chapter
1) How did Mendel’s procedure differ from that of his predecessors? What is his theory of
inheritance called? Mendel’s procedures differed from that of his predecessors because he
applied mathematics to biology. He also took detailed observation and notes. Mendel’s
theory of inheritance is called a particulate theory; it is based on the existence of
hereditary units called genes.
2) 2. How does the F2 of Mendel’s one-trait cross refute the blending concept of inheritance? Using
Mendel’s one-trait cross as an example, trace his reasoning to arrive at the law of segregation.
The F2 generation of Mendel’s one strait cross refuted the blending concept of inheritance
because there were three tall plants and one short plant, there was no a “blend” to create a
medium height plant. If the blending concept were to hold truth, then all plants would share
equal traits of parents and they would all be medium in height but this was not the case. While 75%
of the offspring will be physically like their parents due to expressing the dominant allele, 25% will
express the recessive allele that would seem to “suddenly” appear because it skipped a generation.
3) Using Mendel’s two-trait cross as an example, trace his reasoning to arrive at the law of
independent assortment.
According to the law of independence the factors for height and colour would segregate
independently. As shown with the two-cross method when a homozygous dominant tall and
green plant bred with a homozygous recessive short and yellow plant, there were 4 different
outcomes – a tall plant that was green, a tall plant that was yellow, a short plant that was green,
and a short plant that was yellow. This means all the factors separate independently of each other.
P generation plants differ in two regards—length of the stem and colour of the pod. The F1 generation
shows only the dominant traits, but all possible phenotypes appear among the F2 generation. The
9:3:3:1 ratio allowed Mendel to deduce that factors segregate into gametes independently of other
factors.
4) What are the two laws of probability, and how do they apply to a Punnett square? The two laws
of probability are the product rule which states that we have to multiply the chances of
independent events to get answers and the product rule which states that when the same
event can occur in more than one way we can add the results. They apply to the Punnet
square because the Punnet square shows us the probability.
5) What is a testcross, and when is it used ? Test crosses are crosses between an individual with
the dominant phenotype and an individual with the recessive phenotype (and genotype) and
the resulting phenotypic ratio tells us whether the dominant phenotype is homozygous or
heterozygous. They are used when determining whether an individual with a dominant
phenotype is homozygous dominant or heterozygous.
6) How might you distinguish an autosomal dominant trait from an autosomal recessive trait when
viewing a pedigree? In autosomal recessive disorders most affected children have normal
parents, and heterozygotes are unaffected, and two affected parents will always have an
affected child. In autosomal dominant disorders affected children will usually have affected
parents, heterozygotes are affected, two affected parents can produce normal children, and
two unaffected parents will not have affected children.
7) For autosomal recessive disorders, what are the chances of two carriers having an affected child
¼ chance
8) For most autosomal dominant disorders, what are the chances of a heterozygote and a normal
individual having an affected child?
½ chance
9) Explain inheritance by multiple alleles. List the human blood types, and give the possible genotypes
for each.
When multiple alleles control traits, the gene exists in several allelic forms. For example,
three types of allele can determine the blood type but it is only controlled by a single gene
pair
Phenotype
Genotype
A
IA IA, IAi
B
IB IB , IBi
AB
IA IB
O
ii
10) Explain the inheritance of incompletely dominant alleles and why this is not an example of
blending inheritance Incomplete dominance is when the heterozygote has an intermediate
phenotype between that of either homozygote. This is not blending because when an
incomplete dominant flower, which is pink, reproduces its offspring appear white, red, and
pink.
11) Explain why traits controlled by polygenes show continuous variation and produce a distribution in
the F2 generation that follows a bell-shaped curve Polygenic inheritance :when a trait is
determined by two or more sets of alleles. Each dominant allele has an effect on the
phenotype, which creates an additive affect. This creates the bell shape in graphs
12) How do you recognize a pedigree for an X-linked recessive allele in human beings?
In X-linked recessive disorders more males than females are affected, an unaffected son
can have two normal phenotype parents, for the female to be affected her father must have
it and her mother must have it or be a carrier, the characteristic often skips generations, and
if a female has it all her sons must have it.