CH 16 Mendelian Inheritance Reading Guide Flashcards
What are some examples that lend support to the hypothesis of blending inheritance?
Offspring with resemble the average traits of their parents. Example a flower being purple would have parents that had blue and red flowers.
What are some examples that would reject the hypothesis of blending inheritance hypothesis?
It cannot explain the reappearance of a trait several generations after it has apparently disappeared.
What were some reasons why the garden pea was a good model organism in which to
study heredity? Why not use oak trees or elephants instead?
Relatively faster reproduction rate than other organisms like elephants and he could also produce 1000’s of test subjects
What does it mean for a strain to be true breeding for a particular character, e.g. flower
colour, seed pod colour?
The physical appearance of the offspring in each successive generation is identical to the previous one
What does hybridization mean?
Interbreeding between two different varieties or species of an organism
When crossing plants from different types of true breeding strains, what did Mendel
have to do in order to prevent the ‘mother’ plant from self-fertilizing? (Fig 16.4)
Removed the anthers of the male plant so that it could not self fertilize
What is the relationship between the P1 (often just called P) generation and F1
generation?
P1 is the parental generation
F1 is the First offspring generation
What does it mean that one trait was ‘dominant’? What does it mean that one trait was
‘recessive’?
A trait that appears in the F1 generation is considered dominant and the trait that does not appear is recessive
What does it mean to perform ‘reciprocal’ crosses? Why bother?
Expression of the trait in the female and male parents are interchanges
To show that they yield the same results. Acts as a control
Recall that the recessive trait (e.g. white flower colour) receded/disappeared in the F1
generation. But what actually happened to that trait? Was it destroyed somehow, or just
hidden?
It was not destroyed, but it only has a 1 in 4 chance of being expressed.
How many types of gametes can a true breeding P1 individual make? How many types
of gametes can a heterozygous (for a single gene, e.g. Aa) F1 individual make?
P1 can produce 2 gametes that can contain either A or a but not both
F1 can produce 3 types of zygote AA, Aa or aa
Staying with Figure 16.7, notice that phenotypic and genotypic ratios differ from each
other in the F2. Why is that?
Because there are only 3 types of genotypes AA, Aa and aa with a 1/4 chance of AA, 1/4 chance of aa but a 1/2 chance of Aa
Phenotypes are AA, Aa and aa. With only aa being able to show the recessive trait. Therefore 3/4 chance of dominant trait being expressed
Are all F2 individuals that show the recessive phenotype going to be true breeding?
What does the Punnett square predict?
Yes
Are all F2 individuals that show the dominant phenotype going to be true breeding?
What does the Punnett square predict?
No
How can you find out the actual genotype of an individual that displays a dominant
phenotype, given that such an individual could be either homozygous (AA), or
heterozygous (Aa)?
If left to self fertilize the AA should only produce A (yellow seeds) phenotype. While the Aa will produce a (green seeds) in a 3:1 ratio. 3 yellow to 1 green
Why does the ratio of non-true breeding to true breeding F2s break down into a 2:1
ratio, rather than a 3:1 ratio as we encountered in a different context earlier in our
discussion?
Because you’ve removed the true breeding (recessive genotype) from the group
How does a testcross work?
Crossing an unknown genotype with a homozygous recessive genotype
A parent with a dominant phenotype; what can you say for sure about their genotype?
what can you not know?
Genotype is not aa but you cannot know if its not Aa or AA.
What kind of kitten ratios would you expect if you crossed a heterozygous short-haired
cat (Ss) to a homozygous recessive long-haired cat (ss)? What if you crossed a
homozygous short-haired cat (SS) to a homozygous recessive long-haired cat (ss)?
Relate this to Figure 16.8.
2/4 would be Ss and 2/4 would be ss
What happens in meiosis (and when during
meiosis) to separate alleles that are carried on homologous chromosomes from each
other? Relate to Fig 16.9.
Segregation of the homologous chromosomes separate in Anaphase 1.
Practice the meiosis finger dance.
OK
What is incomplete dominance?
The phenotype of the heterozygous genotypes is intermediate between those of the homozygous genotypes.
Consider an individual of genotype Aa, what is the probability that an egg made by this
individual carries the A allele of the gene? what is the probability (p) that an egg made
by this individual carries the a allele of the gene?
1/2 chance of A and 1/2 chance of a
If two Aa individuals have offspring together, what is the probability that they have an
AA baby?
Use Punnet Square
1/4 chance of AA
