Meiosis & Genetic Diversity
Homologous Chromosomes are
chromosomes that are the same length, have the same centromere position, contain the same genetic information. (the two version of chromosome 1 you got from mom and dad are homologs)
Using the letters A & B to represent 2 different traits, show us what a dihybrid cross would look like.
AaBb x AaBb
Explain what Non-mendelian genetics is.
inheritance of traits that seem to break Mendel's laws. More complicated mode of inheritance.
When one gene affects the expression of another gene
Epistasis
In a certain species of plants, the stems can either be tall or short. Hybrids for this trait will be tall. This is an example of
complete dominance
What is the chiasmata?
The region on homologous chromosomes that experiences crossing over
What is the difference between haploid and diploid cells?
Haploid cells contain half the number of chromosomes as the individual organism. Diploid contain full.
What does hemizygous refer to?
Males only have one X chromosome. They will inherit any/all diseases on that one chromosome.
If a disorder affects more males than females in a population, it would be logical to think the trait is inherited how?
X chromosome
Trisomy 21 also known as Downs Syndrome, is caused by an error made during meiosis where homologous chromosomes fail to separate from one another during anaphase. This is known as
non disjunction
Why are the 4 gametes produced during meiosis said to be "unique", even thought 2 come from your maternal DNA and 2 from your paternal.
Crossing over occurs between 2 of them.
In rats, brown coloring (B) is dominant to albino coloring (b) and scaly tails (S) is dominant to smooth tails (s).
Cross BbSs x Bbss
What fraction of the offspring would be albino with scaly tails?
1/8
A certain flower species can be orange (YY), white (yy), or yellow (Yy). This is an example of
Incomplete dominance
We are looking at two traits in plants. Flower color (P) and stem length (T). We see the offspring have a recombination frequency of less than 50%, what does this mean?
The genes are linked. They travel as a unit and are separated by crossing over much less frequently than expected.
Height and skin color are both examples of traits that are due to this type of inheritance
polygenic
in your own words, describe the three ways in which meiosis can lead to genetic variation?
random fertilization of sperm and egg
crossing over
independent assortment of chromosomes
Two parental plants are crossed and 2 of their traits are observed in their offspring: flower color (P) & stem length (T).
The results show:
91 purple, tall plants
28 purple, short plants
33 white, tall plants
11 white, short plants
What conclusions can we make?
dihybrid cross
Give an example of phenotypic plasticity.
Temperature can change coat color in rabbits and Siamese cats
Soil pH can affect flower color
UV exposure can increase melanin production in the skin
You have a Chi Squared value of 5.95. You compare this number to the Chi-Square Table and see the significant number is 5.99. What does this mean?
You accept the null hypothesis - any difference between observed and expected is due to random chance.
Take a look at the pedigree on the board. What is the most logical assumption for how this disease is inherited?
x linked dominant
Identify the stages and explain the 3 key differences in Meiosis & Mitosis
Prophase I: Synapsis & Crossing Over (tetrads form)
Metaphase I: Tetrads line up on metaphase plate
Anaphase I: Homologous Chromosomes separate
Describe independent assortment and the law of segregation
IA - genes inherited for one trait are not connected to genes inherited for another trait (we learned later this isn't always true)
LoS - the two versions of a gene (alleles) will be separated into different gametes during meiosis.
Anhidrotic Ectodermal Dysplasia: Females heterozygous for this mutation exhibit a mosaic, patchwork skin pattern where some patches possess sweat glands and others do not .
Name the process that results in these patches, explain why this process is necessary.
x inactivation
to prevent over expression of x-linked genes
Create a linkage map for the following:
Gene - Recombination Frequency
A-B - 13.2%
B-C - 18.5%
A-C - 5.3%
B A C
Two individuals RrTtYy are crossed. What is the probability their offspring has the genotype RRttyy?
1/64