Biol 113 Test 3 Preparatory Notes

Meiosis

Questions:
Chromosome Language:




Homologous Chromosomes: A
Sister Chomatids: N/A
Gene: B
Alle: C

Remeber genes are segments of DNA that code for a protein or trait and alleles are versions of a
gene

1. Choose which is true
a. Haploid cells have one allele per gene
b. Haploid cells gave two alleles per gene
2. Diploid = 2n, with n being the number of chromosomes, so therefore
a. Haploid = n
b. Haploid = 3n
3. Fill in the number: Humans equal = 2, 23. Fruit flies, who have 4 chromosomes and are
diploid = 2, 4.


Meiosis
Meiosis: the cellular division that splits chromosomes so that the result is 4 daughter haploid
cells
There are two divisions:
- Meiosis I: separates homologous chromosomes while replicated sister chromatids stay
together in the two daughter cells
- Meiosis II: the two daughter cells divide again to separate the sister chromatids into two
additional daughter cells
+ Results in 4 haploid daughter cells
The Cell cycle is basically the same for mitosis and meiosis
Mitosis: G1, S, G2, Mitosis, C, back to G1…

,Meiosis: G1, S, G2, Meiosis I, C, Meiosis II, C, back to G1…




Chromosome movement:
In Mitosis we end up with diploid cells and in meiosis we end up with haploid cells




Question:




1. Which metaphase plate alignment occurs during mitosis and which occurs during
meiosis
A: Mitosis
B: Meiosis
2. Which cell is one of the results of mitosis and meiosis.

, D: Mitosis
C: Meiosis
Variation
The result of Meiosis is 4 haploid daughter cells that are genetically distinct from each other ad
the parent cell
Two places of genetics variation
- Crossing over: occurs in late prophase I (Meiosis I) paternal and maternal homologs
exchange genetic material
- Independant assortment: when homologous chromosomes line up at the metaphase
plate during meiosis I, they line up independently from


Crossing Over
Crossing over: occurs in late prophase I (Meiosis I) paternal and maternal homologs exchange
genetic material




Crossing results in chromosomes with a combination of maternal and paternal segments and
thus a mixture of maternal and paternal alleles
- REMEMBER IT IS RANDOM

Independent Assortment
Independent assortment: when homologous chromosomes line up at the metaphase plate
during meiosis I, they line up independently from each other

, The random alignment of chromosomes at Metaphase I plate contributes to the genetic diversity
of gametes




During Independent assortment, homologous chromosomes assort and separate independently
of each other during meiosis I. So that the resulting cells have a mixture of chromosomes from
mom and dad
- REMEMBER IT IS RANDOM

Questions:
Independent Assortment-In humans, the ability to digest lactose beyond childhood is
determined by a single gene on Chromosome 1. L denotes the allele that gives the ability to
digest lactose and I denotes the inability to digest lactose. On chromosome 3 is the gene for
widows' peak. A denotes the allele for no widow's peak and a denotes a widow's peak. A woman
volunteers to be a participant in a genetic research study. Her genotype is LlAa. A doctor
harvests a single egg from the body. The genotype of her egg is LA. How did her chromosomes
line uo at the metaphase plate during meiosis?
C




Crossing Over- In the barbary figure genome, the gene for color for the and the gene for spine
size and the gene for drought resistance are located right next to each other on chromosome 1.
Below is a diagram of the placement of the genees on hcromosome 1 for an AaBbCc individual.
Crossing over is more likely to occur between alleles of which genes?