- Alleles
- Genotype
- Haplotype
- Locus
- Different sequences that may exist at a difference locus
- Two alleles that are present in an individual at a given locus. Heterozygous means two different alleles are present. Homozygous means they are the same allele.
- A linear order of closely linked alleles usually inherited as a unit.
- Specific location or map position of a gene or marker.
- Meiosis
How many rounds of replication and division are involved?
When do homologous chromosomes pair?
What is the result?
One round of replication followed by two rounds of division.
Meiosis 1= maternal and paternal chromosomes pair. the only time that replicated homologous chromosomes come together and pair.
**This is where recombination Occurs**
RESULT= two 1N gametes
Chromatid.
Describe pre-replication?
Describe post replication?
What is the final product?
Pre replication (G1) chromosome in one linear stranded DNA molecule.
Post replication each product of replication is a chromatid, joined by a single centromere to form a single chromosome.
Two sister chromatids are the identical products of one round of reolication
- Diploid
- Haploid
- (2n = 46) chromosomes. Diploid Chromosome content is 2C
- (1n = 23) chromosomes. Haploid chromosome content is 1C
**During Mitosis or Meiosis the Cromosome content will be 4C
Mitosis
How many rounds of replication and division take place?
What type of tissue does this take place in?
What is the result?
One diploid cell going through one round of replication and one round of division
Somatic Tissue
2 diploid daugher cells
Independent Assortment
Unlinked Loci are transmitted independently during mitosis and meiosis.
Describe Segregation in meiotic and mitotic divisions.
Genes occure in pairs, with equal chance for each allele to be transmitted to the offspring.
Recombination
- What is recombination and when does it happen?
- What deterimines the probability of 2 loci crossing over
- What forms between the sister chromatids
- What advantage does it offer the species
- Physical exchange of sister chromatids during the pairing of homologous chromosomes. Occurs in Prophase 1
- Probability is a funcion of distance, further away is less likely. Cell has 46 croms and 23 homologous pairs. One to two corssovers per homologous pairs.
- Chiasma forms at the site of crossing over.
- Increases genetic diversity
What is linkage?
What is linkage disequlibrium and what does it result in ?
- Close relation of loci on the same chromosome
- Co-occurance of alleles on the same chromosome more often than by chance. Over reprentation of specific haplotypes
Independent Assortment
1.Describe the results of meiosis for
Loci A & B
- Describe independent assortment for Loci A & D.
- Loci A and B are unlinked and on separate chromosomes therefore gametes AB, Ab, aB, ab. will be of equal probability
- Loci A and D are on the same chromosome but are far enough apart to be unlinked. Therefore we have the equal probability to get gamete, AD Ad aD ad.
- Describe the gametes formed for Loci A and E
- Loci A and E are linked due to the proximity of the two loci. They will produce AE and ae 90% of the time. Very rarely will you get crossing over at loci this closely related.
Describe the linkage disequlibrium for HAPLOTYPE A1A2 or a1a2.
There is very tight linkage between loci of the same haplotype and VERY rarely will they be separated. In this case the gamemes will be A1A2 or a1a2.
What is a haplotype block and how will it affect independent assortment?
A haplotype of gene loci that occure between two recombination hotspotes in the genone will assort together.
What differentiated femail gametogenesis from male gametogensis?
One primary Oocyte that enters meiosis will yield one mature gamete and three polar bodies.
Meiosis 1 and Meiosis 2 are both asymmetrical divisions.
What is the progression of a mature gamete in the male meiosis?
- Spermatagonium undergo mitotic expansion
- Primary spermatocytes (2n) enter meiosis 1
- Secondary spermatocytes (2n) enter Meiosis 2 and yield 4 (1n) spermatids
- Spermatids (1n) mature into 4 mature spermatazoa
When does male meiosis begin? How long does it continue?
Are any cells constantly active?
Puberty, continues throughout life
Yes there is a meiotic pool that is constantly dividing and offers many opportunities for mutation.
What phase are germ cells arrested in during femail meiosis?
Prophase 1
At Ovulation what happens to the arrested ooycyte? At what rate are they released?
Do women ever run out of germ cells?
Each oocyte resumes meiosis at the time of ovulation. This presents an age related risk of abnormal chromosome segregtation .
One Per month
Yes at menopause there will be a depletion of oocytes.
What is an evolutionary result of linkage disequlibrium?
Linkage disequlibrium allows haplotype to be evolutionary conserved. Since the genes are in such close proximity they are rarely distributed during recombination.
What is nondisjunction and when does it occure?
An error in chromosome segregation leading to an abnormal chromosome number in one or more daughter cells.
May occur in either mitosis or meiosis.
What are some of the results of nondisjunction?
Name 2
When can they occure?
- Missing Chromosome- results in a monosomy (n=45)
- Extra chromosome- results in a trisomy (n=46)
**They can occure at any time in the cell cycle. **
How many chromosomes are typically involved in nondisjunction?
When are women at the greatest risk?
You typically have a nondisjunction event in one chromosome and have 22 normal pairs.
Meiosis 1 and the risk increases exponentially with age
Describe the mutation trend with age for men?
Describe the mutation trend for females?
- As paternal age increases there are increasing number of mutation transmitted in the germ line. 20 year old father = 25 new mutations, 40 year old father = 65 new mutations.
- Mothers contribute 14 mutations regardless of age.
What is a mosaicism?
The presence of two (or more) geneitcally distinct cell lines within one individual
