Meiosis Flashcards
Consists of 2 major phases:
- M. phase
- Interphase
Cell Cycle
Mitotic phase: cell division
M phase
Chromosomes are being replicated in preparation for cell division
Interphase
Consists of G1, S, and G2 phases
Interphase
Each chromosome is composed of a single chromatid, containing 1 DNA molecule
G1 (gap) phase
Each chromatid is replicated so that each chromosome contains two identical DNA molecules, called sister chromatids
S (synthesis) phase
Each chromosome now consists of two sister chromatids
G (Gap 2) phase
After S phase, how many copies of each gene would you have in an organism that is normally diploid?
4
In an individual who is heterozygous at a locus, how many copies of each allele would you find following S phase?
2
Are sister chromatids identical?
Yes
Are homologous chromosomes identical?
No
Two successive divisions of a cell after only one round of DNA replication
Meiosis
Formation of haploid gametes in animals
Gametogenesis
Formation of haploid spores in plants and fungi
Sporogenesis
Prior to meiosis, DNA replicates during ____ phase by way of the replication processes we have already discussed.
S
Chromosomes condense; synapse formation
-2n
Prophase I
Independent assortment; line up along metaphase plate
Metaphase I
Separation of homologous chromosomes
Anaphase I
Crossing over occurs during _____?
Prophase I
Produce new allele combinations in a chromatid
Genetic recombination
Cross-like structure where crossing over occurs
Chiasma
Two chromosomes pared up; align according to areas of homology
Synapse
Homologous pair of chromosomes each with 2 sister chromatids
Tetrad
Genetic significance of Meiosis
- Each gamete at the end of meiosis carries only one copy of each chromosome
- In meiosis I, homologous chromosomes end up at one pole or the other at random
- In meiosis I, chromosomes don’t influence each other’s segregation
- Crossing over between maternal and paternal homologs during meiosis I creates new allele combinations
Crosses between true-breeding strains of peas with alternative forms of a single trait; genotype peas had was homozygous; each diploid organism can have up to 2 alleles for each gene
Mendel’s Law of Segregation monohybrid crosses
Masking of traits
Dominance
Different alleles arise through______.
Mutations
Loss of function mutation and gain of function mutation
How dominance occurs at the molecular level
Principle of Segregation
- Recessive traits, which are masked in the F1 generation, reappear in the specific proportion of the F2
- Two alleles segregate from each other during the formation of the gametes in anaphase I in meiosis
- Half of gametes get one allele, other half get other allele
- Then the union of gametes is random
Cross of unknown genotype possessing the dominant phenotype with a known homozygous recessive individual (tester)
Testcross
Test to know if an individual with a dominant phenotype is homozygous or heterozygous.
Testcross
All progeny from testcross show the dominant phenotype
Unknown is homozygous
Progeny from testcross show approximately 1:1 dominant to recessive phenotype
Unknown is heterozygous
If a mous has a dominant phenotype (P-), how would you determine if it is homozygous (PP) or heterozygous (Pp)?
a. Cross it to a homozygous dominant mouse
b. Cross it to a mouse with the dominant trait but a similarly unknown genotype
c. Cross it to a mouse with the recessive trait
D. Cross it to a heterozygous dominant mouse
E. It cannot be determinded
c. Cross it to a mouse with the recessive trait
Principle of Independent Assortment
- The two causative genes for two pairs of traits assort independently of one another
- Pairs of alleles for genes on different chromosomes segregate independently in the formation of gametes during meiosis
- Line up along metaphase plate is random
* Chromosomes pull apart separately from one another
How meiosis explains independent assortment
How many different types of gametes can be formed by the genotype AaBbCc?
a. 3
b. 4
c. 8
d. 16
e. 32
c. 8
The probability of two independent events occurring simultaneously is the product of their individual probabilities
-“and”
Product Rule
The probability of either one of several independent, mutually exclusive events is the sum of their individual probabilities
-“or”
Sum Rule
The probability that a situation will occur when there are multiple ways to get a combination
Binomial theorem
Dominant Human diseases that follow Mendelian inheritance
- Achondroplastic dwarfism: caused by interference by interference in bone development; gain of function mutation
- Huntington’s disease: loss of function mutation
Recessive Human diseases that follow Mendelian inheritance
- Caused by loss of function mutation
- Albinism
- PKU: Missing enzyme that breaks down phenylalaine
- Cystic Fibrosis
- Tay Sachs
- Sickle Cell Anemia
Pedigree Symbols: 1. Circle 2. Square 3. Diamond 4. Shaded symbol 5. Double bonded line between symbols 6. Single bonded line between M and F 7. Branched connection between symbols 8. Proband 9. Slash through symbol 10 .Dot in symbol 11. Roman Numerals
- Female
- Male
- Unknown sex
- Affected individual
- Consanguineous parents (related)-up to 2nd cousins
- Parents (unrelated)
- Siblings
- Patient, person of interest
- Deceased individual(s)
- Heterozygous carrier
- Succesive generations
Mode of inheritance where in a pedigree, a generation was skipped and then the dominant trait came back.
Recessive
Mode of inheritance where in a pedigree, the affected patients in each generation are not sex-linked and it appears in a 50% chance in each generation.
Dominant autosomal
