Question

1. If the amount of DNA in a somatic cell equals C during G1 of interphase, how much DNA is present in the cell during each phase of mitosis and meiosis? (2pts) Anaphase Telophase Cytokinesis Prophase 20 Metaphase T Mitosis Meiosis 1 Meiosis 2 2 Define the three things that are responsible for genetic variation and explain how they lead to genetic variation (1.5pts)

Answer 1

	Mitosis	Meiosis I	Meiosis II
Prophase	Nuclear membrane, nucleolus disappears. Chromosomes condense and are visible. Centrosomes migrate to opposite poles. Spindle fibers begin to form.	Subdivided into: Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis. During meiosis I-prophase I- homologous chromosomes pair up to form tetrad or bivalents. Crossing over occurs during synapsis: Synapsis is alignment of homologous chromosomes, forming tetrad. Crossing over involves exchange of genetic material between non-sister chromatids. It occurs during prophase of meiosis I.	Chromosomes condenses Spindle fibres form and attach to chromosomes
Metaphase	A diploid number of chromosomes align at the spindle equator during metaphase: diploid numbers of chromosomes are present during mitosis.	Homologous chromosomes align at the spindle equator during metaphase: During meiosis I-metaphase I- spindle fiber attach at the centromeres of the homologous chromosomes. Homologous chromosomes pair and align at cell center or equator.	A haploid number of chromosomes align at the spindle equator during metaphase
Anaphase	Cohesion of spindle fibres break Chromosomes separate, migrate towards pole On-kinetochore fibre lengthen.	Two homologous chromosomes separate	Sister chromatids separate, by moving towards spindle fibers.
Telophase	Results in 2 genetically identical diploid nuclei: In mitosis, the cell divides into two identical cells with identical nuclei.	Results in two genetically diverse haploid nuclei: In meiosis I, after cytokinesis, 2 genetically haploid cells are produced, which enter meiosis II.	Results in 4 genetically diverse haploid nuclei: In meiosis II, after cytokinesis, 4 genetically haploid cells are produced

Answer:

1.

	Prophase	Metaphase	Anaphase	Telophase	Cytokinesis
Mitosis	2C	2C	2C	2C	2C
Meiosis 1	2C	2C	2C	C	C
Meiosis 2	C	C	C	C	C

2.

• Phenotype value is designated as P (describing a trait or phenotype), genetic value or genotype by G, and E is environmental deviation (representing effect of environment and interaction of genotype with environment):

  P = G + E

  Phenotype variation VP = VG +VE

  Genotypic variation (G) further may be influenced by:

  1. Breeding value (A)- measures the effect of genetic makeup on the phenotype.

  When we consider a population, we measure breeding value in terms of evolution of a phenotypic trait, passed to the subsequent generations. The effect on an individual gene, when passed from parental (P), F1, F2 generations and to offspring is considered as additive effect or additive factor.

  Moreover, the change in the allele of the gene, when passed to offspring (determined by the frequency of the gene at different locus), also determines the breeding value. Thus, breeding value is expressed as the average effect (effect on a gene allele measured in terms of locus and generations).

  2. Dominance deviation (D) – measures the effect of gene due to dominance of an allele.

  3. Epistasis (I)- Interaction of non -allelic genes. This factor is influence by the influence of loci on the gene. This value will change, if a single locus controls a gene, or if there is interaction between multiple loci of the gene.

  Epistatic interactions and dominance are non-additive factors.