Chapter 13 - Meiosis

Question 1

Asexual Reproduction

Answer 1

organisms that reproduce to produce offspring that are exact genetic copies of themselves
- Mitosis
- Binary Fission
- Gives rise to a clone; an individually genetically identical to the parent
Changes in DNA can arise however called mutations

Question 2

Sexual Reproduction

Answer 2

two parents give rise to offspring with unique combinations of genes inherited from the two parents
- Mitosis
- Leads to genetic variation however still family resemblance

Question 3

Genes

Answer 3

linked to parents which program specific traits that emerge as we develop into adults

Question 4

Gene Locus

Answer 4

the specific location of a gene along the length of the chromosome

Question 5

Gametes

Answer 5

vehicles that transmit genes from one generation to the other
- E.g. sperm and eggs in human fertilization

• human gametes have half the normal amount of chromosomes(23) as they form with another gamete

Question 6

Homologous Chromosomes

Answer 6

Chromosomes, 1 from each parent, that are paired up with the same length, centromere position and staining pattern
- They both contain genes controlling the same inherited characters
- can have different alleles however

Question 7

Types of chromosomes

Answer 7

Autosome: a chromosome not directly involved in determining sex

Sex Chromosomes: X and Y chromosomes

Question 8

Meiosis

Answer 8

modified cell division in sexually reproducing organisms consisting of two rounds of cell division with only 1 round of DNA replication, resulting in cells with half the number of chromosome sets

- Fertilization and meiosis alternate in sexual life cycles to maintain a constant number of chromosomes in a species from generation to generation

Question 9

Fertliziation:

Answer 9

when a haploid sperm from father fuses with a haploid egg from mother to produce a diploid zygote

Question 10

Allele

Answer 10

different versions of genes at the corresponding loci inherited from a parent

Question 11

Stages of Meiosis

Answer 11

Prophase 1:
- Spindles begin to form, centrosomes move and nuclear envelope breaks down
- Homologus chromosome undergo crossing over
- Microtubules from one pole attach to kinetochores at the centromere of each homolog and move towards the metaphase plate

Metaphase 1:
- Pairs of homolog chromosomes are arranged at the metaphase plate attached to kinetochores from a pole
○ Line up in independent assorted

Anaphase 1:
- Homologs separate due to breakdown of proteins responsible for sister chromatid cohesion along the arms however cohesion at the centromere persists
- Homolgs are guided to opposite poles

Telophase 1 and Cytokinesis:
- Each half of a cell contains a haploid set of duplicated chromosomes
- Cytokinesis occurs simultaneously with a cleavage furrow forming and creating two daughter cells

Prophase 2:
- A spindle apparatus forms
- Chromosomes with two chromatids at the centromere are moved by microtubules towards the metaphase plate

Metaphase 2:
- Having been positioned at the metaphase plate, the kinetochores of sister chromatids are attached to microtubules
- the crossing over in meiosis 1 means that the two chromatids are not genetically identical

Anaphase 2:
- Chromatids separate and move towards opposite poles due to the breakdown of proteins holding sister chromatids at centromere
- Creates individual chromosomes

Telophase 2 and Cytokinesis:
- Nuclei form, chromosomes decondense and cytokinesis occurs
○ Another two daughter cells form creating 4 haploid cells in total which are all genetically distinct from the parent cell

Question 12

the 3 unique events of Meiosis occurring in Meiosis 1

Answer 12

• Homologous Chromosome synapsis and Crossing over in prophase 1
  • Formation of tetraheds in metaphase 1
  • Homologous chromosomes separating at anaphase 1

Question 13

Crossing Over Process

Answer 13

1. After interphase, each pair of homologs associate along their length and DNA molecules are two nonsister chromatids are broken at precisely corresponding points
   2. The synaptonemal complex(zipper like) begins to form and attaches one homolog to the other as chromatins begin to condense
   3. The synaptonemal complex is fully formed with the two homologs being in synapsis; the DNA breaks are closed up creating crossover
   4. After the synaptonemal complex disassembles, the homologs move slightly apart but remain in contact due to crossover; known as chiasmata
2. what is left are recombinant chromosomes which carry genes from two parents

Question 14

Mechanism involved in creating Genetic Variation from Sexual Reproduction

Answer 14

• Independent Assortment of Chromosomes: the random chance of how chromosomes line up at the metaphase plate in metaphase 1 of meiosis.
  • Crossing Over: chromosomes holding a combination of paternal and maternal genes
  • Random Fertilization: millions of zygotic combinations
    • mutation:

Question 15

Evolutionary Significance of Genetic Variation in Populations

Answer 15

• Darwin recognized that population evolves through differential reproductive success of its variant members
  
  • Those individuals better suited to the local environment leave the most offspring, therefore transmitting their genes
    • Natural selection results in the accumulation of genetic variations favored in a certain environment