Meiosis and Sexual Life Cycles

Question 1

What does heredity mean?

Answer 1

Transmission of traits from one generation to the next

Question 2

What does variation mean?

Answer 2

It’s differences between members of a species

Question 3

What is genetics?

Answer 3

Scientific study of heredity and hereditary variation

Question 4

What is a gene?

Answer 4

A stretch of DNA encoding a specific RNA or protein

Question 5

Locus (loci)

Answer 5

The specific location of a gene on a chromosome

Question 6

What is asexual reproduction?

Answer 6

• Single parents produces offspring with identical genomes
• Mitosis

Question 7

What is sexual reproduction?

Answer 7

• Parents produce offspring with unique gene combinations
• Involves meiosis and fertilization
• Produces genetic variation

Question 8

What are gametes?

Answer 8

Reproductive cells

Question 9

What are somatic cells?

Answer 9

Any body cell except sperm or egg cells

Question 10

How many copies of each chromosome do somatic cells have?

Answer 10

• Two copies
• Diploid

Question 11

How many copies of each chromosome do gamete cells have?

Answer 11

• One copy each
• Haploid

Question 12

What are homologous chromosomes?

Answer 12

• Chromosomes with the same genes at the same loci
• May carry different alleles

Question 13

Karyotype

Answer 13

A display of the chromosome pairs of a cell arranged by size and shape

Question 14

How many pairs of chromosomes do humans have?

Answer 14

• 23 pairs
• 22 pairs of autosomes and 1 pair of sex chromosomes

Question 15

Sexual life cycle - animals

Answer 15

• Gametes are the only haploid cells
• A zygote divides through mitosis to grow into a multicellular adult human
• Adult human germ cells (2n) produce gametes (n) through meiosis

Question 16

What is fertilization?

Answer 16

Gametes (n) join and their nuclei fuse, producing a zygote (2n)

Question 17

Sexual life cycles - plants and some algae

Answer 17

• Meiosis produces haploid spores that undergo mitosis to produce a multi-cellular haploid organism
• Gametes are produced by mitosis
• Fertilization produces a diploid zygote that undergoes mitosis to produce a multicellular diploid organism

Question 18

What is the alternation of generations?

Answer 18

Includes both diploid and haploid stages that are multicellular

Question 19

Sexual life cycles - most fungi and some protists

Answer 19

• Fertilization produces a unicellular diploid zygotę that undergoes mitosis to produce haploid cells
• Haploid cells then undergo mitosis to produce unicellular descendants or a multi-cellular haploid organism
• Gametes are produced from haploid cells via mitosis

Question 20

Meiosis Overview

Answer 20

• Producing haploid cells from diploid cells, involves 2 rounds of cell divisions but one round of DNA replication
• 4 haploid cells are produced from 1 diploid cell

Question 21

Meiosis I - Prophase I

Answer 21

• Chromosomes condense
• Spindle forms
• Nuclear envelope breaks down
• Crossing over occurs
• Kinetochore forms
• Microtubules attach
• Non-sister chromatid break at points, and homologues held together by the synaptonemal complex in a process called synapsis

Question 22

What is crossing over?

Answer 22

• exchange of DNA between non-sister chromatid during prophase I
• increases genetic variability

Question 23

What is synapsis?

Answer 23

The fusion of chromosomes pairs at the start of meiosis

Question 24

What is chiasma

Answer 24

• point of contact between non sister chromatids

Question 25

Meiosis I - Metaphase I

Answer 25

homologous chromosome pairs align at metaphase plate

Question 26

Meiosis I - Anaphase I

Answer 26

• Cohesions breakdown along chromosome arms
• Homologous chromosomes move to opposite poles

Question 27

Meiosis I - Telophase I and cytokinesis

Answer 27

• Forms two haploid cells
• Each chromosome still consists of two sister chromatid

Question 28

Meiosis II Overview

Answer 28

• Equivalent to mitosis, ister chromatids split but they are not genetically identical
• Each haploid cell from meiosis I produces two haploid cells

Question 29

Meiosis II - Prophase II

Answer 29

• mitotic spindle starts to form
• nuclear envelope fragments
• kinetochore forms
• microtubules attach

Question 30

Meiosis II - Metaphase II

Answer 30

chromosomes align at metaphase plate

Question 31

Meiosis II - Anaphase II

Answer 31

• cohesion sprung centromere cleaved
• sister chromatid separate
• cell elongates

Question 32

Meiosis II - Telophase II and cytokinesis

Answer 32

• nuclei form
• cells split
• product is 4 haploid cells

Question 33

What events are unique to meiosis?

Answer 33

• Synapsis and crossing over
• Alignment and separation of homologous chromosomes

Question 34

What is the main advantage of sexual reproduction?

Answer 34

The new combinations of alleles

Question 35

What are the 3 factors that contribute to genetic variability?

Answer 35

1. Independent assortment of chromosomes
2. Random fertilization
3. Crossing over

Question 36

What is independent assortment of chromosomes?

Answer 36

• alignment of each pair of homologues is independent of other pairs of homologues 2^n possibilities
• where n = number of pairs of chromosomes

Question 37

What is random fertilization?

Answer 37

• any sperm and egg can fuse to produce a zygote
• 2^n * 2^n possibilities

Question 38

What is crossing over?

Answer 38

• produces recombinant chromosomes with unique set of alleles
• in humans 1-3 crossovers per chromosome