Meiosis

Question 1

Gene

Answer 1

Units of heredity, made up of segments of DNA

Question 2

Allele

Answer 2

Different versions of genes

Question 3

Locus

Answer 3

Specific location of gene

Question 4

Gametic Cell (Gametes)

Answer 4

Genes are passes to the next generation through gametes (sperm and egg)
Haploid
Produced by meiosis

Question 5

Diploid Zygote

Answer 5

Fertilized egg, has one set of chromosomes from each parent (2 sets in total)

Question 6

Somatic Cells

Answer 6

Produced by zygote by mitosis and develops into an adult organism
All other cells in body excluding sperm and egg
Diploid

Question 7

Which parts of the human sexual life cycle is haploid and diploid

Answer 7

Diploid - ovary and testis to meiosis, after fertilization (mitosis and development)
Haploid - meiosis to egg and sperm to fertilization

Question 8

Homologous chromosomes (homologs)

Answer 8

The 2 chromosomes in each pair
Can exist un-replicated or replicated
Same size, have genes which are arranged in same order

Question 9

Karyotype

Answer 9

An ordered display of chromosomes of an individual cell

Question 10

What is the purpose of adding colchicine during karyotype preparation

Answer 10

Arrests the cell at the metaphase during cell division, so its easier to locate chromosomes and extract them out for the karyotype
At metaphase the chromosomes are the most condensed (lined up in the middle)

Question 11

How many chromosomes are found in human haploid cells (gametes) and human diploid cells (somatic cells)
How many autosomes and sex chromosomes in the number of chromosomes?

Answer 11

Human diploid cell (somatic cell) - 46, 2 sets of 23
22 pairs are autosome (don’t determine sex)
23rd pair is sex chromosomes
Human haploid cell (gametes) - 23, 22 autosomes, 1 sex

Question 12

Reductional division (meiosis l) versus Equational division (meiosis ll)

Answer 12

Reductional division - diploid parent cell results in 2 haploid daughter cells
Equational division - 4 haploid daughter cells with unreplicated chromosomes

Question 13

What steps are associated with meiosis l and meiosis ll

Answer 13

Meiosis l - prophase 1, metaphase 1, anaphase 1, telophase 1 and cytokinesis
Meiosis ll- prophase 2, metaphase 2, anaphase 2, telophase 2 and cytokinesis

Question 14

Synapsis

Answer 14

Homologous replicated chromosomes loosely pair up, aligned gene by gene

Question 15

Bivalent

Answer 15

Pair of homologs
Each bivalent has one or more chiasmata

Question 16

Crossing over

Answer 16

Non-sister chromatids exchange DNA segments to produce chromosomes with a combination of maternal and paternal alleles

Question 17

Chiasmata in Prophase l

Answer 17

Chiasmata - regions where crossing over occurs

Question 18

Centrosome

Answer 18

Organelle that serves as microtubule organizing center
Replication lead to 2 centrosomes that migrate opposite ends of cell

Question 19

Asters

Answer 19

A radial array of short microtubules that extend from each centrosome, help to anchor centrosome

Question 20

Spindle microtubules (kinetochore and non-kinetochore (or polar) microtubules)

Answer 20

Kinetochore - capture chromosomes by binding to kinetochore proteins
Non-kinetochore - (polar microtubules) do not capture chromosomes

Question 21

In addition to mutations, list 3 other mechanisms that contribute to genetic variation in humans

Answer 21

Independent assortment of chromosomes -homologous pairs of replicated chromosomes (bivalents) orient randomly at metaphase 1
Crossing over - produces recombinant chromosomes, which combine genes inherited from each parent, begins at prophase 1, combines DNA from 2 parents into a single chromosome
Random fertilization - Any sperm can fuse with any ovum(unfertilized egg)

Question 22

Chromosomal Disorders
examples?

Answer 22

Down syndrome - due to 3 copies of chromosome 21
Klinefelter syndrome - an XXY male (individual has male sex organs but are sterile)
Turner syndrome - an XO female (do not mature sexually during puberty, sterile) missing a chromosome

Question 23

Stages of Meiosis l
What occurs in each stage

Answer 23

Prophase 1 - replicated chromosomes condense and spindle microtubules begin to form centrosomes (diploid)
Metaphase 1 - paired homologs line up at metaphase plate at random (diploid)
Anaphase 1 - paired homologs sperate (diploid), chromosomes move guided by spindle microtubules
Telophase 1- homologs finish migrating to the poles of the cell (diploid)
Cytokinesis - forming 2 haploid daughter cells

Question 24

Stages of Meiosis ll
What occurs in each stage

Answer 24

Prophase 2 - spindle microtubules form, replicated chromosomes (composed of 2 sister chromatids) move toward metaphase plate (no synapsis, chiasmata, crossing over)
Metaphase 2 - replicated chromosomes arranged at metaphase plate (due to cross over in meiosis 1, 2 sister chromatids no loner genetically identical
Anaphase 2 - sister chromatids separate, move as individual chromosomes to opposite poles of cell (un-replicated chromosomes)
Telophase 2 - chromosomes (un-replicated) arrive at opposite poles, nuclei form, chromosomes begin decondensing
Cytokinesis - 4 daughter cells, each have haploid set of un-replicated chromosomes, cell is genetically distinct