Biology Unit 5 Topic 1-2: Meiosis & Meiosis and Genetic Diversity

heredity

transmission of traits from one generation to the next

genes

segments of DNA that code for basic units of heredity and offspring acquires it from parents by inheriting chromosomes

mutations

the only source of variation of chromosomes in asexual reproduction

homologous chromosomes

a pair of chromosomes (same size, length, centromere position) that carry the same genetic info

characteristics of asexual reproduction

1 individual

no fusion of gametes

offspring are exact copies (clones)

mutations are only source of variation

done through mitosis

characteristics of sexual reproduction

2 parents

offspring are unique combinations of genes from parents

genetically varied from parents and siblings

karyotype

a display of chromosome pairs ordered by size and length

somatic cell

body cells that are diploid (2n)

mitosis occurs here

gametic cell

sex cells (eggs and sperm)

haploid (n)

formed by meiosis

diploid

2n

two complete sets of each chromosome

haploid

n

one set of each chromosome

autosome

chromosomes that do not determine sex

humans have 22

sex chromosome

chromosomes that determine sex

called X and Y

includes eggs (X) and sperm (X or Y)

life cycle

sequence of takes in the reproduction history of an organism rom conception to its own reproduction

zygote

a diploid somatic cell formed through fertilization when a sperm cell fuses with an egg

genetics

the branch of biology that studies heredity and various organisms

clones

offspring that are exact copies of its parent

meiosis

a process that creates haploid gamete cells in sexual reproductions diploid organisms

results in daughter cells with half the number of chromosomes as the parent cell

involves two rounds of division

How are traits passed from parents to offspring?

genes

differences between mitosis and meiosis

mitosis-occurs in somatic cells, 1 division, results in 2 diploid daughter cells, daughter cells are genetically identical

meiosis-forms in gametes, 2 divisions, results in 4 haploid daughter cells, each daughter cells is genetically unique

similarities between mitosis and meiosis

cell division, same stages of division; requires interphase to organize DNA

If meiosis halves the numbers of chromosomes in gametes, then how do the cells return to normal chromosome number (i.e. how do somatic cells stem from these gametic cells)?

through fertilization when a sperm cell fuses w/ an egg to form a diploid cell

If an organism is 2n=24 what is their haploid number?

n=12

How many cells does meiosis start with? How many does it end with?

starts w/ diploid cells; in humans: 46

ends w/ haploid cells; in humans: 23

If the eggs of Drosophila have two chromosomes, how many chromosomes do their diploid cell contain?

4 chromosomes

synapsis

in prophase I

homologous chromosomes pair up and physically connect to each other forming a tetrad

tetrad

structure formed by the pairing of homologous chromosomes

consist of four sister chromatids

chiasmata

points of contact or crossover between non-sister chromatids of homologous chromosomes during crossover

crossing over

(recombination) occurs at the chiasmata and DNA is exchanged between the homologous pairs

independent assortment

in metaphase i

process of tetrad lining up at the metaphase plate in a unique way

What are the “key events” that happen in meiosis?

meiosis i

interphase: G1, S (DNA is copied), G2

prophase i: synapsis occurs and DNA is exchanged through crossing over

metaphase i: tetrads line up at metaphase plate orienting themselves independently

anaphase i: pairs of homologous chromosomes separate w/ the sister chromosomes still attached

telophase i and cytokinesis: nuclei and cytoplasm divide leaving a haploid set of chromosomes in each daughter cell

meiosis ii

prophase ii: spindle forms

metaphase ii: chromosomes line up at metaphase plate

anaphase ii: sister chromatids separate and move towards opposite poles in both cells

telophase II and cytokinesis: nuclei reappears and 4 genetically unique haploid cells produced

How is it possible that every gamete produced through meiosis has a unique combination of DNA?

crossing over in prophase i and independent assortment in metaphase i

In your own words describe the three ways in which meiosis can lead to genetic variation.

crossing over-chromosomes exchange DNA; makes recombinant chromosomes

independent assortment-chromosomes oriented randomly along metaphase plate; can orient with either maternal or paternal chromosomes closer to given pole

random fertilization-any sperm can fertilize any egg

How are the offspring produced in asexual reproduction different than that of those in sexual reproduction? In terms of agricultural studies, when would it be advantageous to produce an organism through asexual reproduction?

in asexual reproduction they are exact clones but in sexual reproduction they are unique combinations of genes

advantageous when the producer is satisfied with the organism’s characteristics

genetics

study of heredity and hereditary variation

offspring acquire genes from parents by inheriting…

chromosomes

one homologous chromosome is inherited from…

each parent

the two rounds of division in meiosis

meiosis i and meiosis ii

the three key events in meiosis that are unique:

1. prophase i: synapsis and crossing over

2. metaphase i: tetrads (homologous pairs) line up at the metaphase plate

3. anaphase i: homologous pairs separate

if the parent cell begins early meiosis I with 2n=4, the daughter cell will end telophase ii and cytokinesis with n= ?

2

what two processes ensure genetic diversity in sexually reproducing organisms?

meiosis followed by fertilization

Meiosis followed by fertilization also provides genetic variation that plays a role in…

natural selection

meiosis is driven by the interaction of subcellular components and uses ________ which is required for growth and reproduction of living systems.

free energy