Meiosis & Sexual

Reproduction

Lecture 11

________

Transfer of characteristics from parent to

offspring through their

genes

• ________ - Complete complement of an organism’s DNA.

• ___________ - carry genes.

• ______ – “unit of heredity” made of DNA.

Chromosomes & Genes

• Cellular DNA is organized in ______________.

• ______ have specific places on chromosomes.

HomologuesChromosomes exist in homologous pairs in ______

(2n) cells.

Exception: Sex chromosomes (X, Y).

Other chromosomes, known as ___________, they have homologues.

Diploid organisms receive one of each type of chromosome from female parent (maternal chromosomes) and one of each type of chromosome from male parent (paternal chromosomes)

A “matched” pair of maternal andpaternal chromosomes are called___________.

Ploidy – refers to the number of sets of homologous chromosomes in cells● haploid – one copy of each chromosome – designated as “n” (gametes)

● diploid – two copies (= pair) of each chromosome – designated as “2n” (somatic cells)

Karyotype• A karyotype is the complete set of

all chromosomes of a cell of any living organism.

• The chromosomes are arranged and displayed (often on a photo) in a standard format: in pairs, ordered by size.

• Upper right is a typical karyotype of a human male.

• Center is a karyotype showing duplicated homologous chromosomes.

• Lower right is a karyotype of a human sperm.

__________ Reproduction

– Many single-celled organisms reproduce by splitting, budding.

– Some multicellular organisms can reproduce asexually, produce _____ (offspring genetically identical to parent).

– Type of cell division?

_______ Reproduction

• Fusion of two ________ to produce a single zygote.

• Introduces greater genetic variation, allows genetic recombination.

• With exception of self-fertilizing organisms, zygote has gametes from two different parents.

Peter + Lois = Stewie

In humans …

• At fertilization, 23 chromosomes are donated by each parent. (total = 46 or 23 pairs).

• Gametes (sperm/ova):– Contain 22 autosomes and 1 sex chromosome.– Are haploid (haploid number “n” = 23 in humans).

• Fertilization results in diploid zygote.– Diploid cell; 2n = 46. (n = 23 in humans)

• Most cells in the body are produced by _________.

• Only gametes are produced by _________.

Mitosis vs. Meiosis

• 2n

• Clone

• Same genetic information in parent cell and daughter cell.

• Give me another one just like the other one!

• 1n

• Daughter cells different from parent cell and from each other.

• Daughter cells have ½ the number of chromosomes as somatic cell.

• Shuffling the genes(Mix it up!)

Meiosis - Sex Cell (Gamete) Formation

In meiosis, there are 2 divisions

of the nucleus:

meiosis I &

meiosis II

http://www.sumanasinc.com/webcontent/animations/content/meiosis.html

http://www.johnkyrk.com/meiosis.html

Meiosis Animations:

http://www.sumanasinc.com/webcontent/animations/content/meiosis.html

http://www.johnkyrk.com/meiosis.html

Meiosis Animations:

Mitosis vs. Meiosis

Meiosis creates genetic variation

_________• During normal cell growth, mitosis produces daughter

cells identical to parent cell (2n to 2n)

__________• Results in genetic variation by shuffling of maternal

and paternal chromosomes.

• No daughter cells formed during meiosis are genetically identical to either mother or father.

• During sexual reproduction, fusion of the unique haploid gametes produces truly unique offspring.

How is this “shuffling” accomplished?

Genetic shuffling of Meiosis 1

1. Crossing over in Prophase I

2. Independent assortment in Metaphase I.

_______ ______You will also see the terms “synapsis” & “chaisma” associated with this process.

Homologues break at identical locations, then rejoin opposite partners.

This creates new combinations of the alleles on each chromosome.

Occurs randomly several times on every chromosome.

Results in mixing of the genes you inherited from your parents.

Crossing over_________ is the pairing of two homologous chromosomes that occurs during meiosis.

_________ are the sites of crossing over.

Exchange of genetic material between non-sister chromatids.

Crossing over produces recombinant chromosomes.

__________ _________

Meiosis & Sexual Life Cycle

• _____ ______ = sequence of stages in organisms reproductive history; conception to reproduction.

• ________ cells = any cell other than gametes, most of the cells in the body.

• _________ produced by meiosis.

Meiosis Practicing

Each kit should have:- 6 duplicated chromosomes (3 sets of

homologues)

- 4 pieces of string

BEFORE you start writing and doing your Meiosis Worksheet, make sure that you have modeled the stages of Meiosis with the chromosome kits. (If your group needs help, raise your hand & I will come over assist.)