Honors

Biology

Ch. 10

Honors

Biology

Ch. 10

Sexual Reproduction and Genetics

Sexual Reproduction and Genetics

- one member of a pair comes from each parent

I. MeiosisI. MeiosisA. Homologous Chromosomes:

- pairs of chromosomes that are very similar

B. Diploid:B. Diploid:- a full set of homologous

chromosomes (2n)- in humans: 46 (23 pairs)- in pea plants: 14 (7 pairs)

Human Chromosomes

(23 homologous pairs)

Human Chromosomes

(23 homologous pairs)

C. Haploid:C. Haploid:- a half set of chromosomes (1n)- occur in Gametes (specialized

reproductive cells: sperm and egg)

D.Process of Meiosis:D.Process of Meiosis:- specialized cell division in which the

chromosome number is cut in half- homologous pairs of chromosomes are

separated- produces haploid gametes- occurs in 2 stages:

1.Meiosis I:1.Meiosis I:a) similar to mitosis, but, during

metaphase, homologous chromosomes come together to form a tetrad

b) Crossing-over occurs: exchange of genes between homologous chromosomes

c) The homologous chromosomes separate during anaphase I.

c) 2 cells are produced that contain 1 replicated chromosome from each homologous pair.

Meiosis IMeiosis IHomologous chromosome

s pair and cross over

Homologous chromosomes exchange DNA

& align on equator

Homologous chromosomes

move to opposite

poles

Prophase I IProphase I IMetaphase IMetaphase I Anaphase IAnaphase I Telophase ITelophase I

red

red

Purple

Purple

round

round

Long

Long

PP

PP

pp

pp

LL

LL

ll

ll

PP

pp

pp

LL

LL

ll

ll

PP

LL

pp LL

ll

ll

PP

pp

PP

LL

pp LL

ll

ll

PP

pp

LL

LL

ll

ll

PP

PP

pp

pp

PP

PP

pp

pp

LL

LL

ll

ll

PP

pp

pp

LL

LL

ll

ll

Crossing Crossing OverOver

Crossing Crossing OverOver

SisterSisterChromatidsChromatids

ReplicatedReplicatedChromosomeChromosome

ReplicatedReplicatedChromosomeChromosome

LL

LL

ll

ll

PP

PP

pp

pp

SisterSisterChromatidsChromatids

Homologous

Homologous

Chromosomes

Chromosomes

PP

PP

pp

pp

LL

LL

ll

ll

PP

pp

pp

LL

LL

ll

ll

pp LL

PP ll

LLPP

llpp

old combinationold combination

new combinationnew combination

new combinationnew combination

old combinationold combination

FlowerColor

PollenShape

ChiasmataChiasmata

Crossing-over in a tetrad of a grasshopper.

Each cross-over is called a chiasma. This example shows 5 chiasmata.

2.Meiosis II:2.Meiosis II:a) similar to mitosis but DNA replication

does not occur before divisionb) Sister chromatids separate during

anaphase II.c) 4 haploid daughter cells are produced

Meiosis IIMeiosis II

Prophase IIProphase II

Metaphase IIMetaphase II

Anaphase IIAnaphase II

Telophase IITelophase II

FourHaploid

Cells

FourHaploid

Cells

SpermatogenesisSpermatogenesis OogenesisOogenesis

SpermatogoniaSpermatogonia

Primary Spermatocyt

e

Primary Spermatocyt

e

Secondary Spermatocyt

es

Secondary Spermatocyt

es

SpermatidsSpermatids

Spermatozoa

Spermatozoa

Primordial Germ Cells

Primordial Germ Cells

Mitosis

Meiosis

Meiosis

Oogonia

Oogonia

Primary Oocyte

Primary Oocyte

Secondary Oocyte & Polar Body

Secondary Oocyte & Polar Body

Ovum & Polar Body

Ovum & Polar Body

Unequal division of cytoplasm produces oocytes and polar

bodies.

E. Importance of Meiosis:E. Importance of Meiosis:- provides genetic variation in the next

generation

1.1. Independent AssortmentIndependent Assortment- chromosomes randomly separate

during meiosis- results in gametes with different

combinations of chromosomes- for pea plants, 27 = 128 different

combinations

The Independent Assortment of Homologous Chromosomes in

Meiosis

The Independent Assortment of Homologous Chromosomes in

Meiosis

Key

Maternal set ofchromosomes

Paternal set ofchromosomes

Possibility 1

Two equally probable arrangements ofchromosomes at

metaphase I

Possibility 2

Metaphase II

Daughtercells

Combination 1 Combination 2 Combination 3 Combination 4

2. Crossing over2. Crossing over- produces recombined chromosomes

that carry genes derived from two different parents

The Results of Crossing over During

Meiosis

The Results of Crossing over During

MeiosisProphase Iof meiosis

Nonsisterchromatids

Tetrad

Chiasma,site ofcrossingover

Metaphase I

Metaphase II

Daughtercells

Recombinantchromosomes

3. Random Fertilization3. Random Fertilization- combines chromosomes from 2

parents- results in over 70 trillion possible

combinations of genes from any 2 parents

IIII.. Mendel’sMendel’s LawsLaws ofof

HeredityHeredityIIII.. Mendel’sMendel’s LawsLaws ofof

HeredityHeredityHeredity:- the passing of traits from parent

to offspring

Genetics:- the study of heredity

Early Idea about GeneticsEarly Idea about Genetics

HomunculusHomunculus

A. Gregor Mendel:A. Gregor Mendel:- father of genetics - Austrian monk - developed the

basic principles of Heredity

(1880's)

B. Mendel’s ExperimentsB. Mendel’s Experiments

1. Used garden peas- several crops

per year- small, fast

growing- developed

"purebreds"

- easy to control pollinate

Pea Pea FlowerFlower

Pea Pea FlowerFlower

StamensStamens(male)(male)

produceproducepollenpollen

StamensStamens(male)(male)

produceproducepollenpollen

PistilPistil(female)(female)producesproduces

eggseggs

PistilPistil(female)(female)producesproduces

eggseggs

- seven distinct, inherited traits

Plant size

Flower location

Flower color

Pod color

Pod shape

Seed shape

Seed color

2. Used math and statistics to support theories

3. Published results in 1859- rejected by academic peers- in 1900 his work was rediscovered

P F1

F1 F2

III. Principles of Heredity

III. Principles of Heredity

A.Concept of Unit

Characters:- traits are controlled by "factors" (genes) which occur in pairs- one from each parent

B. Principle of Dominance

and Recessiveness:

B. Principle of Dominance

and Recessiveness:- some alleles dominate, or mask, the

effect of other alleles- Allele: one of the "versions" of a gene

C.Law of Segregation:C.Law of Segregation:- during meiosis (production of

gametes), each pair of genes separate

Cross Fertilization of Parents

Cross Fertilization of Parents

Purebred (Homozygous)

Purple-floweredParent

Purebred (Homozygous

) White-floweredParent

Cross-FertilizeCross-Fertilize

All Purple-flowered

(Heterozygous) Offspring

Pollen

PollenPPPP pppp

PP ppPpPp

F1

Self-FertilizeSelf-Fertilize

F2 F2 F2 F2

75% Purple75% Purple25% White25% White

Self-fertilization of F2

PpPp

PPPP PpPp PpPp pppp

1. Gametes:1. Gametes:- specialized, reproductive cells (sperm, egg)- have 1/2 a set of chromosomes

1. Gametes:

2. Genotype:- genetic make-up of an organism

3. Phenotype:- physical appearance of an organism

- specialized, reproductive cells(sperm, egg)

- have 1/2 a set of chromosomes

4. Homozygous: - alleles in a gene pair

that are identical- TT or tt

TT Tt tt

5. Heterozygous: - alleles in a gene

pair that are different

- Tt

D.Principle of Independent Assortment:

D.Principle of Independent Assortment:- alleles separate randomly during

meiosis

IV. Applying Mendel‘s Principles

IV. Applying Mendel‘s Principles

A.Probability:- the likelihood that an event may happen

B.B.Rules of Probability:Rules of Probability:B.B.Rules of Probability:Rules of Probability:1.Product Rule of

Probability:- when events occur in combination, the probability of each event is multiplied by the probability of the other

1/2 x 1/2 x 1/2 = 1/8

What are the odds of rolling 3 tails in a row?

Cystic Fibrosis F = Normalf = cystic fibrosis

1 out of 25 are heterozygous in UK

Odds of any heterozygous man and woman

marrying =

1/25 x 1/25 =

Odds of a heterozygous man and woman

having a child with cystic fibrosis =

1/625 x 1/4 =

2.2. Probability has No Memory:Probability has No Memory:2.2. Probability has No Memory:Probability has No Memory:- Previous events do not influence the

probability of future events

What are the odds on the next toss being a tail?

1/2

The odds of rolling 3 tails in a row are 1/8.

V. Gene Linkage and PolyploidyV. Gene Linkage and PolyploidyA. Gene Linkage

- Chromosomes contain thousands of genes.- Genes are physically linked together on a chromosome.- During crossing over this linkage can be broken temporarily.- Frequency of crossing over can be used to make chromosome maps.

V. Gene Linkage and PolyploidyV. Gene Linkage and PolyploidyA. Gene Linkage

V. Gene Linkage and

PolyploidyV. Gene Linkage and

PolyploidyA. Gene Linkage

B. PolyploidyB. Polyploidy- The occurrence

of one or more extra sets of all

chromosomes in an organism.

B. PolyploidyB. Polyploidy- The occurrence of one or more

extra sets of all chromosomes in an organism.

- Rare in animals but occurs commonly in plants.

- Produces new plant varieties

Coffee beans, 4n = 44

Banana, 3n = 33

Cotton, 4n = 52

Potatoes, 4n = 48

Corn, 4n = 20

Canola oil, 4n = 38

Bread wheat, 6n = 42

Rope from sisal, 5n = 180

A Sample of Agricultural

Crops That Are Polyploid

A Sample of Agricultural

Crops That Are Polyploid

The Evolution of Wheat

The EndThe End

3. When an event can happen in more than one combination, the probability of the event is the sum of the probability of each.

OR

1/4

What are the odds of getting ‘a head and a tail’

any order?

+ 1/4= 1/2