Mitosis Meiosis and Heredity

Mitosis and Meiosis

Lab Instructor: Kristin Flores

Learning Objectives

• Cell division – Mitosis– Cytokinesis

• Gametogenesis and meiosis

Important terms

• G1, S, and G2 = Interphase• Fertilization – fusion of egg and sperm nuclei• Zygote – fertilized egg • Gametogenesis – formation of gamete• Spermatogenesis and Oogenesis

Cell division

• NUCLEAR DIVISION1. Mitosis: produces two nuclei, both containing identical chromosomes

I. Prophase II. MetaphaseIII. Anaphase IV. Telophase

2. Cytokinesis: divides the cytoplasm; ensures that each new cells contains all the metabolic machinery necessary to sustain life

Cell Cycle

“C” Words (pg 59)

• CHROMATIN- thread like DNA + protein• CHROMOSOME - Coiled/Condensed DNA + protein• SISTER CHROMATIDS - duplicated chromosome• CENTROMERE – holds chromosomes together• CENTROSOME – microtubule organizing center• CENTRIOLE – microtubule being organized

• Centrosomes contain centrioles

• HOMOLOGOUS CHROMOSOMES – similar in size and carry genes for same trait, but different expression

• CYTOKINESIS – cytoplasmic division

Mitosis: Nuclear division

Mitosis: Nuclear division

Onion Root Tip and Whitefish blastula

Meiosis• NUCLEAR REDUCTION

MEIOSIS I: Replication and crossing over occurResults in two cells, both with same number

of chromatids as the parent cell

MEIOSIS II: Divides the cytoplasm and ensures that each

new cells contains all the metabolic machinery necessary to sustain life

Results in four cells, all with half the number of chromosomes as the parent cell

Meiosis: Nuclear reduction

Spermatogenesis• Same basic events as mitosis

• NO interphase between meiosis I and II• Synapsis and crossing over occurs in Prophase I

• For every 1 diploid primary spermatocyte you put in, you get 4 haploid sperm out.

SpermatogenesisSeminiferous tubule

Oogenesis• Same basic events as mitosis

• NO interphase between meiosis I and II• Synapsis and crossing over occur in prophase I

• Arrested in Prophase I until puberty• Once a month, one egg continues to metaphase II where it is again halted• Will only complete meiosis upon fertilization

• For every 1 diploid primary oocyte you put in, you get 1 egg and 2-3 polar bodies• Polar bodies = “dumping grounds”; woman will just reabsorb them

Oogenesis

Meiosis: Nuclear reduction

MITOSIS VS. MEIOSIS

1.Somatic ?

2.Reproductive cells?

3.Chromosome number of the daughter cells

reduced to half compared to that of parents?

4.Chromosome numbers in daughter cells

remains same as that in parents?

5.Spermatogenesis and Oogenesis?Interactive Mitosis Images:

http://jbworld.jbs.st-louis.mo.us/science/resources/mitosis/mitosistut.html

Lab activities

• Prepare onion root squash mount (handout)• Examine mitosis models and whitefish blastula

slides • Examine spermatogenesis on slides

Heredity

Lab Instructor: Kristin Flores

Learning Objectives

• Heredity terms• Mendel’s Laws of Inheritance• Determining genotype using Punnet Squares

and test cross of Drosophila

Meiosis Review• Genetic diversity is produced by recombining

the diploid cell's genetic complement to generate a haploid gamete.

• This diversity depends upon the segregation and assortment of combination of alleles.

• Importantly, diploid organisms can bear recessive alleles of genes that are can be completely masked by the other (usually wild type) allele.

Important Terms

• Genotype- genetic constitution (genes present)• Phenotype- physical expression of genotype• Alleles- alternate forms of a gene that occupy a

given locus.

Important Terms

• Homozygous- identical alleles (FF, aa, BB)

• Heterozygous- both dominant and recessive alleles are present (Ff, Aa, Bb)

• Dominant trait- expressed in heterozygous conditions (Hh, Kk, Bb)

• Recessive trait- expressed only when homozygous recessive (aa, dd, jj)

Mendel’s Laws of Inheritance • Gregor Mendel formulated his "Laws of Inheritance" from his

famous pea experiments.

• "Law of Segregation” - Each organism contains two alleles for each trait, and the alleles segregate during the formation of gametes during meiosis.

• "Law of Independent Assortment" suggests that alleles of each gene separate independently of the other genes.

Determining Genotype

Gamete Genotype

Gamete Genotype

Diploid Genotype

F F FF

F f Ff

f f ff

Example• Purple flowers are dominant

(A) over white flowers (a) Genotype Phenotype

AA Purple

aa White

Aa Purple

Punnet Squares

• Used to determine genotype of offspring• How do we determine genotype of parents?

– One parent is white flower (aa)– One parent is purple flower (Aa or AA)

Punnet Square

a a

A Aa Aa

A Aa Aa

White FlowerPu

rple

Flo

wer

Homozygous dominant = Offspring all purple

Punnet Square

a a

A Aa Aa

a aa aa

White FlowerPu

rple

Flo

wer

Heterozygous dominant = Offspring 50% purple and 50% white

Sex Linked Cross Example

• Yellow Body is recessive mutation carried on X chromosome (Xf)

• We crossed Yellow Body female with wild type male

Punnet Square

XF Y

Xf XfXF XfY

XfXfXF XfY

Wild TypeYe

llow

Bod

y

Offspring: males all Yellow Body, females all wild type

Punnet Square

a a

A Aa Aa

A Aa Aa

Mutated WingN

orm

al W

ing

Offspring all normal wing

Punnet Square

a a

A Aa Aa

a aa aa

Mutated WingN

orm

al W

ing

Offspring 50% normal wing and 50% mutated wing

Test Crosses

• We are using all recessive traits• Flies with these characteristics must be

homozygous recessive (tt)• Mated with wild type flies (Tt or TT)• Determine if wild type parent was Tt or TT

Sex Determination

Female Male

http://berkeley.edu/news/media/releases/2002/07/images/fruitflies.jpg

Lab activities

Drosophila melanogaster– Determine sex and phenotype

• Separate males and females first• Determine phenotype second• Determine genotype of parents