Intro to MeiosisIntro to Meiosis

• ChromatinChromatin• Unwound, stringyUnwound, stringy• In interphaseIn interphase

• ChromatidsChromatids• ½ of a replicated ½ of a replicated

chromosomechromosome• In Prophase, MetaphaseIn Prophase, Metaphase

• ChromosomeChromosome• After the sisters split in After the sisters split in

Anaphase, they are separate Anaphase, they are separate chromosomes (until they chromosomes (until they unwind into chromatin again)unwind into chromatin again)

Let’s look more closely at a Let’s look more closely at a chromosome…chromosome…

• Genes are pieces of chromosomes Genes are pieces of chromosomes that code for a protein/trait. There that code for a protein/trait. There are different versions that create are different versions that create different traits (ex- hair color)different traits (ex- hair color)

HomologuesHomologues

• You have 23 pairs of You have 23 pairs of chromosomes. In each pair you chromosomes. In each pair you received one from your mom and received one from your mom and one from your dad. Each pair is one from your dad. Each pair is similar, but not exactly alike…we similar, but not exactly alike…we call themcall them

•HOMOLOGOUS PAIRSHOMOLOGOUS PAIRSNote that the chromosomes have the gene in the same place, but different versions of it. (one may be for brown hair, one for blonde)

Homologous Homologous ChromosomesChromosomes

• They are similar in size, shape, and They are similar in size, shape, and the genetic traits that they carrythe genetic traits that they carry

• Chromatids are exact Chromatids are exact copies of each other made copies of each other made by replicationby replication

• Homologous pairs are Homologous pairs are similar chromosomes that similar chromosomes that are the result of are the result of fertilizationfertilization

Do NOT confuse these with sister Do NOT confuse these with sister chromatidschromatids

Sister chromatids-exact copies connected

by a centromere

Homologous Pairssimilar copies of a chromosome

One maternal, one paternal

or

1m 1p1m 1m 1p 1p

Boy Karyotype- displays homologous pairs

Replicated chromosomes after “S” phase of interphase

Haploid vs. DiploidHaploid vs. Diploid

• DIPLOID CELLS:DIPLOID CELLS: have two have two versions of each versions of each

chromosome (one from mom chromosome (one from mom AND one from dad) AND one from dad)

• Has the homologous pairsHas the homologous pairs• Somatic cells (body cells)Somatic cells (body cells)• Made by mitosis or fertilizationMade by mitosis or fertilization• ““2n”2n”• In this picture, what is “n”?In this picture, what is “n”?

• n=2n=2

Diploid vs. HaploidDiploid vs. Haploid

• Haploid cells:Haploid cells: Have Have only ONE copy of only ONE copy of

each chromosome.each chromosome.• NO HOMOLOGOUS NO HOMOLOGOUS

PAIRS presentPAIRS present• Gametes (sex cells: Gametes (sex cells:

egg and sperm)egg and sperm)• Made by Made by MEIOSISMEIOSIS• ““1n”1n”

Mitosis- divides somatic cells to get tissues and organs built; makes individual grow into an adult