Intro Genetics and Meiosis

Chapter 13

Vocabularyheredityvariationgenegametesomatic cellasexual vs sexual

reproductionautosomessex chromosomesalleledominant vs recessivediploid vs haploid

parental generationfilial generationheterozygoushomozygousphenotypegenotypesex-linked geneLocusTraittrue-breedinghybrid

Where does genetic diversity come from?

original source is mutations (mistakes in DNA) that result in different alleles

sexual reproduction causes reshuffling of the alleles to produce a population with a unique combination of traits

Chromosome Anatomy RevisitedHumans = 46

chromosomes (23 pairs)

for analysis, chromosomes organized into karyotypes

homologous chromosomes (pairs), each contain genes controlling the same inherited characteristics

one chromosome is inherited from each parent (dominant allele is expressed--usually)

Meiosiscell division in sperm and egg cells

(produces haploid cells)In humans, 23 chromosomes

two cells unite during fertilization to produce diploid cell (zygote)In humans, 46 chromosomes

goal to ensure genetic diversity in sexually reproducing organisms

(figure 13.8)

Meiosis I (separates homologous chromosomes)crossing over occurs

during prophase Iotherwise identical

steps to mitosis (non-identical haploid cells produced)

Meiosis II (separates sister chromatids)identical steps to

mitosis (produces non-identical haploid cells)

GametogenesisProduction of gametes (sperm/egg cells)

Within the testes/ovaries precursor cells (spermatocytes and oocytes) exist in the diploid form

These precursor cells then go through meiosis to form haploid sperm/egg cells which are used in sexual reproduction to produce offspring Spermatogenesis Oogenesis

Meiosis…again.Reduction Division (creates haploid cells)

Meiosis I Two HAPLOID cells produced Chromosomes have crossed over

Meiosis II Four HAPLOID cells produced Genetically unique cells

Ensures genetic diversity of a species through…Independent assortment of homologous

chromosomesCrossing over of homologous chromosomes

Independent Assortment

During Meiosis I, maternal and paternal chromosomes align randomly on metaphase plate (daughter cell has 50/50 chance of getting either)

each pair of chromosomes is sorted independently from one another (daughter cells will have various combinations of chromosomes from mom/dad)

In humans there are over 8 million different combinations with 23 chromosomes from two parents (223)

Crossing Overoccurs during prophase I

two non-sister chromatids (tetrad) trade alleles thus combining genetic information from two parents

Chiasma: site of crossing over

results in genetic recombination (offspring with different combination of traits than parents)

Coupled with independent assortment, this results in over 23 trillion different combinations from both parents

You are 1 in 23 trillion!

recombinant chromosomes: individual chromosomes that carry genes derived from two different parents

1-3 cross-over events per pair of chromosomes at most

Mr. Knuffke Meiosis Prezi LinkAwesome meiosis square dancing video!

https://prezi.com/el-sh-qgrgsj/ap-bio-information-7-meiosis/

Mitosis vs. Meiosis(figure 13.9)