Sexual Reproduction and Meiosis Chapter 7b Copyright © McGraw-Hill Companies Permission required for reproduction or display

Reduction Division In sexual reproduction, gametes fuse (fertilization) to produce a zygote. Gamete formation involves a mechanism (meiosis) that reduces the number of chromosomes to half that found in other body cells. Adult somatic (body) cells are diploid. Gamete (reproductive) cells are hapolid.

Unique Features of Meiosis (What makes it different from Mitosis) Synapsis Homologues pair along their length. Homologous Recombination Genetic exchange (crossing over) occurs between homologous chromosomes. Reduction Division Chromosomes do not replicate between the two nuclear divisions.

The most important difference between meiosis and mitosis is that meiosis produces _____ cells. Four diploid Four haploid Two haploid Somatic

Prophase I Chromosomes condense\ Homologous chromosomes pair up Crossing over may occur while chromosomes are very close together Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Crossing Over-during Prophase I Chiasmata are X-shaped structures Presence of chiasmata indicates crossing over has occured

Metaphase I Homologues line up on metaphase plate (equator). Orientation of each pair is random (mom’s chromosomes vs. dad’s choromosomes may be to the right or to the left) Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Anaphase I Homologues separate Each pole receives a member of each homologous pair. Due to random orientation, meiosis results in independent assortment. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Telophase I Chromosomes segregated into two clusters. Nuclear membrane re-forms around each daughter cell. Cells are not identical Cytokinesis occurs to form 2 haploid cells Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

No replication of DNA occurs between Meiosis I and Meiosis II Prophase II - Nuclear envelope breaks down and second meiotic division begins. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Spindle fibers bind to both sides of centromere Meiosis II Metaphase II – Spindle fibers bind to both sides of centromere Chromosomes line up (single file) along equator Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Meiosis II Anaphase II - Spindle fibers contract and sister chromatids move to opposite poles. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Telophase II - Nuclear envelope re-forms. Meiosis II Telophase II - Nuclear envelope re-forms. Final Result – Cytokinesis makes 4 haploid cells. Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Which meiosis phase listed below is the most different from mitosis? Prophase II Metaphase I Telophase II Cytokinesis

Types of Reproduction Asexual Reproduction - Individual inherits all its chromosomes from a single parent. Sexual Reproduction - Produces genetic variability. Segregation of chromosomes tends to disrupt advantageous combinations. Only some progeny maintain advantages. Parthenogenesis Development of adult from unfertilized egg.

Mendelian Genetics Gregor Mendel (1822-1884) Austrian monk Observed plants in the monastery garden Father of Genetics for determining inheritance patterns in peas

Punnett Squares Tool used to predict the next generation of offspring P1 cross Cross between two parents pure for a trait Produces F1 generation F1 cross Cross between the first generation offspring Produces F2 generation

What is the genotype that belongs in square 1? TT Tt tt None of the above 1

Punnett Squares Genotype is the letter combination of the alleles GG, Gg, or gg Phenotype is the manifestation (what trait is produced) Green or yellow

What is the phenotype of the yellow peas? Green Yellow GG Gg

What is the genotype of the yellow peas? Green Yellow gg Gg