Understanding Heredity and Meiosis in Offspring

2. Chapter 13 A. Heredity • Offspring acquire genes from parents by inheriting chromosomes. • Most genes program cells to synthesize specific proteins. • Inheritance is possible because DNA is precisely replicated producing copies of genes that can be passed on. • Chromosomes contain hundreds of genes, each is a specific region of the DNA molecule called the locus.

4. Chapter 13 B. Asexual VS Sexual • In Asexual reproduction a single individual is the parent. This single parent passes all its genes to its offspring. Results in a clone or genetically identical organism. • In Sexual reproduction, two parents give rise to offspring. Each parent passes half it genes to the offspring. It results in greater genetic variation.

5. Chapter 13 C. The Role of Meiosis • Vocabulary ** • Somatic cell- any cell other than sperm and eggs. • Karyotype- a display of an individuals somatic cells. They are used to match homologous pairs. They are usually made w/lymphocytes. • Homologues are a pair of chromosomes that have the same size and position. • Autosome- chromosomes that are not sex chromosomes. • Diploid-2n- 2 sets of chromosomes. • Haploid-n- 1 pair of chromosomes. • Gamete- haploid reproductive cells. • Zygote- a diploid cell that results from 2 haploid gametes

6. Chapter 13 D. Sexual Life Cycle • Animals- Meiosis occurs during gamete production. The resulting gametes undergo no further cell division before fertilization. • Fertilization produces a diploid zygote that divides by mitosis to produce a diploid multicellular animal

7. Chapter 13 ** E. Sexual Life Cycle ** • Plants and some algae alternate between multicellular haploid and diploid generations. • This type of life cycle is called a alternation of generations. The multicellular diploid stage is called a sporophyte, or spore producing plant. – • Haploid spores divide mitotically to generate a multicellular haploid stage called a gametophyte, or gamete producing plant. Haploid gametophytes produce gamete by mitosis. • Fertilization produces a diploid zygote which becomes the next sporophyte generation

8. Chapter 13 F. Meiosis ** • Meiosis differs from mitosis in that this single replication is followed by 2 consecutive cell divisions meiosis I and meiosis II • These cell divisions produce 4 daughter cells instead of 2 as in mitosis. • The resulting daughter cells have half the number of chromosomes.

9. Chapter 13 G. The stages of meiosis • Meiosis I • Interphase I – chromosome replicate. Each duplicated chromosome consists of two identical chromatid. • Meiosis I – This cell division segregates the two chromosomes of each homologous pair and reduces the chromosome number by one-half.

10. Chapter 13 ** H. Meiosis I • Prophase I – The chromosome condense, synapsis occurs, homologous chromosomes come together as pairs. Each chromosome has two chromatids • Tetrads form- paired homologues. In each tetrad, sister chromatids of each chromosome are attached at their centromeres. Non-sister chromatids are linked by X-shaped chiasmata, sites where homologous strands exchange or crossing over occurs.

11. Chapter 13 I. Meiosis I • Prophase I is also characterized by the nuclear envelope and nucleoli dispersing. This phase occupies 90% meiosis. • Metaphase I- Tetrad align on the metaphase plate. Each homologue is attached to kinetochores microtubules emerging form the poles it faces, so the homologs will separate in anaphase, and move to opposite poles.

12. Chapter 13 J. Meiosis I • Anaphase I – Homologues separate and are moved toward the poles by the spindles. Sister chromatid remain attached at their centromeres and move toward the same poles, while the homologues move toward the opposite poles • Telophase I & Cytokinesis is characterized by the spindle apparatus separating homologous chromosome pairs until the chromosomes reach the poles. • Some species have interkinesis, the nuclear membrane and nucleoli reappear. • For all species, no DNA replication occurs before meiosis II

13. Chapter 13 K. Meiosis II ** #3 • The same process continues, Pro. II  Meta. II  Ana. II  Telo. II • In this second meiotic division sister chromatid separate in the end, four haploid daughter cells are made. • Meiosis and fertilization are the primary sources of genetic variation in sexually reproducing organisms, w/ independent assortment, crossing over pro. I , and random fusion

14. Chapter 13 L. Independent Assortment • Independent assortment is the random distribution of maternal and paternal homologues to the gametes.(random assortment of genes on different chromosomes) • Crossing over-the exchange of genetic material between homologues; occurs during prophase of meiosis I. (chiasmata) • Random fertilization is another source of genetic variation. • Evolutionary adaptation depends on a populations genetic variation.

15. Chapter 14 A. Useful Vocabulary ** • Homozygous- having 2 identical alleles for a trait. PP, pp • Heterozygous- having 2 diff. alleles for a trait Pp • Phenotype- an expressed trait. Purple,wht,wrinkled • Genotype- an organisms genetic makeup PP pp Pp • Testcross- Breeding 2 organisms, PP X Pp

16. ExAMPLES TO KNOW ** • Homozygous recessive • Heterozygous & Homozygous dominant