Meiosis and Sexual Life Cycles Chapter 13

Reproduction Why do offspring closely resemble their parents and not unrelated individuals? Heredity =

Reproduction Why do offspring closely resemble their parents and not unrelated individuals? Heredity = passing of genes from parents to offspring variation =

Reproduction Why do offspring closely resemble their parents and not unrelated individuals? Heredity = passing of genes from parents to offspring variation = inherited differences within a species DNA =

Reproduction Why do offspring closely resemble their parents and not unrelated individuals? Heredity = passing of genes from parents to offspring variation = inherited differences within a species DNA = Nucleic acid polymer with bases A,C,T, and G genes =

Reproduction Why do offspring closely resemble their parents and not unrelated individuals? Heredity = passing of genes from parents to offspring variation = inherited differences within a species DNA = Nucleic acid polymer with bases A,C,T, and G genes =

Reproduction Why do offspring closely resemble their parents and not unrelated individuals? Heredity = passing of genes from parents to offspring variation = inherited differences within a species DNA = Nucleic acid polymer with bases A,C,T, and G genes = units of heredity; made of DNA found on the chromosomes

Asexual Reproduction What occurs in asexual reproduction? Single individual is the parent which copies all of its genes into an identically cloned offspring. Limited variation with asexual reproduction. What nuclear division is involved in asexual reproduction?

Sexual Reproduction In order for 2 parents to combine their genes into one offspring, what must their genetic contribution be? Each parent must contribute 1/2 of their genes to the offspring. How does the process ensure that the offspring receives the correct genes from each parent?

Vocabulary of genetics and reproduction Somatic cell =

Vocabulary of genetics and reproduction Somatic cell = any cell other than sperm or egg. Human somatic cells have 46 chromosomes karyotype =

Vocabulary of genetics and reproduction Somatic cell = any cell other than sperm or egg. Human somatic cells have 46 chromosomes karyotype = display of individuals somatic cell metaphase chromosomes. Homologous chromosomes =

Vocabulary of genetics and reproduction Somatic cell = any cell other than sperm or egg. Human somatic cells have 46 chromosomes karyotype = display of individuals somatic cell metaphase chromosomes. Homologous chromosomes = chromosomes that have same centromere position, same genetic loci, and same length. How, then, are homologous chromosomes different from one another?

Homologous chromosomes have different alleles.

Homologous chromosomes have different alleles. Allele = expression of a gene autosome =

Homologous chromosomes have different alleles. Allele = expression of a gene autosome = non-sex chromosome sex chromosome =

Homologous chromosomes have different alleles. Allele = expression of a gene autosome = non-sex chromosome sex chromosome = dissimilar chromosomes that determine an individual’s sex. How many autosomes and how many sex chromosomes are there in a normal human? How many homologous pairs of chromosomes?

diploid =

diploid = condition in which cell contains 2 sets of chromosomes; abbreviated 2n haploid =

diploid = condition in which cell contains 2 sets of chromosomes; abbreviated 2n haploid = condition in which cells contain 1 set ( no homologous pairs) of chromosomes; abbreviated n gamete =

diploid = condition in which cell contains 2 sets of chromosomes; abbreviated 2n haploid = condition in which cells contain 1 set 9 no homologous pairs) of chromosomes; abbreviated n gamete = haploid reproductive cells, human gametes have 23 chromosomes fertilization =

diploid = condition in which cell contains 2 sets of chromosomes; abbreviated 2n haploid = condition in which cells contain 1 set 9 no homologous pairs) of chromosomes; abbreviated n gamete = haploid reproductive cells, human gametes have 23 chromosomes fertilization = union of 2 gametes zygote =

diploid = condition in which cell contains 2 sets of chromosomes; abbreviated 2n haploid = condition in which cells contain 1 set 9 no homologous pairs) of chromosomes; abbreviated n gamete = haploid reproductive cells, human gametes have 23 chromosomes fertilization = union of 2 gametes zygote = diploid cell that results from fusion of gametes What sort of nuclear division must occur to produce haploid gametes?

Meiosis Must have a stage that results in the reduction of chromosome number. In meiosis the diploid parent cell produces haploid gametes

Interphase I What happens in interphase I? Chromosomes replicate centriole pairs in animal cells also replicate In what way is interphase I from meiosis I different from interphase of mitosis? There is no difference.

Prophase I Synapsis occurs. Homologous chromosomes come together as pairs chromosomes appear as tetrads with 4 attached sister chromatids chiasmata form, they are sites where homologous non-sister chromatids cross over. 90% of meiosis is spent in prophase I

Metaphase I Tetrads align at metaphase plate each homologue is attached to kinetochore microtubules emerging from opposite poles, so that the 2 homologues are destined to separate during anaphase I

Anaphase I Homologous chromosomes are moved to opposite poles by spindle apparatus sister chromatids remain attached at the centromeres How does this differ from anaphase of mitosis?

Telophase I each pole has a haploid set of chromosomes cytokinesis occurs and daughter cells are formed. What is the chromosome number in each daughter cell?

What has been accomplished by the end of meiosis I? Homologous pairs of chromosomes have separated. Why isn’t meiosis over, if haploid daughter cells have already been formed? We still need to separate sister chromatids!

Genetic Variation What are the 3 ways that meiosis and sexual reproduction generate variety? Independent assortment Orientation of homologous pairs of chromosomes with regard to each-other is random (metaphase I) there is a 50/50 chance that a particular daughter cell will receive a paternal or maternal chromosome

There are 2n possible combinations of maternal and paternal chromosomes. In humans there are 223 possible different combinations or 8 million. Random fertilization has the random combining of egg and sperm. Each egg and sperm has one in 8 million different possibilities. Thus the zygote can have one in 64 trillion possible diploid combinations. This number hasn’t even accounted for crossing over, which has a random contribution to genetic variation!

Genetic Variation in all organisms In asexually reproducing organisms, mutations are the primary source of genetic variation In sexually reproducing organisms meiosis accounts for most of the variation.

Oogenesis vs. Spermatogenesis On board…