Meiosis, Karyotypes, & Nondisjunction. Ch 11 & 14

Transcription

1 Meiosis, Karyotypes, & Nondisjunction Ch 11 & 14

2 WORDS (AND CONCEPTS) TO KNOW Human somatic cells have chromosomes (replicated) homologous chromosomes = two chromosomes w/ same genes (tetrad) sister chromatids sex chromosomes, autosomes haploid (n), diploid (2n) karyotype

3 Meiosis overview The problem (Why Meiosis?) The solution 2 divisions, 4 daughter cells haploids how many interphases? Meiosis in animals: makes gametes (sperm & eggs)

4 Meiosis overview Prophase I tetrads crossing over T. H. Morgan s illustration of crossing over a tetrad of the grasshopper Chorthippus parallelus showing 5 chiasmata

5 Meiosis overview Metaphase I what lines up at metaphase plate? random orientation leads to ind. assort. Anaphase I what separates? Telo I daughter cells are haploid (2 x n) Pro II Meta II Ana II what separates? Telo II

6 Key 2n = 6 Maternal set of chromosomes (n = 3) Paternal set of chromosomes (n = 3) Two sister chromatids of one replicated chromosomes Centromere Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (tetrad)

7 MEIOSIS I: Separates homologous chromosomes PROPHASE I METAPHASE I ANAPHASE I Sister chromatids Chiasmata Centromere (with kinetochore) Spindle Metaphase plate Sister chromatids remain attached Tetrad Microtubule attached to kinetochore Homologous chromosomes separate Homologous chromosomes (red and blue) pair and exchange segments; 2n = 6 in this example Tetrads line up Pairs of homologous chromosomes split up Meiosis 1 ends with haploid cells

8 MEIOSIS II: Separates sister chromatids TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS Cleavage furrow Sister chromatids separate Haploid daughter cells forming Two haploid cells form; chromosomes are still double During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes

9 WHY SEX? Natural Selection: Repro of the fittest genetic/phenotypic variation by: Genetic reshuffling, recombination 1.independent assortment (Meta1) 2.crossing over (Pro1) random fertilization of gametes 3.Mutations

10 MITO VS MEIO Property Mitosis Meiosis DNA replication During interphase During interphase Divisions One Two Synapsis and crossing over Daughter cells, genetic composition Role in organism Do not occur Two diploid, identical to parent cell Produces cells for growth and tissue repair Form tetrads in prophase I Four haploid, different from parent cell and each other Produces gametes/spores

11 KARYOTYPE

12 Karyotype stop cells during cell division and take photo arrange by size, banding pattern

13 Karyotype In karyotyping, chromosomes are arranged in pairs according to their structure. Phenotype?

14 Karyotype In karyotyping, chromosomes are arranged in pairs according to their structure.

15 Karyotype Application: used to screen for defective chromosomes in the fetus.

16 WHEN MEIOSIS GOES WRONG Nondisjunction

17 Phenotype? Karyotype of a female with Down Syndrome aka Trisomy 21

18

19 Edwards Syndrome: Trisomy 18 Infant with Edwards Syndrome

20 Turner Syndrome Female (45 total chromosomes, 1 sex chromosome (X)) Only monosomy that is Not lethal AbnormaliCes: underdeveloped breasts, rudimentary ovaries InferCle: do Not ovulate or menstruate Treatment: Hormone supplements can help these women lead normal lives

21 Klinefelter Syndrome Karyotype

22 Klinefelter Syndrome Male,( 47 total chromosomes, 3 sex chromosomes XXY) May have some learning difficulces In severe cases: rudimentary testes & prostate gland, sparse facial and pubic hair, long arms and legs, breast development may occur InferElity

23 Also: XYY YO

24 Done

25 Pedigree Analysis A pedigree is a family tree that describes the interrelationships of parents and children across generations Inheritance patterns of particular traits can be traced and described using pedigrees Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

26 LE 14-14a Ww ww ww Ww First generation (grandparents) Ww ww ww Ww Ww ww Second generation (parents plus aunts and uncles) WW or Ww ww Third generation (two sisters) Widow s peak No widow s peak Dominant trait (widow s peak)

27 LE 14-14b First generation (grandparents) Ff Ff ff Ff Second generation (parents plus aunts and uncles) FF or Ff ff ff Ff Ff ff Third generation (two sisters) ff FF or Ff Attached earlobe Free earlobe Recessive trait (attached earlobe)

28 Pedigrees can also be used to make predictions about future offspring We can use the multiplication and addition rules to predict the probability of specific phenotypes Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings