MEIOSIS Making Sex Cells

Somatic cell = body cell Get the Lingo Down!!! Somatic cell = body cell Skin Nerve Blood

Human Chromosomes How many chromosomes? 46 How many pairs of chromosomes? 23

Homologous Chromosomes Two sister chromatids joined at the centromere From MOTHER plus Two sister chromatids joined at the centromere From FATHER = All Four Chromatids carrying genes controlling the same inherited characteristics

Loci The place on a chromosome where a specific gene is located The plural is "loci," not "locuses." EXAMPLE: gene for hair color Gene for height

Autosomes Any chromosome that is not a sex chromosome Humans - #1 through #22

Sex Chromosomes Female = XX Male = XY Chromosome #23 Is this a male or female?

Is this a male or female?

Where do we get the pair of chromosomes? One set from our father One set from our mother

Human Cells Diploid number 2n 46 somatic cells Haploid number n 23 sex cells

Sex Cells “Gametes” EX: Egg and Sperm

Single set of chromosomes Are Gametes n or 2n? N Single set of chromosomes

Are Gametes haploid or diploid? -n 23 chromosomes egg 23 sperm

Fertilization Fusing of Egg and Sperm Woo-Hoo! What’s the Fertilized egg called? Zygote

Where are the sex cells made? Testes make sperm Ovaries make eggs Only in reproductive organs

What is the process… In which sex cells are made? MEIOSIS

How many cells formed? Haploid or Diploid? 4 haploid 2 diploid

MEIOSIS INTERPHASE Yes, the chromosomes duplicate Still chromatin, loose

Meiosis I: Prophase I 90% of meiosis time

Meiosis I: Prophase I Synapsis: formation of a tetrad (4 homologous chromosomes)

Let’s Review: All DNA and Protein

With Jonathan Edwards…whatever happened to him, anyway?

Let’s See a Close-up: Crossing Over

Chiasma Sites of crossing over Appear as X-shaped regions Site where two homologous chromosomes are attached to each other

Genetic Recombination The production of gene combinations different from those carried by the original chromosomes ADVANTAGE: increases diversity

What else happens Prophase I? What dissolves? Nuclear Membrane and Nucleolus

What else happens Prophase I? What also forms? spindles

Meiosis I: Metaphase I Where are the tetrads lined up? Metaphase plate

Meiosis I: Anaphase I Where are the sister chromatids going? Apart to the poles NOTE: the double strands

Meiosis I: Telophase I Note the double strands at the poles Cytokinesis begins

Interkinesis/Cytokinesis Some cells will go into a temporary chromatin-forming interphase (like in humans) called interkinesis

Interkinesis/Cytokinesis Some will immediately go into Prophase II NOT ALL CELLS DO THIS AT THE SAME TIME…BUT ALL WILL EVENTUALLY GO INTO PROPHASE II

Interkinesis/Cytokinesis (Different than mitosis interphase, however) NO NEW DUPLICATION OF CHROMOSOMES… FURTHER DIVISION OF THE CHROMOSOMES WILL OCCUR

Meiosis II: Prophase II How many cells are there? 2 What is dissolving? Nuclear membrane What’s forming? New spindles

Meiosis II: Metaphase II How many cells? 2 Where are the chromatids lined up? Metaphase (equatorial plate)

Meiosis II: Anaphase II How many cells? 2 What are the single chromosomes doing? Moving to poles

Meiosis II:Telophase II How many cells will result at the end? 4 Will the cells be haploid or diploid? Haploid

Name the Phase (Meiosis I)

Name the Phase (Meiosis II)

Sperm Meiosis All cells same size

Sperm maturing in a seminiferous tubule

Egg Meiosis One large egg, 3 small polar bodies “oogenesis”

Follicle and egg

Results in 2 daughter cells Contrast MITOSIS 1 division (PMAT) Results in 2 daughter cells MEIOSIS 2 divisions (PMAT) I and (PMAT) II Results in 4 daughter cells

Contrast MITOSIS Diploid offspring Makes somatic cells MEIOSIS Haploid offspring Makes sex cells

Contrast MITOSIS Makes identical cells Same number of chromosomes MEIOSIS Makes similar cells Half the number of chromosomes

Independent Assortment This means that traits are transmitted to offspring independently of one another. Independent Assortment Animation

Independent Assortment In other words, RANDOM COMBINATION OF ALLELES APPEAR IN THE GAMETES

How many possible combinations are there? n = haploid number 22 = ? 8

When one man (223) combines with one woman (223)? How many combos? When one man (223) combines with one woman (223)? 246

How many combos from independent assortment: HUMANS 223 = ? About 8 million (8,388,608)

If only one crossover occurs, how many possible combinations? (70,368,744,000,000)

With fertilization and crossing-over, how many combos possible? (4 23) 2 = 4,951,760,200,000,000,000,000,000,000

Wait a second… What are alleles?

Alleles Different Versions of Genes FOR EXAMPLE: B = brown eye color b = blue eye color FOR EXAMPLE: T = Tall t = short

More Allele Examples (fruit) Hi = Hard rind inhibitor Hr = Hard rind l = light fruit color Rd = dominant = Red skin color of fruit St = stripped fruit lengthwise Rd = dominant = Red skin color of fruit

Dog Breeds: Lots of Alleles

Dog Color Alleles in order of decreasing dominance: Ay - agouti "red" (black, if any, appears in restricted areas only) Aw - "white-bellied" agouti A - solid agouti at - black & tan a – non agouti (recessive black) Ea - dominant black Em - black mask

Why are the cells formed in meiosis different from the parents? Random Fertilization (who ya have sex with) Independent Assortment Crossing Over

So an advantage of Meiosis… A tremendous amount of genetic variation is possible!

Let’s Review Three sources of genetic variability: 1. Crossing over during prophase I of meiosis 2. Independent orientation of chromosomes at metaphase I 3. Random fertilization

Karyotype An orderly display of magnified images of the individual’s chromosomes Shows the chromosomes as they appear in metaphase

What is a Normal Karyotype? We are supposed to have 46 total chromosomes in each cell (22 pairs of autosomes = 44, + 2 sex chromosomes).

Preparing a Karyotype 1. Use lymphocytes (white blood cells) 2. Chemical to stimulate division 3. Chemical to stop in metaphase (stop spindle fibers forming)

Preparing a Karyotype (cont) 4. Centrifuged to remove white blood cells 5. Chromosomes spread out in hypotonic solution. 6. Drop on a slide. 7.Sort by size and shape.

Resulting Photograph Sort by size and shape Largest to smallest

Amniocentesis Take fluid from amniotic fluid around the baby

Spectral Karyotype

Normal Karyotype WHY?

Down Syndrome Karyotype Trisomy 21

Down Syndrome Trisomy 21 Folds over eyes Sluggish muscles Mental Problems

Down Syndrome The most common chromosome number abnormality Round face flattened nose bridge small, irregular teeth

Down Syndrome Short Stature heart defects susceptibility to respiratory infection , leukemia and Alzheimer’s

Does the mother’s age matter? As the age of the mother increases above 30, the frequency of Trisomy 21 also increases

Abnormal Sex Chromosomes 47 XXY syndrome male testes small (sterile) breast enlargement feminine body contours also XXYY, XXXY, XXXXY Klinefelter’s

TURNER SYNDROME XO (only one X) short often web of skin between neck and shoulders sterile poor breast development

Turner Karyotype

Why are the cells formed in meiosis different from the parents? Random Fertilization (who ya have sex with) Independent Assortment Crossing Over

How many possible combinations are there? n = haploid number 22 = ? 8

DELETION Fragment of the chromosome is lost

Duplication Fragment of one chromosome attaches to a homologous chromosome

Translocation Fragment reattaches in reverse direction (less likely to produce harm)

INVERSION The chromosome breaks in two places, a piece of the chromosome is removed and the chromosome pieces remaining rejoin. Less likely to remove harm

The left one is normal and the right one is inverted near the centromere. Inversions, by definition, do not involve loss or gain of chromosomal material. INVERSION 46,XY,inv(16)

45,XX,rob(13,14) A Robertsonian translocation (an end to end fusion of #13 and #14 There is no net gain or loss of genetic material in this person so they would have a normal phenotype. 45,XX,rob(13,14) A Robertsonian translocation

Locus

Broccoli + Cauliflower = Broccoflower

Male Lion X Female Tiger Liger