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
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
Meiosis I: Anaphase I
Where are the sister chromatids going?
Apart to the poles
NOTE: the double strands
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:Telophase II
How many cells will result at the end?
4
Will the cells be haploid or diploid?Haploid
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
If only one crossover occurs, how many possible combinations?
• 423 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
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 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 & tana – 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
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.
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
Why are the cells formed in meiosis different from the
parents?
• Random Fertilization (who ya have sex with)
• Independent Assortment
• Crossing Over
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
INVERSION 46,XY,inv(16)
• 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.
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.
Top Related