1. Meiosis/ Karyotypes
Unit 6

2. Part 1: Chromosomes

3. Differences among Species
Humans have 46 chromosomes
Differences among Species
Each species has a characteristic number of chromosomes
Oats, Raccoon Dogs, Rats, Wheat and Wolverines all have 42 chromosomes
Potatoes, plums, and chimpanzees all have 48 chromosomes

4. Chromosome- Gene- Composed of DNA and protein.
Consist of 2 identical CHROMATIDS attached by a CENTROMERE when the cell is ready to divide (after S of interphase)
(Before division, chromatids separate to ensure identical DNA in both)
Gene-
Units of information
Segment of DNA that codes for a protein or RNA molecule

5. Somatic Cells What are somatic cells? Have 46 chromosomes in humans.
Differ in size, shape, and genes
23 pairs
2 HOMOLOGOUS chromosomes that are similar in size, shape, and genes
One comes from each parent!
Diploid (2n)
Contains 2 sets of chromosomes
In humans, 2n=46

6. Gametes What are gamets? Contain 1 set of chromosomes Haploid (n)
23 in humans
Haploid (n)
In humans n=23
Fusion of 2 gametes= FERTILIZATION
Fertilized egg cell is a zygote
23 chromosomes+23 chromosomes=46Chromosomes
n+n=2n

7. Chromosomes Autosomes: Sex Chromosomes:
22 of the 23 pairs of chromosomes in somatic cells (44 of 46 chromosomes)
Sex Chromosomes:
1 of the 23 pairs (2 of the 46 chromosomes)
XX or XY in humans
XO system for birds and butterflies

8. Karyotype - photograph of chromosomes grouped in order from largest to smallest in pairs; used to analyze chromosomes
This is a human karyotype.
How many chromosomes are shown?
Was this made from the nucleus of a somatic cell or a gamete?
How many autosomes are shown?
How many sex chromosomes?
Is this from a male or a female?
How do you know?

9. Abnormal Karyotypes

10. Nondisjunction
Sometimes during meiosis, the chromosomes fail to separate correctly (called nondisjunction)
Monosomy- when gamete has only 1 copy of the affected chromosome
Turner’s syndrome:
Only one sex chromosome
No Y= develops into female
Ex. XO
Trisomy- when the other gamete has 3 copies of one chromosome
Klinefelter’s syndrome:
One to several extra sex chromosomes
Ex. XXY or XXXY

11. Nondisjunction Down’s Syndrome: Patau Syndrome: Autosomal Trisomy 21
Most common birth defect
Patau Syndrome:
Autosomal
Trisomy 13
Rarely live past infancy
Neurological problems, polydactyl and facial defects

12. Nondisjunction Edwards Syndrome: Autosomal Trisomy 18
30% of babies die by 1 month
Small head, Clenched hands with 2nd and 5th fingers on top of the others, Learning disabilities, congenital heart defects and malformations of digestive tract, urinary tract and genitals

13. Meiosis

14. What is Meiosis?
A form of cell division that produces sex cells (gametes) used in fertilization

15. How is Meiosis Different?
There are 2 divisions in meiosis (Meiosis I and II)
The result is 4 cells instead of 2
The ending number of chromosomes is 23 in humans (egg has 23 and sperm has 23)
Is this haploid or diploid?

16. Mitosis Vs. Meiosis Mitosis 1 division= 2 cells
Daughter cells identical
Diploid cells (2n)= 46
Body/somatic cells
Meiosis
2 divisions= 4 cells
Daughter cells different
Haploid cells (n)=23
Gametes (sex cells=egg/sperm)

18. Why are the daughter cells in meiosis different??
Genetic Variation!
Crossing Over-
During prophase I pieces of homologous chromosomes are exchanged.

19. Why are the daughter cells in meiosis different??
Genetic Variation!
Independent Assortment-
Homologous chromosomes are randomly sorted/distributed during metaphase I and II.
(Which chromosomes go to which cell is random)
*This picture would be of an organism that only had 2 chromosomes

20. Why are the daughter cells in meiosis different??
Genetic Variation!
Random fertilization- the fertilization of an egg and sperm is random!