Meiosis/ Karyotypes Unit 6

Part 1: Chromosomes

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

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

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

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

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

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? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Abnormal Karyotypes

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

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

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

Meiosis

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

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?

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)

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

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

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