2 Homologous Chromosomes In the body cells, or somatic cells, of animals and most plants, chromosomes occur in pairs.One from mom, one from dadPairs are called homologous chromosomesNormal body cells are diploid cells because the nave the full number of chromosomes, or n.In humans, 2n = 46.
3 Organisms that reproduce sexually need special sex cells that contain half the normal number of chromosomes.Sex cells are called gametes.These gametes are haploid cells and have the n amount of chromosomes.In humans, n = 23.
4 Chromosome numbersDo all organisms have the same number of chromosomes?
5 Homologous Chromosomes sex chromosomesautosomesHow many autosomes are found in the human the body cell?44 (22 pairs)Match up the homologous chromosomes
6 MeiosisMeiosis is a two-part cell division process that produces gametes or sex cells.four daughter cellsall daughter cells are haploidchromosomes are shuffled in the process, so that each daughter cell has a unique combination of genes (crossing over)
9 Crossing OverTo make things more interesting, crossing over can occur.During prophase, the homologous chromosomes form tetrads.
10 Crossing OverCrossing over takes place when two chromosomes break and then reconnect but to different end piece.Crossing over increases the number of variations that can exist in offspring.
11 Crossing OverWhich of the following did crossing over ONLY take place?BAC
12 Fertilization Male sex cells are called sperm. Female sex cells are called eggs.When two sex cells unite, fertilization occurs.A fertilized egg is called a zygote.This is the first cell of the new offspring!
13 NondisjunctionAlthough the events of meiosis usually proceed accurately, sometimes an accident occurs and the chromosomes fail to separate correctly. This is known as nondisjunction.
15 NondisjunctionThe zygote that has been created will have an extra or missing chromosome. This would result in an inherited genetic disorder.In most cases, the presence of an additional chromosome or missing chromosome results in the death of the zygote.
16 NondisjunctionIn humans, n = 23. So the normal body cell is 2n = 46 chromosomes.What would happen if a gamete containing an extra chromosome(n+1) were to be paired with a gamete containing the correct number of chromosomes (n)?The zygote that has been created will have and diploid number of chromosomes n+1 = 47 chromosomes.n+1n
17 KaryotypesWhen you are born, doctors take a sample of your blood and create a karyotype. This will enable the doctor to see if you have any additional or missing chromosomes.A karyotype is a standardized arrangement of all the chromosomes of a cell.
18 KaryotypesHomologous chromosomes are paired up, then they are put in order from the LARGEST chromosome pair to the smallest.
19 Karyotypes2 x chromosomes=GIRLautosomessex chromosomes
20 Karyotypes Everything okay here?? What gender?? 2 different sized sex chromosomes = XY = male
21 Down’s syndrome Everything okay here?? trisomy 21 trisomy 21 decreased muscle tone at birthasymmetrical or odd-shaped skullround head with flat area at the back of the headslanting eyessmall mouth with protruding tonguesingle crease on the palmslowed growth and developmentdelayed mental and social skillstrisomy 21trisomy 21
22 Turner’s syndrome Everything okay here?? monosomy X monosomy X short stature (affects almost all girls with Turner, to different degrees)failure of ovaries to develop (90-95% of girls)webbed neck (25%) or short neck (40%)abnormal fingernails and toenails (70%)hearing disorders (50-90%)frequent ear infections in childhood (75%)monosomy Xmonosomy Xmonosomy X
25 Kleinfelter’s syndrome No symptoms - some men are unaware they have an extra chromosomeEnlarged male breasts - only severe in about 10% of casesSparse facial hairSparse body hairInability to produce spermTallness - more likely to be taller than non-XXY males.ThinnessNormal intelligenceLanguage impairmentDelayed languageXXYXXY