Question

chromosomes & meiosis - guided notes
learning target:
i can describe chromosome structure and use a karyotype to identify autosomes, sex
chromosomes, and chromosomal abnormalities.
early discoveries
what did anton van leeuwenhoek call the tiny, animal - like molecules he saw under the
microscope?
chromosomes
improved microscopes revealed that each cell has structures called chromosomes.

• the number of chromosomes depends on the
• chromosomes come in matching sets called pairs.
• chromosomes are numbered by
• one set of chromosomes are the chromosomes.

when looking at egg and sperm cells, scientists discovered they only have the number of
chromosomes compared to other body cells. body cells in humans have 46.
how many chromosomes are in sperm cells?
how many sex chromosomes are in a sperm cell?
homologous chromosomes are the same size and have the same pattern.
body cells () are (2n). in humans this is total chromosomes.
sex cells (- sperm & eggs) have half of the normal # of chromosomes - they are
called (n). egg and sperm fuse during fertilization to restore the #
why do sex cells need only half the number of chromosomes?
chromosome structure label the parts on your chromosome diagram:
centromere • chromatid • sister chromatids • gene

Explanation:

• Early Discoveries: Anton van Leeuwenhoek called the tiny, animal - like molecules he saw under the microscope "animalcules".
• Chromosomes:
• The number of chromosomes depends on the species.
• Chromosomes come in matching sets called homologous pairs.
• Chromosomes are numbered by length.
• One set of chromosomes are the sex chromosomes.
• Egg and sperm cells have half the number of chromosomes compared to other body cells. Since human body cells have 46 chromosomes, sperm cells have \(46\div2 = 23\) chromosomes. And there is 1 sex chromosome in a sperm cell (either X or Y).
• Homologous chromosomes are the same size and have the same banding pattern.
• Body Cells (somatic cells) are diploid (\(2n\)). In humans, this is 46 total chromosomes. Sex cells (gametes - sperm & eggs) have half of the normal # of chromosomes - they are called haploid (\(n\)). Egg and sperm fuse during fertilization to restore the diploid #.
• Sex cells need only half the number of chromosomes so that when sperm and egg fuse during fertilization, the resulting zygote has the correct (diploid) number of chromosomes for the species. For example, in humans, if sex cells had the same number of chromosomes as somatic cells (46), the zygote would have \(46 + 46=92\) chromosomes, which is incorrect.

Answer:

• Anton van Leeuwenhoek: animalcules
• Chromosome number: species
• Chromosome pairs: homologous
• Chromosome numbering: length
• One set: sex
• Sperm cell chromosomes: 23
• Sperm cell sex chromosomes: 1
• Homologous chromosomes: banding
• Body cells: somatic cells, diploid, 46
• Sex cells: gametes, haploid
• Fertilization: diploid
• Sex cell chromosome reason: So that when sperm and egg fuse during fertilization, the resulting zygote has the correct (diploid) number of chromosomes for the species.