Chromosomes
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Chromosomes Objectives: Explain how karyotypes can be used to identify chromosomal abnormalities Identify the chromosomes responsible for a person’s sex Chromosomes Supercoiled complex of DNA and proteins DNA codes for LOTS of things The codes must be neatly organized

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Chromosomes

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Chromosomes

Objectives:

  • Explain how karyotypes can be used to identify chromosomal abnormalities

  • Identify the chromosomes responsible for a person’s sex


Chromosomes

  • Supercoiled complex of DNA and proteins

  • DNA codes for LOTS of things

  • The codes must be neatly organized

  • The codes are organized into genes

  • Chromosomes are stacks of genes


Supercoiling


Chromosomes

  • Chromosomes found in metaphase will have 2 chromatids and will be attached by a centromere

  • The chromatids are identical


Chromatin

  • DNA usually exists in chromatin

  • Chromatin is a uncoiled DNA and protein complex

  • Chromatin only supercoils when cells are entering mitosis or meiosis


Harvesting Chromosomes

  • Chromosomes develop from chromatin during prophase

  • They are clearly seen in metaphase since there is no nuclear membrane


Harvesting Chromosomes

  • Cells are frozen in metaphase

  • Chromosomes are then treated and stained

  • They are viewed under a microscope

  • A photograph is taken

  • The photograph is enlarged and the chromosomes are cut out


Karyotype Equipment


Karyotypes

  • Homologous chromosomes are paired

  • The pairs are arranged by size and in order with their centromeres aligned


Ploidy

  • Not all organisms have 23 pairs of chromosomes

  • 2N = diploid

  • N = haploid

  • 2N = 46 for humans

  • N = 23 for humans

  • Find the ploidy of the organisms listed


Sex Chromosomes

  • The first 22 pairs of chromosomes are called autosomes

  • The 23rd pair of chromosomes are called sex chromosomes

  • They code for whether the individual will be male or female

  • If the 23rd pair is homologous the individual is a female

  • If the 23rd pair is non-homologous the individual is a male


Sex Chromosomes

  • The chromosomes are referred to as X and Y

  • XX = female

  • XY = male

  • The Y has significantly less genes on it than the X


Sex Chromosomes

Male

Female


2n=46. Human

We use karyotypes to find genetic disorders.

And to determine the sex of the individual.


Karyotypes Homework

  • Find the pairs

  • Arrange them in pairs, in order of size, with the same line going through each pair’s centromeres

  • Paste the pairs in your comp book

  • Is the person a male or a female?

  • Is there a genetic disorder?


Karyotype Homework

  • Google karyotype

  • Print one of a non-human organism

  • Paste it to your compbook

  • Remember to identify what organism you chose


Socks

Male

FYI: Socks aren’t really organisms.


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