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DNA, Chromosomes and Genes

Jamie Z 2024-10-14

Learning Goals

    1. Define heritable characteristics
    1. Appreciate that all organisms have heritable characteristics
    1. Identify examples of heritable characteristics
    1. Define: chromosomes, genes, DNA
    1. Describe the relationship between DNA, genes and chromosomes
    1. Define the terms: karyotype, homologous chromosome, sex chromosome
    1. Identify the number of chromosomes in somatic (body) cells and in gametes
    1. Define the terms: diploid, haploid
    1. Describe the difference between X and Y chromosomes
    1. Explain the difference in the karyotype for a normal male and female

What is Genetics?

Genetics is the study of how hereditary traits in an individual are transmitted from one generation to the next

Heredity

Passing on traits from parents to offspring

  • A heritable trait is a characteristic which is capable of being inherited
  • E.g. Height, eye colour, hair colour

Variation

  • Genetic variation refers to the differences in genetic makeup of individuals
  • Some of these variations are genetic in origin
  • Some variations are due to environmental differences (which are not passed on)

Chromosomes

Chromosomes are long strands of genetic information located in the nuclei of the cell

Homologous pairs of chromosomes

  • In most cells, chromosomes are matched in pairs based on their size and shape
  • Matching pairs of chromosomes are called homologous chromosomes
  • A chromosomes come in homologous pairs, genes genes in pairs
  • Each pair of homologous chromosomes contain one chromosome that has been inherited from each parent

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Human Chromosomes

  • In the human body there are a total of 46 chromosomes
  • There are 23 pairs of chromosomes
  • You inherit half from your mother and half from your father

Sex chromosomes

  • A sex chromosome is a type of chromosome that participates in sex determination
  • There are two types: X chromosomes and Y chromosome
  • The Y is one third the size of the X and contains about 55 genes while the X chromosome has about 900 genes
  • Females have two X chromosomes from each parent
  • Males have one X chromosome and one Y chromosome

Haploid and Diploid Cells

  • Diploid describes a cell or organism that has paired chromosomes, one from each parent.
  • Human sex cells contain a single set of chromosomes and are known as haploid

Chromosomes

  • Imagine each chromosome is like a string of plastic beads (a single line not joined to form a loop)

DNA

  • Stands for deoxyribonucleic acid
  • DNA is the substance that chromosomes and genes are made of
  • It is like a bead on the chain

Genes

  • Each chromosomes consists of many thousands of genes
  • A gene is a segment of DNA that codes for one particular protein

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