chromosomes and genes
TRANSCRIPT
Junior Science
Chromosomes and Genes
Lesson Objectives
• Understand the terms – Chromosome, DNA, Genes and Allele.
• Explain the difference between Genotype and Phenotype.
• Give examples of dominant and recessive traits.
• Complete a simple Punnett square genetic cross.
• Chromosomes are thread-like structures located inside the nucleus of animal and plant cells.
• Each chromosome is made up of the protein histone and a single molecule of deoxyribonucleic acid (DNA).
• Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique.
• Every cell in our body except the sex cells (Sperm and Egg) contain 23 pairs of chromosomes that is 46 chromosomes in total
What are Chromosomes?
Karyotype
• A karyotype is simply a
picture of a person's
chromosomes.
• The chromosomes are
isolated, stained, and
examined under the
microscope.
• The chromosomes in the
white blood cells work
best.
• A picture is then taken
through the microscope.
DNA
• Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the development and functioning of living organisms.
• The main role of DNA in the cell is the long-term storage of information.
• The genome is often compared to a set of blueprints.
• The DNA segments that carry this genetic information are called genes.
Genes
• The instructions necessary to form a new individual are carried in chromosomes in a series of chemicals called GENES.
What are Genes?
• Genes are the working subunits of DNA.
• Each gene contains a particular set of instructions, usually coding for a particular protein or function for making some part of a cell.
Heredity and Genes
• The traits are passed on through genes.
• There are Dominant and Recessive genes.
• Dominant genes overshadow recessive genes and thus can determine the given characteristic.
• The term ‘genotype’ is used for the genetic makeup of an organism i.e. the pair of genes controlling the characteristic.
• The ‘phenotype’ is the actual appearance of that trait.
Alleles
• An Allele is a alternate form of a gene.
• There is a tendency for more people to have Dark hair (D) than Blonde hair (d).
• Thus the Allele for dark hair is dominant over the Allele for blonde hair.
• Dominant Alleles tend to appear more often that recessive genes.
Heterozygous and Homozygous
• An organism can be homozygous dominant, if it carries two copies of the same dominant allele (DD)
• An organism is homozygous recessive, if it carries two copies of the same recessive allele (dd)
• Heterozygous means that an organism has two different alleles of a gene (Dd)
Phenotype - Dark Hair
Genotype - Dd
Phenotype - Blonde Hair
Genotype - dd
Genotype and PhenotypeDark hair (D) is dominant over Blonde hair (d)
d d
D
d
Dd Dd
dddd
The Punnett Square
The Punnett squareis a diagram that is used to predict an outcome of a particular cross.
Make a punnet square for a cross between a homozygous Brown eyed
mother (BB) and a homozygous blue eyed father (bb).
Heredity – Example (2)
b b
B
B
Bb Bb
BbBb
Summary• Chromosomes are thread-like structures found inside the nucleus of animal and
plant cells.
• They are made up of the protein histone and deoxyribonucleic acid (DNA).
• Every cell in our body except the sex cells (Sperm and Egg) contain 23 pairs of chromosomes that is 46 chromosomes.
• The instructions necessary to form a new individual are carried in chromosomes in a series of chemicals called genes.
• There are Dominant and Recessive genes. Dominant genes overshadow recessive genes and thus can determine the given characteristic.
• An Allele is a alternate form of a gene.
• The term ‘genotype’ is used for the genetic makeup of an organism.
• Homozygous means that an organism has two copies of the same allele (DD)
• Heterozygous means that an organism has two different alleles of a gene (Dd)
• The ‘phenotype’ is the actual appearance of that trait.
• The Punnett square is a diagram that is used to predict an outcome of a particular cross.