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DNA, or deoxyribonucleic acid, is a biomolecule, which serves as the blueprint of living organisms. A gene is a segment of DNA that is passed down from parents to offspring through the packaged units called chromosomes. The genetic transmission of traits is referred to as heredity.
See the fact file below for more information on the DNA and Inheritance or alternatively, you can download our 28-page DNA and Inheritance worksheet pack to utilise within the classroom or home environment.
Key Facts & Information
Fundamental Concepts of the Human Genome
- In 1953, James D. Watson and Francis Crick discovered the double helix structure of the DNA molecule. The human genome is made up of 3.2 billion bases of DNA. Other genomes of living organisms vary in size.
- Most of the human genome is made of noncoding DNA, which is often called “junk DNA”.
- A human genome is 98% identical to a chimpanzee genome. Compared to gorillas with 97% similarity, humans are closer to chimpanzees and random human strangers are on average 99.5% identical.
- Despite its earlier discovery, the first complete human genome was only decoded in 2003 and was published four years later. It was James Watson, CEO of the Celera Genomics whose genome was first sequenced through the U.S. government’s Human Genome Project.
- Like all other living animals, a human genome is made up of long polymers of DNA. In the form of chromosomes in every human cell, these polymers are maintained in duplicate copy.
DNA: The Building Blocks
- The chemical comprising the human genome is called DNA or deoxyribonucleic acid. It contains the four building blocks or bases known as nucleotides: Adenine (A), Cytosine (C), Guanine (G) and Thymine (T), wherein A always pairs with T, and G always pairs with C. The order or sequence of these bases dictates the instructions in the genome. In RNA, or ribonucleic acid, thymine (T) is replaced by uracil (U).
- Except for gametes or sex cells (ovocytes for females and sperm cells for males) and red blood cells, every cell in the body contains a complete copy of our genome.
- DNA is a two-stranded molecule with a unique double-helix shape, like a spiral ladder. The rungs or the ladder of the DNA is formed when complementary bases are pair together. Each base pair is joined by hydrogen bonds.
- Some parts of human DNA are genes that carry instructions for making proteins. Proteins are long chains of amino acids, which help in building an organism. It can be divided into codons or sets of three bases.
- Each strand of DNA is separated during replication. DNA replication is the process by which the cell duplicates and is divided into new daughter cells through the process of either mitosis or meiosis. The base pairs are broken by an enzyme known as DNA helicase separating the strands and forming the Y-shaped replication fork. Once separated, a primer generated by DNA primase binds to the 3’ end of the strand (with a hydroxyl group attached). Through the process of elongation, a new strand is created by the enzymes called DNA polymerases.
- Each cell has a nucleus wherein DNA is packed into thread-like structures called chromosomes.
- Humans have 23 pairs of chromosomes wherein one chromosome from each pair is inherited from the mother and the other pair from the father, for a total of 46 chromosomes.
- Both males and females have 22 pairs of chromosomes called autosomes. The 23rd pair, known as the sex chromosomes, differ between the two. Males have XY chromosomes, while females have XX chromosomes.
- Like most animals and unlike plants, humans are diploid, which means they only have two sets of chromosomes.
- In the animal and plant kingdoms, the number of chromosomes varies from 2 (roundworms) up to 254 (hermit crab) chromosomes.
- A child inherits half of his/her DNA from his/her biological mother and half from his/her biological father. This means brothers and sisters share 50% of each other’s DNA and 25% of the grandparent’s DNA. This explains how characteristics are passed from parents to offspring or from generation to generation.
- In 1865, a monk and scientist later named the father of modern genetics, Gregor Mendel, published his work detailing his experiments on pea plants regarding inheritance and characteristics. Mendel was the first to correctly understand the process of inheritance from parents to offspring disproving the blending theory of scientists during his time.
- After Mendel’s experiments on pea plants, he came up with the following conclusion: (1) Each trait is passed on unchanged to offspring through alleles. (2) An offspring inherits one allele from each parent for each characteristic. (3) Some alleles may not be expressed in an offspring but can still be passed to succeeding generations.
- Mendel came up with his Laws of Inheritance including the Law of Segregation and Law of Independent Assortment.
- According to Mendel, alleles are a certain form of gene passed from parents to offspring. A combination of two alleles received from each parent is called a genotype, while the physical expression of the genotype is called phenotype.
- A genotype with two different alleles is called heterozygous (Bb), while a genotype with two of the same alleles is called homozygous (BB and bb).
- Sometimes, certain alleles are influenced by the environment changing the phenotype of a child.
- The possible genotype and phenotype of an offspring can be determined using a Punnett Square.
If the father has blue eyes while the mother has brown eyes, both of them will pass alleles to their child but certain alleles have the ability to dominate the other. The child received the brown-eye alleles from the mother because the father’s blue-eye alleles are recessive. In genotype, the mother’s dominant brown eyes can be represented with B, while the father’s recessive brown eyes is written with b. Thus, the child’s genotype is Bb.
- Therefore, genetic inheritance is the process by which genetic information is passed on from parent to offspring. This explains how and why members of the same family tend to have similar characteristics.
- Genetic mutations may occur when DNA changes, altering the genetic instructions. Mutations can be caused by exposure to chemicals such as cigarette smoke, medicine and alcohol. In addition, mutations may also occur when DNA is not copied properly during cell division.
- Mutation in a single gene can cause certain medical conditions that may be passed from parent to child.
- Such genetic conditions can be inherited in three different ways, including autosomal recessive inheritance, autosomal dominant inheritance, and X-linked inheritance.
- Genetic conditions inherited through an autosomal dominant pattern are type 1 neurofibromatosis, tuberous sclerosis, Huntington’s disease and autosomal dominant polycystic kidney disease or ADPKD. This means only one parent needs to carry the mutation for the 50% chance that it will be passed to the couple’s children.
- Some conditions may only be inherited when both parents are carriers of the faulty gene through the autosomal recessive pattern. Conditions include cystic fibrosis, sickle cell anemia, thalassemia and Tay-Sachs disease.
- Unlike the autosomal dominant pattern, the autosomal recessive pattern needs a child to inherit both copies of his/her parents’ faulty gene to have the condition. If a child only inherits the gene from one parent, s/he will be a carrier of the condition but will not have the condition.
- Some conditions like hemophilia, Duchenne muscular dystrophy and fragile X syndrome are passed through X-linked inheritance. X-linked mutations are inherited by females, making them carriers, while males inherit the mutation from their mothers and develop the condition. In short, when a mother is a carrier of an X-linked mutation, each daughter has a 50% chance of becoming a carrier and each son has a 50% chance of inheriting the condition.
DNA and Inheritance Worksheets
This is a fantastic bundle which includes everything you need to know about DNA and Inheritance across 28 in-depth pages. These are ready-to-use DNA and Inheritance worksheets that are perfect for teaching students about the DNA, or deoxyribonucleic acid, which is a biomolecule, which serves as the blueprint of living organisms. A gene is a segment of DNA that is passed down from parents to offspring through the packaged units called chromosomes. The genetic transmission of traits is referred to as heredity.
Complete List Of Included Worksheets
- DNA and Inheritance Facts
- DNA Structuring
- Make it Double
- Decoding DNA
- Base Pairing
- Genetic Codes
- Mendelian Profile
- Genetic Mystery
- Passing Mutations
- The Human Genome Project
- Thanks to Heredity!
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Link will appear as DNA and Inheritance Facts & Worksheets: https://kidskonnect.com - KidsKonnect, July 26, 2018
Use With Any Curriculum
These worksheets have been specifically designed for use with any international curriculum. You can use these worksheets as-is, or edit them using Google Slides to make them more specific to your own student ability levels and curriculum standards.