Genetics
Genetics is the study of heredity, or how certain features pass from parents to their offspring.
Offspring are not usually exactly the same as their parents. For example, their eye colour or height could be different.
Genes are the basic units of heredity.
Genes are located inside cells.
Threadlike structures called chromosomes carry the genes.
Chromosomes are made up of DNA. Genes are short sections of DNA.
In human beings most cells have 23 pairs of chromosomes, or 46 in total. The sex cells (gametes), sperm cells and egg cells have one set of 23 chromosomes.
In 1900 scientists began to explain the theory of evolution including an English scientist named Charles Darwin. He described how species adapt to their environments and how new species form.
Asexual Reproduction
Sexual Reproduction
Offspring are not usually exactly the same as their parents. For example, their eye colour or height could be different.
Genes are the basic units of heredity.
Genes are located inside cells.
Threadlike structures called chromosomes carry the genes.
Chromosomes are made up of DNA. Genes are short sections of DNA.
In human beings most cells have 23 pairs of chromosomes, or 46 in total. The sex cells (gametes), sperm cells and egg cells have one set of 23 chromosomes.
In 1900 scientists began to explain the theory of evolution including an English scientist named Charles Darwin. He described how species adapt to their environments and how new species form.
Asexual Reproduction
- Definition: A type of reproduction involving a single parent, producing offspring that are genetically identical to the parent.
- Characteristics:
- No gametes involved.
- Offspring are clones (no genetic variation).
- Common in unicellular organisms and some plants and animals.
- Examples:
- Binary Fission: Bacteria splitting into two identical cells.
- Budding: Yeast forming a new individual as a bud from the parent.
- Runners: Strawberry plants producing new plants via horizontal stems.
- Fragmentation: Starfish regenerating from a piece of their body.
Sexual Reproduction
- Definition: A type of reproduction involving two parents, where male and female gametes fuse to form a zygote, producing genetically unique offspring.
- Characteristics:
- Genetic variation in offspring.
- Requires gametes (e.g., sperm and egg in animals, pollen and ovules in plants).
- Examples:
- Humans and other animals (internal fertilisation).
- Flowering plants (pollination and fertilisation).
Inheritance
Genetic Variation
Dominant and Recessive Traits
Punnett Square
- Definition: The passing of genetic information from parents to offspring through genes.
- Genes:
- Segments of DNA located on chromosomes.
- Control specific traits (e.g., eye colour, height).
- Chromosomes:
- Found in the nucleus of cells.
- Humans have 23 pairs (46 total).
Genetic Variation
- Definition: Differences in DNA sequences among individuals, leading to diversity in traits.
- Sources of Variation:
- Sexual Reproduction: Mixing of genetic material from two parents.
- Mutation: Changes in the DNA sequence.
- Importance:
- Allows adaptation to environmental changes.
- Promotes survival of species.
Dominant and Recessive Traits
- Dominant Trait: Expressed even if only one allele is present (e.g., brown eyes).
- Recessive Trait: Expressed only if both alleles are recessive (e.g., blue eyes).
Punnett Square
- Definition: A tool used to predict the probability of traits in offspring.
- Example: Cross between two heterozygous parents (Bb × Bb):
- Probability of brown eyes = 75%, blue eyes = 25%.
Flashcards-
Q: What is asexual reproduction?
A: Asexual reproduction is a type of reproduction where one parent produces offspring that are genetically identical to itself.
Q: Give an example of asexual reproduction.
A: Examples include binary fission in bacteria, budding in yeast, and runners in strawberry plants.
Q: What is sexual reproduction?
A: Sexual reproduction involves two parents, where male and female gametes fuse to produce genetically unique offspring.
Q: How do asexual and sexual reproduction differ?
A:
- Asexual: One parent, no genetic variation.
- Sexual: Two parents, genetic variation in offspring.
Q: What is a gene?
A: A gene is a segment of DNA that determines a specific characteristic or trait in an organism.
Q: What is inheritance?
A: Inheritance is the process by which genetic information is passed from parents to offspring.
Q: What is genetic variation?
A: Genetic variation refers to differences in DNA sequences among individuals, leading to differences in traits.
Q: How is genetic variation created?
A: Through sexual reproduction (mixing of genes) and mutations (changes in DNA).
Q: What are dominant and recessive traits?
A:
- Dominant: Expressed with one dominant allele (e.g., brown eyes).
- Recessive: Only expressed with two recessive alleles (e.g., blue eyes).
Q: What is a Punnett square used for?
A: A Punnett square predicts the possible genetic outcomes of offspring based on the parents' genotypes.
Q: What is an example of a dominant trait?
A: Brown eyes or dark hair.
Q: What is an example of a recessive trait?
A: Blue eyes or blonde hair.
Q: Why is genetic variation important?
A: It allows species to adapt to changing environments and increases survival chances.
Q: Name an inherited genetic disorder.
A: Cystic fibrosis or sickle cell anaemia.
