Genetics Flashcards
What is the role of meiosis in the production of gametes?
Meiosis halves the number of chromosomes in cells, producing genetically different gametes (sperm and egg) with a haploid set of chromosomes, ready for fertilisation.
What happens in meiosis?
Cells divide twice. In the first division, homologous chromosomes separate. In the second, sister chromatids separate. This results in 4 genetically different haploid cells.
What are the advantages and disadvantages of sexual reproduction?
Advantages: creates genetic variation, helps survival in changing environments. Disadvantages: slower, requires two parents.
What are the advantages and disadvantages of asexual reproduction?
Advantages: faster, only one parent needed, all offspring identical. Disadvantages: no variation, all offspring susceptible to same diseases.
Describe the structure of DNA.
DNA is a double helix made of nucleotides, which contain a sugar, phosphate, and a base. Bases pair using complementary base pairing: A with T, C with G, held by hydrogen bonds.
What is the genome of an organism?
The genome is the entire set of genetic material (DNA) in an organism.
What is a gene and what is its role?
A gene is a section of DNA that codes for a specific protein by determining the sequence of amino acids.
How can DNA be extracted from fruit?
Mash fruit, add detergent to break cell membranes, add salt to clump DNA, filter mixture, then add cold ethanol to make DNA precipitate.
Who was Mendel and what did he discover?
Mendel studied pea plants and discovered dominant and recessive traits, forming the basis of genetics. His work was not recognised at first because genes hadn’t been discovered.
Why are there differences in inherited characteristics?
Differences are due to different alleles inherited from parents, which influence characteristics like eye colour or blood type.
Define chromosome, gene, allele, dominant, recessive, and zygote.
• Chromosome: DNA structure carrying genes.
• Gene: Section of DNA coding for a protein.
• Allele: Different version of a gene.
• Dominant: Always expressed if present.
• Recessive: Only expressed if both alleles are recessive.
• Zygote: Fertilised egg cell.
What is the difference between genotype and phenotype?
Genotype is the genetic makeup (e.g., Bb), phenotype is the physical trait shown (e.g., brown eyes).
What are homozygous and heterozygous genotypes?
Homozygous means two of the same allele (e.g., BB or bb). Heterozygous means two different alleles (e.g., Bb).
What are Punnett squares used for?
They predict the possible genotypes and phenotypes of offspring using parent alleles.
Why do some alleles not appear in the phenotype?
If the allele is recessive and a dominant allele is also present, the recessive trait won’t be expressed.
What are pedigree charts and how are they used?
Pedigree charts show inheritance of traits through generations. They help identify carriers, dominant/recessive inheritance, and genotypes.
How is sex determined in humans?
Males have XY chromosomes, females have XX. The sperm determines the sex of the baby.
What are codominance and multiple alleles?
Codominance is when both alleles are expressed (e.g., AB blood type). Multiple alleles means more than two allele options (e.g., A, B, O blood types).
What are sex-linked disorders and how are they inherited?
Sex-linked disorders (like colour blindness) are usually carried on the X chromosome. Males are more likely to have them because they only have one X.
What are polygenic traits?
Traits controlled by multiple genes, such as height or skin colour, leading to continuous variation.
What causes variation in a species?
Variation is caused by genetic differences (alleles/mutations) and environmental factors (like diet or climate).
What is mutation and how does it cause variation?
A mutation is a change in DNA. Most are harmless, but some cause differences in phenotype, increasing variation.
What is the Human Genome Project and what are its benefits?
It mapped all human genes. Benefits include improved diagnosis of genetic disorders, personalised medicine, and better understanding of evolution.
What is meiosis and why is it important? (Short version)
Meiosis is a type of cell division that produces 4 genetically different haploid gametes. It introduces variation and halves the chromosome number so it can be restored during fertilisation.
