topic 3 Flashcards
Name the gametes in humans.
Sperm (male) and egg (female)
What happens to the DNA in a cell before the first division in meiosis?
The DNA is copied so each chromosome has two identical chromatids.
What is the advantage of having genetic variation in a population?
Increases survival chances — some individuals may cope better with disease or changes in the environment.
Give a reason why sexual reproduction can take more time than asexual reproduction.
Mates need to be found, which takes time and energy.
What is a single nucleotide made of?
Phosphate + sugar + base (e.g. A, T, C, or G)
What is meant by the term ‘double helix’?
The structure of DNA — two strands twisted around each other like a spiral staircase.
What is the purpose of mixing fruit with detergent when extracting DNA?
It breaks open cell membranes to release the DNA.
What effect does ice-cold alcohol have on a solution containing DNA?
DNA becomes visible as it clumps together (precipitates).
itll look like white stringy precipitate
Proteins are made up of ______ joined together in a chain.
Amino acids
How do DNA bases code for specific amino acids?
Each group of 3 bases (triplet) codes for one amino acid.
Name the enzyme that joins RNA nucleotides to make mRNA.
RNA polymerase
How can a mutation in non-coding DNA affect the phenotype of an organism?
It might change how a gene is turned on/off, affecting protein production.
What did Mendel do to study the inheritance of height in pea plants?
He crossbred tall and short pea plants and recorded the height of offspring over generations.
What were three conclusions Mendel made from his experiments?
1) Inheritance is controlled by units (genes), 2) Genes are passed unchanged, 3) Some traits are dominant.
What does homozygous mean?
Having two identical alleles (e.g. TT or tt)
What does heterozygous mean?
Having two different alleles (e.g. Tt)
What is monohybrid inheritance?
when a single trait is passed down generations by one gene (eg dimples)
What is the probability that a baby will have the XX combination of chromosomes?
50%
How are carriers shown on a pedigree chart?
Half-shaded circle (female) or square (male)
Why are there more genes on the X chromosome than the Y chromosome?
The X is larger and carries more genes.
Why are males more likely to show recessive sex-linked disorders?
They only have one X chromosome, so no second copy to mask the recessive allele.
What do you call someone with one copy of a recessive allele for a disorder?
Carrier
What is codominance?
When both alleles are expressed equally in the phenotype.
What blood group does a person with genotype IᴬIᴼ have?
Blood group A
What causes genetic variation in a species?
Mutations, meiosis (crossing over), and sexual reproduction.
What is an acquired characteristic?
A trait gained during life, not inherited (e.g. a scar)
Give three applications of the Human Genome Project.
1) Identify genes linked to disease, 2) Personalised medicine, 3) Study human evolution
Give three drawbacks of reading someone’s genome.
1) Privacy issues, 2) Risk of discrimination, 3) May cause stress if at risk of illness
describe transcription (PART 1 of protein synthesis)
Transcription occurs in the nucleus, where the DNA double helix unwinds, exposing the template strand. RNA polymerase binds to the non-coding region of the DNA and synthesizes mRNA by adding complementary RNA bases to the DNA strand. During this process, thymine (T) in the DNA is replaced by uracil (U) in the mRNA. The mRNA then detaches from the DNA and moves out of the nucleus to the ribosomes for translation.
describe translation (PART 2 of protein synthesis)
translation happens at the ribosomes where mRNA is read in triplets (codons) each coding for an amino acid. tRNA molecules bring amino acids, matching their anticodons to the mRNA codons. the ribosome links amino acids with peptide bonds, forming a polypeptide chain which then folds into a protein
