Inheritance Flashcards
All 32 cards in this deck
What is an allele?
A different version (form) of the same gene.
What does it mean if an allele is dominant?
Only one copy is needed for it to be expressed in the phenotype.
What does homozygous mean?
Having two identical alleles of a gene.
e.g. HH or hhTrue or false? Two people with the same phenotype must have the same genotype.
False. A dominant phenotype can come from HH or Hh.
What is a zygote?
The single cell formed when two gametes fuse at fertilisation.
What phenotype ratio is expected from a cross between two heterozygous parents (Hh × Hh)?
3 dominant : 1 recessive (genotypes 1 HH : 2 Hh : 1 hh).
In a family pedigree, two unaffected parents have an affected child. What does this show about the allele and the parents' genotypes?
The allele is recessive, and both parents are heterozygous (carriers, Hh).
True or false? In a pedigree, an unaffected child of a parent with a recessive disorder must have inherited the dominant allele.
True. Unaffected offspring must have inherited the dominant allele from one parent.
What are the sex chromosomes of a human male and a human female?
Male XY, female XX.
What ratio of male to female offspring is predicted by a genetic diagram of XX × XY?
50 : 50 (1 : 1) — a 50% chance of each sex.
Which parent determines the sex of a human offspring, and why?
The father — his sperm carries either an X or a Y chromosome, while all eggs carry X.
What is polygenic inheritance?
A characteristic controlled by several genes rather than a single gene.
True or false? Most human phenotypic features are controlled by a single gene.
False. Most phenotypic features are the result of multiple genes.
What two things produce genetic variation in a species?
Mutation and sexual reproduction (which gives new combinations of alleles).
What is an acquired characteristic?
A characteristic caused by the organism's environment or lifestyle, not by its alleles.
Give two environmental factors, other than inherited alleles, that influence a person's mass.
Diet / food intake and exercise / activity.
True or false? Acquired characteristics caused by the environment can be passed on to offspring.
False. Only characteristics determined by alleles in the gametes are inherited.
What was the Human Genome Project?
A project that sequenced the order of the bases in the whole human genome.
Give two outcomes of the Human Genome Project, other than sequencing the bases.
Mapping/finding the genes and their locations on chromosomes; identifying alleles and mutations. (Also: finding the functions of proteins.)
Give two medical applications of the Human Genome Project.
Genetic testing / prediction of disease risk, and personalised (tailor-made) medicines or new treatments.
Give one benefit and one drawback for an individual of learning from genome testing that they may develop a disease.
Benefit: they can modify their lifestyle or take preventative medicine to reduce the risk. Drawback: knowing a disease could develop may cause stress or discrimination by insurers/employers.
What is a mutation?
A change in the sequence of DNA bases.
How does a mutation lead to genetic variation within a population?
It changes the DNA base sequence, producing a different allele of the gene, which can affect the phenotype.
What are the three possible effects of a mutation on the phenotype?
Most have no effect; some have a small effect; rarely, a single mutation significantly affects the phenotype.
True or false? An insertion, deletion or substitution of DNA bases all count as mutations.
True. Each changes the sequence of DNA bases.
What is a genotype?
The alleles an organism has for a particular gene, written as letters.
e.g. BbWhat is a phenotype?
The observable characteristics of an organism, e.g. eye colour. They come from its genotype, often also affected by its environment.
What is meant by a heterozygous genotype?
One in which the two alleles of a gene are different from each other, e.g. Hh (one dominant and one recessive allele).
When is a recessive allele expressed in the phenotype?
Only when two copies are present (homozygous recessive, e.g. hh), so there is no dominant allele to mask it.
What is a chromosome?
A structure made of one very long DNA molecule, tightly coiled, that carries many genes. In eukaryotic cells chromosomes are in the nucleus.
What is a carrier of a genetic disorder?
A person with one copy of the recessive allele for the disorder (heterozygous, e.g. Ff). They do not have the disorder but can pass the allele on.
What causes most of the variation in a phenotype?
A mixture of genetic and environmental factors acting together, e.g. skin colour depends on both your alleles and your exposure to sunlight.