Genetic Diagrams and Inheritance - Paper 1 Flashcards
Describe the results of the genetic cross performed by Gregor Mendel.
Mendel found that when he bred red-flowered plants with white-flowered plants, all the offspring produced red flowers.
If he bred these plants with each other, most of the offspring had red flowers, but some had white.
Describe Mendel’s observation that was the basis for understanding of genetic inheritance.
One of Mendel’s observations was that the inheritance of each characteristic is determined by ‘units’ that are passed on to descendants unchanged. We now know these as genes.
Define chromosome
Chromosomes are long strands of DNA, made up of many genes, contained in a cell’s nucleus.
Define gene
A gene is a small section of DNA on a chromosome, that codes for a particular sequence of amino acids, to make a specific protein.
Define allele
Alleles are different forms of the same gene.
Explain the difference between dominant and recessive alleles.
Dominant alleles always express themselves no matter their partner.
Recessive alleles must be partnered with another recessive allele to express itself.
Explain the difference between homo- and heterozygous.
In homozygous genotypes, the two alleles for a particular characteristic are the same.
In heterozygous genotypes, the two alleles for a particular characteristic are different.
Explain the relationship between genotype and phenotype.
The genotype is the collection of alleles that determine characteristics and can be expressed as a phenotype.
Most phenotypic features are the result of multiple genes rather than single gene inheritance.
Explain the relationship between gametes and zygotes.
A zygote is the diploid cell formed from the fusion of two haploid gametes.
Define monohybrid inheritance
Monohybrid inheritance describes the transmission of a single gene from parents to offspring.
Recall the format of genetic diagrams and Punnett squares.
Define pedigree chart
A family pedigree chart is a family tree diagram which shows the inheritance of a genetic condition in a family.
Recall the symbols used on a family pedigree chart.
Recall the male and female sex chromosomes.
Females: XX
Males: XY
Define codominant
Codominant alleles are both expressed in the same phenotype.
Describe the inheritance of the ABO blood groups.
The gene controlling blood group has 3 alleles. IA and IB are codominant, while IO is recessive.
Explain how sex-linked genetic disorders are inherited.
If a gene is contained on the part of the X chromosome that is missing from the Y chromosome, men only have one allele for that gene.
If the allele on the X chromosome codes for a disorder, the man will always have the disorder because there isn’t another allele on the Y chromosome to mask the effect of the allele.
Describe the causes of variation that influence phenotype.
Genetic variation - different characteristics as a result of mutation and sexual reproduction.
Environmental variation - different characteristics caused by an organism’s environment (acquired characteristics).
What does the mapping of the whole human genome allow us to do?
- Search for genes linked to different types of disease.
- Understand inherited disorders and their treatment.
- Trace human migration patterns from the past.
How do gene mutations tend to affect the phenotype?
Most genetic mutations have no effect on the phenotype, some mutations have a small effect on the phenotype and, rarely, a single mutation will significantly
affect the phenotype.
