Variation and inheritance Flashcards
What is the definition of a gene?
A region of DNA on a chromosome that codes for a characteristic.
What is the definition of an allele?
Different forms of the same gene.
What is the definition of homozygous/true breeding?
An individual with two copies of the same allele present.
What is the definition of heterozygous?
An individual with two different alleles present.
What is the definition of phenotype?
The physical characteristics of an organism.
What is the definition of dominant?
An allele that always shows its effect as a phenotype and masks the presence of the other form.
What is the definition of recessive?
An allele that is masked by the dominant allele i.e. it will only show its effect/show in the phenotype if both alleles are present.
What is the definition of a genotype?
The set of genes (alleles) possessed by an individual.
What does P stand for?
Parent generation
What does F1 stand for?
First (filial) generation
What does F2 stand for?
Second (filial) generation
What is the definition of phenotypic ratio?
The ratio of the appearance of the offspring produced in a genetics cross.
What is the ratio of genotypic ratio?
The ratio of genotypes of the offspring produced in a genetics cross.
What is meant by variation?
Although members of the same species have similar characteristics, they are not identical to each other i.e their is variation (differences) between members of species.
What contributes to variation within species?
Combing genes from two parents, through sexual reproduction, contributes to variation within species.
What are the main two types of variation?
Discrete variation
Continuous variation
What is discrete variation?
Single gene inheritance of characteristics shows discrete variation where measurements fall into distinct groups.
Give an example of discrete variation.
tongue roller/non tongue roller, blood type or leaf shape.
How can discrete variation be displayed?
This information can be displayed in a bar graph.
What is meant by continuous variation?
Polygenic inheritance of characteristics shows continuous variation where there is a range of values between a minimum and maximum.
Give an example of continuous variation.
e.g. human height and milk yield in dairy cows
Why does continuous variation occur?
Continuous variation occurs because several different genes influence the same characteristic.
How can continuous variation be displayed?
Continuous variation can be displayed as a histogram. When a curve is drawn, a bell shape normal distribution curve is produced.
Why are alleles such as tallness in plants said to be tallness?
Alleles such as tallness in plants are said to be dominant because they always show up in the phenotype of the offspring even though both types of the alleles are present.
Why are allele for dwarfness in plants said to be recessive?
Alleles for dwarfness in plants are said to be recessive because they only show up in the phenotype if the organism inherits both of them.
What types of letters are dominant and recessive given?
Dominants are usually given the capital letter e.g. T while recessive alleles are given lower case of the same letter.
Why do actual or observed ratios in offspring not always match the predicted ratios?
Fertilisation is a random process.
The numbers of organisms in the cross are too small.
What are family tree diagrams used for?
Family tree diagrams can be used to show the inheritance of characteristics over generations.
Give an example of a use of family trees?
For example, they are useful in studying human families, especially where genetic disorders such as cystic fibrosis or haemophilia are known to occur.
