Inheritance and selection Flashcards
What is meant by genotype?
The genetic make up of an organism that describes all the alleles that the organism contains, i.e. Bb
What is meant by phenotype?
The observable characteristics of an organism. It is the result of the interaction between the expression of the genotype and the environment.
What is a gene?
A section of DNA that is a sequence of nucleotide bases, that codes for a single characteristic of an organism.
What is an allele?
One of the different forms of the gene.
What is meant by the gene locus?
The position of the gene on the chromosome.
What are homologous chromosomes?
A pair of chromosomes that an individual possesses, one from the mother, one from the father.
What is meant by the term homozygous?
Both alleles from both chromosomes are the same.
What is meant by the term heterozygous?
The alleles on the two different chromosomes are different.
What is an individual with two dominant alleles called?
Homozygous dominant.
What is an individual with two recessive alleles called?
Homozygous recessive.
What is meant by ‘dominant allele’?
An allele that will always be expressed in the phenotype of the individual.
What is meant by ‘recessive allele’?
An allele that will not be expressed in the phenotype of the individual if a dominant allele is present in the genotype.
What is meant by the F1 generation?
The first set of offspring from the genetic cross.
What is meant by the F2 generation?
The offspring of the crossing of the F1 generation.
How many pairs of chromosomes do humans have?
23
What are the human sex chromosomes/gametes?
Females = XX Males = XY
What does the term sex-linked refer to?
Any gene that is carried on either the X or Y chromosome is said to be sex-linked.
What is the effect of the Y chromosome on sex linked disorders?
The Y chromosome is shorter than the X chromosome, so if the gene is carried on the X chromosome, the male wont have 2 alleles for it and only one due to the length.
Why will characteristics controlled by a recessive allele often occur more frequently in males?
Because a male will only need one recessive allele rather than two to be expressed as there is no dominant allele on the other chromosome.
What is an example of a sex-linked disorder?
Haemophilia (caused by a recessive allele).
What is a carrier?
When an individual possesses the particular allele without expressing it in the phenotype.
What is the family tree diagram called?
A pedigree chart.
What is a male represented by in a Pedigree Chart?
A square.
What is a female represented by in a Pedigree Chart?
A circle.
What does shading mean in a Pedigree Chart?
Presence of a characteristic.
What does a dot mean in a Pedigree Chart?
Carrying.