Term 2: Flashcards
What does the term ‘heritable’ refer to?
Features determined by genes (rather than the environment) and therefore passed on to offspring
Heritable traits are typically influenced by genetic factors.
Define ‘homologous chromosomes’.
A pair of chromosomes, one maternal and one paternal, that have the same gene loci and therefore determine the same features
They are not necessarily identical as they may have different alleles.
What is a ‘ratio’ in genetic terms?
A measure of the relative size of two classes that is expressed as a proportion
What are ‘sex-linked’ genes?
Any gene that is carried on either the X or Y chromosome
What does ‘linkage’ refer to in genetics?
The situation where two or more genes are carried on the same autosome
Define ‘autosome’.
A chromosome which is not a sex chromosome
What is ‘epistasis’?
This arises when the allele of one gene affects or masks the expression of another in the phenotype
What does the Hardy-Weinberg Principle predict?
The proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to next provided five conditions:
* No mutations
* Population is isolated
* No natural selection (alleles are equally likely to be passed on)
* Large population
* Mating is random
What is a ‘gene pool’?
All the different alleles of all the genes of all the individuals in a population at any one time
Define ‘allelic frequency’.
The number of times an allele occurs within the gene pool in a population, relative to all others at the same locus
What is ‘discontinuous variation’?
Distinct forms with no intermediate types
What is ‘continuous variation’?
No distinct categories - likely to obtain a bell-shaped curve known as a normal distribution curve
What is a gene?
Section of DNA on a chromosome that controls a feature by coding for formation of one or more specific polypeptides or a functional RNA (including rRNA and tRNA).
What is a locus?
The specific linear position of a particular gene on a certain chromosome.
What are alleles?
Alternative forms of a particular gene with different base sequences, and therefore different codes.
What does homozygous mean?
Situation or organism in which paired alleles are the same.
What does heterozygous mean?
Situation of organism in which paired alleles are different.
What is a dominant allele?
An allele that expresses itself in the phenotype in heterozygous organisms.
What is a recessive allele?
An allele that does not express itself in the phenotype in heterozygous organisms.
What is co-dominance?
Alleles which both contribute to the phenotype (i.e. produce a blended effect) in the heterozygous condition.
What are multiple alleles?
If there are more than two alleles for each gene in the gene pool.
Only 2 chromosomes in a homologous pair so only 2 of the three or more alleles can be present in a single organism.
What is a pure-breeding strain?
Group of organisms in which a certain characteristic is unaltered for generations, indicating that organisms are homozygous for that feature.
What is monohybrid inheritance?
Inheritance of a single pair of alleles.
What is dihybrid inheritance?
Inheritance of two pairs of alleles.
What is a haploid cell?
Cell or nucleus containing single, unpaired chromosomes.
What is a diploid cell?
Cell or nucleus containing pairs of homologous chromosomes.
What is phenotype?
The observable or biochemical characteristics of an organism, resulting from both its genotype and the effects of the environment.
What is genotype?
The combination of alleles present within the cells of an organism.
What is a population?
A group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed.
This definition emphasizes the potential for interbreeding among organisms of the same species within a defined area.
Define community in an ecological context.
The organisms of all species that live in the same area.
A community includes multiple species interacting within a shared environment.
What is a habitat?
The place where an organism normally lives.
A habitat provides the necessary resources and conditions for an organism’s survival.
What is meiosis?
A type of nuclear division in which the number of chromosomes is halved.
Meiosis is essential for sexual reproduction, producing gametes with half the genetic material.
What is a gamete?
Reproductive (sex) cell that fuses with another gamete during fertilisation.
Examples of gametes include sperm and egg cells.
Define diploid.
Cell or nucleus containing pairs of homologous chromosomes (two sets of chromosomes).
Diploid organisms have two complete sets of chromosomes, one from each parent.
Define haploid.
Cell or nucleus containing single, unpaired chromosomes (a single copy of each chromosome).
Haploid cells are typically gametes, which have only one set of chromosomes.
What are homologous chromosomes?
A pair of chromosomes, one maternal and one paternal, that have the same gene loci and therefore determine the same features.
Homologous chromosomes may have different alleles for the same gene.
What is crossing over?
The process whereby a chromatid breaks during meiosis and rejoins to the chromatid of its homologous chromosome so that their alleles are exchanged.
Crossing over increases genetic diversity in gametes.
What are chiasmata?
A point at which paired chromosomes remain in contact during the first metaphase of meiosis and at which crossing over and exchange of genetic material occur between the strands.
Chiasmata are crucial for genetic recombination during meiosis.
Define recombination.
The rearrangement of genetic material, especially by crossing over in chromosomes.
Recombination contributes to genetic variation in offspring.
What is independent assortment?
The alleles of two (or more) different genes get sorted into gametes independently of one another.
This process occurs during metaphase in meiosis, leading to genetic variation.
Fill in the blank: During the formation of gametes, each gamete receives just one gene copy, which is selected _______.
randomly.
Random selection of gene copies contributes to genetic diversity in gametes.
What is independent segregation?
Each pair of alleles segregates independently of the other pairs and all possible combinations of alleles can occur in the resulting gametes.
This principle is a fundamental aspect of Mendelian genetics.
