11 Inheritance
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Define Inheritance
The transmission of genetic information from generation to generation.
Define Chromosome
A thread-like structure of DNA, carrying genetic information in the form of genes.
Define Gene
A length of DNA that codes for a protein.
Define Allele
A version of a gene.
Describe the inheritance of sex in humans
Sex is determined by an entire chromosome pair. Females have the XX sex chromosomes whilst males have XY. Father determines sex of child since he is the only one that can pass on the Y chromosome. Half of the sperm will have X chromosome and the other half will have Y. Depending on the sperms chromosome, the sex will be determined.
Define a Haploid nucleus
A nucleus containing a single set of unpaired chromosomes, for example in gametes.
Define a Diploid nucleus
A nucleus containing two sets of chromosome, for example in body cells.
How many chromosomes in a human haploid gamete cell?
23
Define Mitosis
Nuclear division giving rise to genetically identical cells.
What occurs before mitosis?
The exact duplication of chromosomes.
Role of Mitosis
Used for growth as they produce new cells, repair to replace damaged or dead cells, replacement of cells and asexual reproduction as it produces offspring identical to the parent.
Define Meiosis
A reduction division in which the chromosome number is halved from diploid cells. Gives rise to cells that are genetically different. Used to produce gametes. Increases genetic variation of offspring by forming new combinations of maternal and paternal chromosomes every time a gamete is made.
Define Genotype
The genetic make-up of an organism in terms of the alleles present.
Define Phenotype
The observable features of an organism.
Define Homozygous
Having two identical alleles of a particular gene.
How does pure-breeding occur?
Two identical homozygous individuals breeding together.
Define Heterozygous
Having two different alleles of a particular gene.
Define Dominant
An allele that is expressed if it is present.
Define Recessive
An allele that is only expressed if it is present.
Define Variation
Differences between individuals of the same species.
Define Phenotypic variation
The differences in features between individuals of the same species caused by both genes and the environment.
Define Genetic variation
Differences in features caused by differences in genes.
Differences between Continuous and Discontinuous variation
Continuous: results in a range of phenotypes between two extremes (E.g. height). Discontinuous: results in a limited number of phenotypes with no intermediates. Mostly caused by genes alone (E.g Blood groups).
Define Mutation
A change in a gene or chromosome.