Inherited Changes Flashcards
Explain the meanings of the terms haploid and diploid.
Haploid - Cell that consists of a single set of chromosomes.
Diploid - Cell that consists of two complete sets of chromosomes.
Explain what is meant by homologous pairs of chromosomes.
A pair of chromosomes that contain the same genes in the same positions and the same position of their centromere.
Explain the need for a reduction division during meiosis in the production of gametes.
Gamete cells contain half the number of chromosomes (23) so that when they fuse, the chromosome number is restored (46). This is done to prevent chromosome number from doubling during fertilisation.
Which genetic process gives rise to production of gametes?
Meiosis
Describe the events of meiosis I.
Prophase I - Centrosomes move to opposite poles of the cell, homologous chromosomes pair up. Crossing over occus here.
Metaphase I - Homologous pair of chromosomes (bivalent) line up at the metaphase plate.
Anaphase I - Bivalent is separating.
Telophase I - Cell divides and two daughter cells are formed.
Describe the events that take place in Meiosis II.
Prophase II - Centrosomes move to opposite poles of the cell.
Metaphase II - Single chromosomes line up along metaphase plate.
Anaphase II - Spindles pull sister chromatids apart to opposite poles of the cell.
Telophase II - Nuclear envelopes reform. Four genetically different daughter cells are produced, each with the haploid number of chromosomes.
Explain the term crossing over and how it results in genetic variation.
During prophase I, there is exchange of genes between non-sister chromatids at the chiasmata which produces different combinations of alleles on the two chromosomes and leads to formation of recombinants.
Explain the term independent assortment and how it results in genetic variation.
During metaphase I, the homologous pair of chromosomes align randomly along the equator. Thus in the daughter cells of meiosis I, there will be a mix of maternal and paternal chromosomes, increasing genetic variation.
Why is random fusion of gametes important?
It increases genetic variation due to the random combination of chromosomes generated.
What is a gene?
A section of DNA that codes for a particular protein.
What is meant by the term locus?
Position of genes on a chromosome.
What is an allele?
Alternative form of a gene.
What is meant by dominant and recessive allele?
Dominant allele - An allele that is always expressed in the phenotype when present, even in the presence of an alternative allele.
Recessive allele - An allele that is only expressed in its homozygous form.
Describe the term ‘linkage’.
Two or more genes are said to be linked if they are found on the same chromosomes and are inherited together because there is no independent assortment.
What is a test cross?
Crossing an individual showing the dominant trait and having an unknown genotype with an individual showing the recessive trait.
What is meant by F1 and F2 generation?
F1 generation - Offspring produced from first filial parents.
F2 generation - Offspring produced from first filial parents.
Define the terms phenotype and genotype.
Phenotype - Observable features of an organism as a result of alleles present.
Genotype - Genetic make-up of an organism in terms of alleles present.
Define the terms homozygous and heterozygous.
Homozygous - Having two identical alleles of a particular gene.
Heterozygous - Having two different alleles of a particular gene.
What is a monohybrid cross?
Cross that involves one pair of contrasting traits.
Define the term sex linkage.
Two or more genes found a sex chromosome (X chromosome) that are inherited together because there is no independent assortment.
Define the term autosomal linkage.
Genes that are inherited together because they are located very close to each other on the same non-sex chromosome.
What is meant by the term ‘codominance’?
Both alleles express equal dominance producing a third phenotype or blend of the parental phenotype in the heterozygous which is different from the homozygous.
Define the term multiple allelism.
Two or more alleles coding for the same gene.
What is dihybrid inheritance?
Kind of genetic inheritance in which parents differ in two traits.
