Chapter 19 - Heredity Flashcards
What are alleles?
Alleles are different forms of the same gene that occupy the same relative positions (gene loci) on a pair of homologous chromosomes.
Define Monohybrid inheritance.
It is the inheritance of 1 characteristic that has 2 contrasting forms.
Define dominant allele.
It is an allele that expresses itself and gives the same phenotype in both homozygous and heterozygous conditions.
Define recessive allele.
It is the allele that only expresses itself in the phenotype in the homozygous conditions.
Define codominance and give an example.
It is a condition where both alleles express themselves equally in the phenotype. E.g. IA and IB alleles in blood group
Define genotype.
It is the genetic make-up of an organism.
Define phenotype.
It is the expressed trait in an organism. It is influenced by its genotype and the environment.
How can genotype of an organism with dominant trait be tested for? What are the possible results?
Use a test cross. Cross the organism with a homozygous recessive organism. If the organism is homozygous dominant, all offspring should show the dominant trait. If the organism is heterozygous, half the number of offspring should show the dominant trait, and the remaining show the recessive trait.
What is incomplete dominance? Give an example.
It is when 2 alleles both refuse to express themselves, and the intermediate trait is shown. For example, when a black and white organism mate, their offspring might be grey.
What are autosomes?
Autosomes are chromosomes in cells other than the sex chromosome.
What is the makeup of chromosomes of each cell?
22 pairs of autosomes and 1 pair of sex chromosomes.
How is the gender of a baby determined?
Female gametes contain only the X chromosome, while male gametes contain either X or Y chromosome. There is an equal chance that the offspring could be male of female.
XX: female
XY: male
What are multiple alleles?
If a gene for a particular trait exists in more than 2 alleles.
What are 3 differences between continuous variation and discontinuous variation?
1) CV is controlled by the additive effect of many genes, while DV is controlled by one or a few genes
2) CV has a range of phenotypes while DV has clear-cut phenotypes with no intermediate forms
3) CV can be affected by environmental conditions while DV is not affected by environmental conditions.
List 3 examples of continuous variation.
Skin color, height, weight
List 3 examples of discontinuous variation.
Blood group, gender, eye color
Define mutation.
It is a sudden random change in gene structure or chromosome number.
Why do mutations occur?
Mutation occurs as a result of error during the replication if the gene or chromosome. Somatic (body cell) mutations cannot be inherited, but if mutation occurs in cells that give rise of gametes, it may be inherited by the next generation.
What is the difference between chromosome and gene mutation?
Chromosome mutation is the change in structure of number of chromosomes, causing diseases like Down syndrome, while gene mutation is the change in structure of DNA, producing variation between individuals as it results in new alleles of genes. It causes diseases like albinism.
Discuss about down syndrome.
It is a chromosomal number mutation. People with this syndrome has 47 chromosomes instead of 46, with the extra chromosome at chromosome number 21. It is causes by the defective stages of meiosis during anaphase I/anaphase II.
Discuss about sickle-cell anemia.
It is a gene mutation. The gene that codes for normal haemoglobin is mutated to form abnormal haemoglobin. The abnormal haemoglobin causes red blood cells to be sickle shaped. They carry less oxygen around the body, and tend to clump together. Although homozygous recessive dies young, but heterozygous survives better in malaria prone areas.
What are mutagenic agents?
Since the rate of spontaneous mutation is usually very low, mutagenic agents(mutagens) greatly increases the rate of mutation.
List 2 examples of mutagens.
1) radiation (UV Light, alpha and beta radiation)
2) chemicals (mustard gas, formaldehyde)
How does variation and competition lead to natural selection?(3)
1) mutation provides new alleles to the gene pool for natural selection to act on
2) genetic variation is important to help organisms adapt and survive in changing environments
3) competition arise due to differences in the same species, leading to differential survival and reproduction. nature selects varieties of organisms that are more resistant to diseases and better adapted to changes in the environment.
