Topic 14:inheritance Flashcards
Definition of trait
the characteristic of an organism coded by a gene
how are different phenotypes inherited through DNA
we express a certain phenotype because we inherit genes from our parents that code for this phenotype
how many chromosomes are there in a typical human cell
46 chromosomes
how many chromosomes are there in a human sex cell(gamete)
23 chromosomes
what is the definition of homologous chromosomes
A pair of chromosomes which have similar shape, size and set of gene loci. (no need state this)One chromosome is from the male parent and the other is from the female parent
definition of locus
the place on chromosome where the specific gene is located
what is plural of”locus”
loci
definition of allele
different forms of the same gene,occupying the same locus on a pair of chromosomes
definition of genotype
the combination of genes in an organism
definition of multiple alleles
a gene which exists in more than 2 alleles
definition of co-dominant alleles
different alleles controlling the same trait, which are both expressed when genotype is heterozygous
what are the sex chromosomes in a sex cell for male and female respectively?
male->XY
Female->XX
definition of mutation
a sudden random change in the structure of a gene or in the chromosome number
other than occasional error in DNA replication(which is called spontaneous mutation),mutations can also be caused by exposure to other mutagens such as?
-Ionising radiation e.g. X-ray
-UV light
-chemical mutagens like tar,formaldehyde
what are the 2 types of mutation?
gene mutation, chromosome mutation
give 2 examples of gene mutation .Describe how the mutation caused the disease and state the effect of the disease
1st example:Sickle cell Anaemia
How the mutation caused the disease:
1.A mutation occured in the gene controlling the production of haemoglobin protein
2.This caused the sequence of nucleotides in the gene to change,
3.Causing a different amino acid to be produced
4.The change in amino acid led to a change in the polypeptide and hence,the haemoglobin protein produced
effect of disease:
.instead of the normal haemoglobin,mutated haemoglobin is produced instead
.Mutated haemoglobin has an abnormal shape,causing the red blood cell to clump together to become sickle-shaped
.This reduces the ability of the red blood cells to transport oxygen which can lead to fatigue.It could also get stuck in narrow blood vessels which leads to death
2nd example:Albinism
How the mutation caused the disease:Albinism is an example of recessive gene mutation,where it is only expressed in homozygous recessive condition
effect of disease:Albinism is characterised by the absence of pigments in skin,hair and eyes
give an example of chromosome mutation, describe how the mutation caused the disease,and state the effect of the disease
example:down’s syndrome
How the mutation caused the disease:A mutation occured causing there to be an extra copy of chromosome 21
effect of disease:Abnormal physical and mental developments
describe discontinuous variation in simple terms
Traits that have only two clear-cut phenotypes(blood group is an exception)
describe continuous variation
traits that show more than two phenotypes
describe the differences between continuous variation and discontinuous variation in terms of genes
for continuous variation:
-usually controlled by many genes
-phenotype expressed is caused by the additive effect of many genes
for discontinuous variation:
.usually controlled by one or a few genes only
.genes do not show additive effect
describe the difference between continuous variation and discontinuous variation in terms of environmental conditions
for continuous variation:greatly influenced by environmental conditions
for discontinuous variation:relatively unaffected by environmental conditions
