inheritance [mendelian inheritance]

Question 1

what is inheritance

Answer 1

transmission of traits from one generation to another

Question 2

gene

Answer 2

a sequence of DNA nucleotide that controls the formation of a single polypeptide. it is also a unit of inheritance

Question 3

alleles

Answer 3

different forms of the same gene. they copy the same relative position on a pair of homologous chromosome

Question 4

homologous chromosomes

Answer 4

-contains alleles coding for the same gene found at the same gene loci

-has centromere at the same position and have the same lengths

Question 5

genotype

Answer 5

combination of alleles for a particular gene

Question 6

phenotype

Answer 6

expressed trait or outward appearance

Question 7

homozygous

Answer 7

two identical alleles of a particular gene

Question 8

codominance

Answer 8

both alleles express themselves in the heterozygote which has a phenotype intermediate between that of its pure bred parents

Question 9

autosomes

Answer 9

the other 22 pairs of chromosomes in humans that are not sex chromosomes

Question 10

variation

Answer 10

differences in traits between individuals of the same species

Question 11

discontinuous variation

Answer 11

-involves clear cut phenotypes that is controlled by one or a few genes with no intermediate forms between traits

-genes does not show additive effect

-traits are clearly distinguishable and are not affected by environmental conditions

-eg blood group, gender, single or double eyelid

Question 12

continuous variation

Answer 12

-involves a range of phenotypes that is controlled by many genes

-genes show additive effect

-affected by environmental conditions

-eg skin colour, height, shoe size

Question 13

additive effect [good to know]

Answer 13

multiple genes contribute cumulatively to a trait, resulting in a continuous range of possible outcomes [eg height, skin color]

Question 14

mutation

Answer 14

change in the sequence of a gene or in the chromosome number

Question 15

sickle cell anaemia

Answer 15

-caused by gene mutation

-a change in the sequence of nucleotide that codes for the production of an abnormal haemoglobin. haemoglobin S [HbS] is produced instead of haemoglobin A. this causes a change in the 3D shape of haemoglobin. HbS clumps together, making cell sickle shaped

Question 16

down syndrome

Answer 16

-caused by chromosome mutation

-extra chromosome in 21th pair
-copies of chromosome 21 did not separate during gamete formation

Question 17

mutagens

Answer 17

-agents that increase rate of spontaneous mutation
-e.g. ultraviolet light, and alpha, beta, and gamma radiations, tar

Question 18

what is natural selection

Answer 18

organisms with desirable genes and characteristics are ‘selected’ or ‘favoured’ to survive and pass on their genes to their offspring
-e.g. dark peppered moths

Question 19

describe natural selection

Answer 19

1. [spontaneous mutation definition, leading to mutation]
2. [variation, some with beneficial alleles, thus some is xx]
3. [selective advantage, selection pressure, natural selection]
4. [survive, pass down beneficial alleles]
5. [increase population]