Genetics

Question 1

Alleles are

Homozygous

Heterozygous

Answer 1

2 genes at the same locus of homologous chromosomes

If identical

If different

Question 2

Genotype

Answer 2

Genetic make-up of Alan organism

Question 3

Phenotype

Answer 3

Observable characteristics of an organism - can go down to a biochem level

Question 4

Karyotypes

Answer 4

Method of studying chromosomes - make a chromosomal squash, photograph print and pair them

Can spot extra ones such as downs - trisomy 21

Can see sex chromosomes

Question 5

Sex linked inheritance

Answer 5

Inheritance of genes located on the x or Y chromosomes - as x is bigger most sex linked diseases are x linked e.g. Heamophilia

Question 6

Autosomal inheritance

Answer 6

Genes located on any of the other 22 chromosomes

Question 7

Mandels law of segregation

Answer 7

During gamete formation each member of an allelic pair segregates from the other member to form the genetic constitution of the gamete

Question 8

Mandela law of independent assortment

Answer 8

Separate genes for separate traits are passed independently of one another from parents to offspring

Question 9

Punnet squares

Answer 9

Diagram

Question 10

Dihybrid cross

Answer 10

Diagram

Question 11

Gene expression

Answer 11

DNA > (transcription}> mRNA > (translation}> proteins

Gene > control region and coding region

rRNA - ribosomal RNA
tRNA - transfer RNA carries aas in ribosomes to make proteins

Question 12

Incomplete dominance

Answer 12

One allele for a trait not completely dominant over the other
Results in a combined phenotype e.g. Sickle cell trait (vs sickle cell anaemia)

Question 13

Codominance

Answer 13

Both alleles independently express

E.g. ABO blood typing
I - recessive, Ia and Ib which are Codominance so proteins a and b are expressed

If antigen A is expressed so is anti-b antibodies and vice versa. If both antigens then no antibodies, if no antigens both antibodies

Question 14

Polyallelic series

Answer 14

Only 2 alleles can be present at 1 locus of a homologous pair of chromosomes but a series of alleles may be present in a population - gene pool

Question 15

Polymorphism

Answer 15

Various forms of an allele - formed by mutations to the genes - most favourable selected for ( Darwin)

Question 16

Lethal genes

Answer 16

Death of organism carrying it

Usually recessive and expressed only in homozygotes

E.g. Chlorophyll production in plants

Question 17

Epistasis

             Recessive

             Dominant

Answer 17

Effect of a gene is masked by one or more other genes located at different loci (vs dominance which is the interaction of genes at the SAME loci)

Recessive allele of one gene masks the effects of either allele of the second gene

Dominant allele of one gene masks the effects of either allele of the second gene

Question 18

Pleiotropy

Answer 18

Single gene influences multiple phenotypic traits

Therefore mutation will have an effect in some/all traits simultaneously

Question 19

Variable expressivity

Answer 19

Variability of the manifestation of a characteristic

Question 20

Reduced Penetrance

Answer 20

Proportion of people with a particular gene mutation who exhibit signs and symptoms of a genetic disorder

If some people with the mutation do not develop features of the disorder = reduced/incomplete Penetrance

Question 21

Polygenic inheritance

Answer 21

More than one gene controls one character