Inheritance

Question 1

gene

Answer 1

section of DNA that codes for a specific polypeptide

Question 2

genotype

Answer 2

genetic constitution of an organism. All the alleles an organism posesses.

Question 3

gene pool

Answer 3

all alleles within an interbreeding population at a specific time

Question 4

population

Answer 4

all individuals of the same species that occupy the same area/habitat at the same time

Question 5

phenotype

Answer 5

the expression of its genetic constitution and the interaction with the environment

Question 6

allele

Answer 6

different version of the same gene
- dom, codom or recessive
- alleles of same gene caused by mutation

Question 7

multiple alleles

Answer 7

more than 2 alleles for the same gene. hierarchy of dominance.

Question 8

locus

Answer 8

different alleles for the same gene are found at the same position on the homologous chromosome

Question 9

homozygous

Answer 9

if two copies of gene are the same allele, homozygous

Question 10

heterozygous

Answer 10

if two copies of a gene are different alleles

Question 11

dominant allele

Answer 11

always expressed in the phenotype

Question 12

recessive allele

Answer 12

only expressed in the phenotype if the genotype is homozygous

Question 13

codominant alleles

Answer 13

equally expressed within the phenotype

Question 14

diploid

Answer 14

somatic cells (ie: adult cells)
- two copies of a gene

Question 15

haploid

Answer 15

only have one copy of a gene
eg: gametes

Question 16

genetic crosses keys

Answer 16

“true-bred”/”pure-bred” = homozygous
P = parental generation
F1 = offspring of the generation
F2 = offspring of the F1 gen

Question 17

expected offspring phenotype ratios from hetero parents

Answer 17

mono = 3:1
codom = 1:2:1
dihybrid = 9: 3: 3:1
epistasis = 9: 4: 3/ 15: 1/ 9:7
autosomal linkage = 3:1 (no cross) 4:4:1:1 (recombinant alleles)

Question 18

dihybrid

Answer 18

two characteristics determined by genes found on different chromosomes

Question 19

epistasis

Answer 19

expression of one gene is influenced by another gene

Question 20

hardy weinberg equation

Answer 20

P + q =1
diploid: P^2 + 2Pq + q^2 = 1
ALWAYS find the recessive first
number divided by population size = q^2

Question 21

what does the hardy weinberg equation predict?

Answer 21

the allelic frequency of a gene from one generation to the next will be constant, if there is no:
- migration
- mutation
- selection for a particular allele
- a large population
- random fertilisation of gametes

Question 22

sex linked characteristics

Answer 22

• Y caries few non sex gene
• X carries sex gene and other body characteristics
• female needs two copies of a recessive allele for it to appear on phenotype, males only need 1
• mother- son inheritance, skip a gen
• if son affected, mother is not then not sex linked (if dominant allele)
• if daughter affected and father not, then not ressessive

Question 23

linkage groups

Answer 23

set of genes on same chromosome that tends to be inherited together

Question 24

state three causes of genetic variation

Answer 24

• mutation
• crossing over
• independent segregation
• random fusion of gametes

Question 25

how do multiple alleles of a gene arise?

Answer 25

mutation at different positions in the gene

Question 26

in genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. Suggest two reasons why.

Answer 26

- fertilisation of gametes is random - small sample size - epistasis - crossing over

Question 27

what is meant by a recessive allele?

Answer 27

only expressed when homozygous

Question 28

define gene linkage

Answer 28

genes/loci on same chromosome

Question 29

define epistasis

Answer 29

allele of one gene affects/masks the expression of another in the phenotype

Question 30

rules for dom alleles

Answer 30

- affected offspring must have one affected parent - unaffected parents = unaffected offspring - if both affected and unaffected offspring, then heterozygous

Question 31

rules for recessive alleles

Answer 31

unaffected offspring only hav e unaffected parents

Question 32

what is meant by the term phenotype

Answer 32

expression due to genetic constituion and interaction with the environment

Question 33

EXPLAIN HOW asingle base sub causes a change in the structure of a polypeptide

Answer 33

change in sequence of amino acids change in hydrogen/inic/disulfide bonds alters 3 structure