PATTERNS OF INHERITANCE

Question 1

Continuous variation

Answer 1

Individuals within a population vary within a range
Waist circumference
Fur length

Question 2

Discontinuous variation

Answer 2

Two or more distinct categories- each falls into only one of these categories and there are no intermediates
Blood group
Violet flower colour

Question 3

How is variation influenced by the environment

Answer 3

Sexual reproduction leads to variation in genotypes
The random fusion of gametes during fertilisation
Meiosis makes gamete with a unique assortment of alleles through crossing over and the independent assortment of chromosomes

Question 4

Polygenic characteristics

Answer 4

Inherited characteristics showing continuous variation and are usually influenced by many genes

Question 5

Monogenic characteristics

Answer 5

Inherited characteristics that show discontinuous variation and are usually influenced by only one gene

Question 6

Examples of variation that is influenced by the environment

Answer 6

Exoilation- plants grow abnormally long and spindly because they aren’t getting enough light
Chlorosis- plants don’t produce enough chlorophyll and turn yellow which is caused by a lack of magnesium in the soil

Question 7

How variation is influenced by genes and the environment

Answer 7

Usually shows continuous variation
Height of pea plants- pea plant come in fall and dwarf forms which is determined by genotype, however, the exact heights of the tall and dwarf plant varies because of environmental factors like light intensity and water availability
Body mass in animals- this is partly genetic but also influenced by environmental factors like diet

Question 8

Monogenic inheritance

Answer 8

The inheritance of a characteristic controlled by a single gene
3:1

Question 9

Codominance

Answer 9

Both alleles are expressed in the phenotype, neither one recessive
Sickle cell anaemia
1:2:1

Question 10

Multiple alleles

Answer 10

More than 2 alleles for the same gene

ABO blood group system- 3 alleles for blood type

Question 11

Dihybrid inheritance

Answer 11

Inheritance of 2 characteristics which are controlled by different genes
9:3:3:1

Question 12

Sex linkage

Answer 12

Genetic information for gender is carried on the 2 sex chromosomes
Males- XY
Females- XX
All males have 1 X chromosome so they only have 1 allele for sex linked genes, as they only have 1, thy express the characteristic even if it’s recessive
Colourblindness 
Haemophilia
Faulty alleles carried on X chromosome
2:1:1

Question 13

Autosomal linkage

Answer 13

Autosome- any chromosome that isn’t a sex chromosome
Genes on the same autosome are said to be linked, because they are on the same autosome they will stay together during the independent assortment stage of chromosomes in meiosis 1, their alleles will often be passed on to the offspring together
The closer the 2 genes on the autosome, the more closely they are linked and crossing over is less likely to split them up
If 2 genes are automatically linked, you won’t get the phenotypic ratio you expect in the offspring of a cross

Question 14

Epistatic genes

Answer 14

Many genes can control the same characteristic- they interact to form the phenotype
Epistasis- one gene masks the expression of the alleles of other genes
Baldness genes are epistatic to the widows peak genes
9:3:4