6.1.2 Patterns Of Inheritance

Question 1

What are the two types of variation and give an example?

Answer 1

Continuous/ Quantitative - measurable, when individuals in a population vary within a range - there are no distinct categories e.g. height, waist length or fur length
Discontinuous/ Qualitative - not measurable, when there are two or more distinct categories - each individual falls into only 1 of these categories, there are no intermediates e.g. blood group and tongue-rolling ability

Question 2

Define Phenotype

Answer 2

The physical expression of genotype

Question 3

Define Genotype

Answer 3

The alleles an organism has

Question 4

Define Allele

Answer 4

Form of an allele

Question 5

Define Polygenic and give an example

Answer 5

Inherited characteristics that show continuous variation - influenced by many genes
E.g. Human skin colour is polygenic - comes in a lot of different shades of colour

Question 6

Define Monogenic and give an example

Answer 6

Inherited characteristics that show discontinuous variation - usually only influenced by one gene ( or a small number of genes)
E.g. violet flower colour (either coloured or white) is controlled by only 1 gene

Question 7

What 3 factors impact phenotypic variation?

Answer 7

1. Genotype
2. The Environment
3. Genotype and the environment

Question 8

How does the environment impact phenotypic variation and give 2 examples?

Answer 8

Factors such as climate, food and lifestyle. Characteristics controlled by environmental factors can change over an organism’s life

1. Etiolation - when plants grow abnormally long and spindly because they’re not getting enough light
2. Chlorosis - when plants don’t produce enough chlorophyll + turn yellow - caused by several environmental factors e.g. lack of magnesium in the soil

Question 9

How do the environment and genotype, both influence phenotypic variation.

Answer 9

Genotype tends to influence the characteristics an organism is born with but environmental factors can influence how some of those characteristics develop
E.g. Body mass in animals, partly genetic but strongly influenced by environmental factors such as diet
Also Height of pea plants - whether they are dwarf or tall is determined by genotype but the exact height of the tall and dwarf plants varies because of environmental factors e.g. light intensity and water availability

Question 10

Define a gene

Answer 10

A sequence of bases on DNA molecules that codes for a protein (polypeptide) which results in a characteristic

Question 11

Define an Allele

Answer 11

Different versions of the same gene

Question 12

Define Locus

Answer 12

Allele of each gene on a fixed position

Question 13

Are phenotypes always visible characteristics?

Answer 13

No, as metabolic rate is a phenotype but is not directly visible

Question 14

Define homozygous and heterozygous?

Answer 14

Homozygous - carries 2 copies of the same allele

Heterozygous - carries 2 different alleles

Question 15

Define dominant allele

Answer 15

An allele that is always expressed

Question 16

Define Recessive allele

Answer 16

Alleles which are only expressed when 2 are present

Question 17

Define Codominant alleles

Answer 17

When both alleles are expressed in phenotype as neither one is recessive

Question 18

Define a carrier

Answer 18

A person carrying an allele which is not expressed in the phenotype but can be passed onto offspring.

Question 19

Define Monogenic/Monohybrid inheritance

Answer 19

Inheritance of a characteristic controlled by a single gene

Question 20

What is the first set of offspring called?

Answer 20

F1 generation

Question 21

What is second set of offspring called?

Answer 21

F2 generation

Question 22

What is a dihybrid cross?

Answer 22

When 2 genes are simultaneously inherited, inheritance of 2 characteristics, which are controlled by different genes - each of the 2 genes have different alleles

Question 23

Define Heterogametic

Answer 23

They have 2 types of sex chromosomes (X AND Y)

Question 24

Define Homogametic

Answer 24

Only have one kind of sex chromosome (X AND X)

Question 25

Define sex linkage

Answer 25

Alleles that code for these characteristics are located on the sex chromosome

Question 26

Why does is the Y chromosome less likely to carry genes?

Answer 26

They are smaller than X chromosomes and thus carry less genes so most genes on sex chromosomes are carries by X chromosome (X linked genes)

Question 27

Why are males more likely to carry sex-linked related diseases (express sex-linked genes)?

Answer 27

As they only have one X chromosome, they often only have one allele for sex-linked gene as as they only have one copy they express the characteristic even if it is recessive

Question 28

Define Autosome

Answer 28

Any chromosome that isn’t a sex chromosome

Question 29

What is linkage on autosomal genes

Answer 29

The genes on the same autosome that stay together during IA and M1 and so their alleles will be passed onto offspring together

Question 30

What can stop autosomal genes?

Answer 30

Crossing over - the closer the genes are on the autosome the less likely crossing over will split them apart.

Question 31

How does autosomal linkage impact phenotypic ratios + give an example.

Answer 31

You won’t get the expected phenotypic ratio of offspring of a cross
E.g. an expected ration of 9:3:3:1 of a dihybrid cross of two heterozygous parents will actually result in a 3:1 ratio as the autosomally - linked alleles are inherited together, meaning more offspring will get heterozygous genotype

Question 32

What is a back cross?

Answer 32

Crossing the offspring with one of the parents

Question 33

What is Epistasis and give 2 examples?

Answer 33

When the allele of one genes blocks/masks the expression of the alleles of another gene
E.g. Widow’s peak - if one has alleles that code for baldness, it does not matter if person has allele for widow’s peak as you have no hair - the baldness genes are epistatic to the widow’s peak gene
E.g. Flower pigment is controlled by 2 genes, if gene 1 codes for yellow + gene 2 odes for enzyme that turns yellow pigment orange. If one doesn’t have the Y allele it won’t matter if you have R allele or not as flower will be colourless