Genotype, phenotype, inheritance part 1

Question 1

What is a phenotype?

Answer 1

Observable characteristics of an individual resulting from the interaction of its genotype with the environment

Question 2

How is a genotype presented as a phenotype?

Answer 2

Genes on chromosomes in the nucleus are translated to proteins in the cytoplasm which give rise to a phenotype

Question 3

What is the genotype?

Answer 3

Genetic makeup - sum total of genes carried within an organism

Question 4

What does the phenotype rise from?

Answer 4

Interaction of its genotype with the enivronment

Question 5

What environmental factors can alter the phenotype?

Answer 5

Environmental: radiation, lifestyle (e.g. activity, diet), mutagens, chemicals
Can also include diseases: heart disease, infection, cancer, cystic fibrosis, diabetes
Either interact with genotype to affect phenotype or alter phenotype directly

Question 6

How many genes does a human have?

Answer 6

Around 25,000

Question 7

How many alleles of a gene does a person have?

Answer 7

Two alleles of a gene

Question 8

What is an allele?

Answer 8

Alternative form of the same gene at the same position on a chromosome

Question 9

Homozygous

Answer 9

The two alleles of a gene are the same e.g. AA

Question 10

Heterozygous

Answer 10

The two alleles of a gene are different e.g. Aa

Question 11

What does hemizygous mean?

Answer 11

Only one allele of a gene (only the X chromosome- males are XY and one X chromosome in female is silent)

Question 12

Explain each inheritance pattern (2)

Answer 12

Dominant - dominant allele in heterozygosity determines the phenotype
Recessive - non dominant allele does not influence phenotype unless homozygous

Question 13

What is codominance?

Answer 13

Equal influence of two alleles on a phenotype- neither allele masks the expression of another

Question 14

Give an example of co-dominance

Answer 14

Human blood types
A and B blood groups are codominant

Question 15

What gene codes for the antigens on blood cells?

Answer 15

Isoglutamine

Question 16

State the 4 modes of inheritance

Answer 16

Autosomal (non sex chromosome)
Sex linkage (gene on X or Y)
Mitochondrial
Polygenic

Question 17

3 types of sex linked inheritance

Answer 17

X-linked recessive
X-linked dominant
Y-linked

Question 18

how are genetic traits usually studied in humans and why?

Answer 18

Usually by reconstructing a pedigree in families because it is ethically impossible to do experiment on humans by breeding them

Question 19

What shape and colour are affected and unaffected males and females in a pedigree tree?

Answer 19

Unaffected male - white square
Affected male - black square
Unaffected female - white circle
Affected female - black circle

Question 20

How is a carrier represented in a pedigree tree?

Answer 20

Square/ circle half black half white
Or a dot in the middle

Question 21

Representation of an unknown sex in a pedigree tree

Answer 21

Diomond

Question 22

What does III.17 mean (for example) on a pedigree tree?

Answer 22

Third Generation,
17 people across from left to right

Question 23

How are males and females affected by autosomal inheritance

Answer 23

Males and females equally affected - not sex-linked inheritance

Question 24

How are heterozygous and homozygous individuals affected by autosomal recessive inheritance?

Answer 24

Heterozygous will be unaffected
Homozygous will be shown in phenotype

Question 25

What is the chance of two heterozygous people having affected offspring in autosomal recessive inheritance?

Answer 25

25% chance of having affected offspring

Question 26

How does autosomal dominant affect heterozygous and homozygous?

Answer 26

Heterozygous - affected as only need one copy of gene
Homozygous - rarely found in this state as it is more lethal

Question 27

What is the chance of two heterozygous people having affected offspring in autosomal dominant inheritance?

Answer 27

50% change of having affected offspring

Question 28

Which autosomal inheritance skips and doesn’t skip a generation?

Answer 28

Recessive can skip generations
Autosomal dominant cannot skip a generation - affected individual in every generation

Question 29

What is the incidence of carriers in a population?

Answer 29

1 in 50

Question 30

In X-linked recessive inheritance, what daughters will affected males have?

Answer 30

Affected males will always have heterozygous daughter- one X from mother and one X from father so disease always passed to daughter

Question 31

In X-linked recessive inheritance, what parents would an affected female have?

Answer 31

An affected father and (at least) a carrier mother - recessive disease so need 2 copies of affected gene

Question 32

In X-linked recessive inheritance, what does the mother of an affected male have to be?

Answer 32

At least heterozygous carrier - Y is inherited from father so only one X gene needed from mother

Question 33

What are co-dominant alleles?

Answer 33

When neither allele in a heterozygous is dominant - both alleles are fully expressed, creating a new phenotype