Genotype and Phenotype

Question 1

How does development start?

Answer 1

We begin life as just one cell at the time of fertilisation. This cell contains two sets of genes (one from mother and one from father). The genes are packaged into 46 protein parcels called chromosomes.

A single cell divides, and the genes are copied so that every cell possesses the full complement of genetic material. In the human body there are approximately 10 trillion cells!

Question 2

What are genes made out of?

Answer 2

Constructed of a chemical called DNA (about 2 metres). There are 300,000 genes across our DNA.

Question 3

How many chromosomes do we have?

Answer 3

23 pairs, the 23rd pair are sex chromosomes

Question 4

What are autosomes?

Answer 4

The first 22 pairs of autosomes, which are not sex chromosomes

Question 5

Genotype definition

Answer 5

• Genotype refers to the specific genetic make‐up of an individual, in the form of DNA
• The term was first used by Danish geneticist Wilhelm Johannsen (1857‐1927) to describe the entire genetic or hereditary constitution of an organism

Question 6

Types of chromosomal abnormalities

Answer 6

1. Deletion
2. Duplication
3. Inversion
4. Substitution
5. Translocation

Question 7

Deletion

Answer 7

A chromosome has less genetic information than normal

Question 8

Duplication

Answer 8

A chromosome has more genetic information than normal

Question 9

Inversion

Answer 9

The order of genetic information on a chromosome is changed

Question 10

Substitution

Answer 10

Information from one chromosome goes into another chromosome

Question 11

Translocation

Answer 11

Two different chromosomes swap their information

Question 12

Trisomies definition

Answer 12

The presence of a third copy of a chromosome

Question 13

Trisomies examples

Answer 13

Down syndrome and Kleinfelter syndrome

Question 14

Monosomies definition

Answer 14

The absence of one chromosome in the pair

Question 15

Monosomies example

Answer 15

Turner syndrome - only one X chromosome

Question 16

Cri du chat syndrome / 5Pminus syndrome

Answer 16

Missing chromosome 5, severe developmental delays with hyperactivity, aggression and repetitive movements. Found in 1 in 20k-50k newborns.

Question 17

Phenotype definition

Answer 17

The observable expression of characteristics and traits coded for by genes

Genotype + environment = phenotype

Phenotypic traits include obvious observable traits
* Physical phenotype – height, weight, etc…
* Cognitive phenotype – language, executive ability etc…
* Social phenotype – friendly, distant, outgoing etc…
Genotype and phenotype are NOT directly correlated

Question 18

Do genes effect phenotype?

Answer 18

Some genes only express a given phenotype in certain environmental conditions

Conversely, some phenotypes could be the result of multiple genotypes

Question 19

Karmiloff-Smith, Scerif, and Thomas (2002)

Answer 19

“heritability figures based on monozygotic twins for autism and dyslexia are 60% and 65%
respectively … suggesting that environmental factors play an important role”

Question 20

Differential susceptibility definition

Answer 20

Susceptibility to environment differs depending on genes involved in responsivity to the environment (plasticity genes)

Question 21

Epigenetic definition

Answer 21

The study of phenotype changes that do not involve changes to the DNA sequence (e.g. they affect gene activity or gene expression)

Question 22

Genomic method definition

Answer 22

Identify individuals with a known genetic disorder. Study those individuals to build up a phenotype / phenotypes associated with the disorder (eg behaviours / psychopathology)

Question 23

Phenomic method definition

Answer 23

Identify behavioural phenotypes. Explore possibly underlying genetic causes (eg the study of the prevalence/characteristics within families)

Question 24

Diagnosis definition

Answer 24

The identification of a disease, disorder, syndrome, condition etc.

Question 25

When does diagnosis happen?

Answer 25

• For most disorders diagnosis occurs after birth and may result from queries from parents, teachers, observable features / behaviours, medical problems
• Diagnosis may follow lengthy assessments of behaviours/ cognition/ the collection of information from parents / teachers etc.

Question 26

Prenatal diagnosis for Down syndrome name

Answer 26

Nuchal translucency scans

Question 27

When and how are the scans for Down syndrome completed?

Answer 27

• Performed routinely weeks 11‐13
• Assesses the collection of fluid under the skin at the back of a baby’s neck

Question 28

Amniocentesis - pre-natal test for down syndrome

Answer 28

• Under ultrasound guidance, a needle is inserted through the abdomen to remove a small amount of amniotic fluid.
• The cells from the fluid are then cultured and a karyotype analysis (an analysis of the chromosomal make‐up of the cells) is performed

Question 29

How is Williams Syndrome assessed (name and what happens)

Answer 29

A type of specialized chromosome analysis using fluorescent markers