Week 2 : Biological Foundations Flashcards
What is a phenotype ?
A phenotype is a directly observable characteristic
* Natural hair colour
* Certain types of diseases
* Facial dimples
* Skin pigmentation
* Eye colour
What is a genotype?
An individual’s genetic makeup
Genes
Hereditary information made up of DNA
and transmitted from parent to child at conception.
e.g. portion of DNA that codes for a trait
NOTE = bases in this segment determines the protein that is built
DNA
Deoxyribonucleic acid
The double helix molecule whose chemical code makes up chromosomes and serves as our genetic endowment
Chromosomes
Chromosomes: Rod-like structures in the cell nucleus
that store and transmit genetic information
23 pairs for total for 46
order from biggest to smallest
DNA, Chromosomes, Genes
Chromosomes -> DNA -> genes
Mitosis
The process of cell duplication, in which each new cell receives an exact copy of the original chromosomes.
Meiosis
The process of cell
division that halves the number
of chromosomes and leads to
gamete (sperm/ egg) formation
Zygote
A newly fertilised cell formed by the
union of sperm and ovum at conception (has the normal number of chromosomes as half comes from sperm/ dad and half from egg/ mum).
-> will go through mitosis self division from this point forward
Autosomes
The 22 pairs of
chromosomes that are
not sex chromosomes
Sex Chromosomes
23rd pair of chromosomes
* Determines sex
* XX = female
* XY = male
Identical/ Monozygotic Twins
- Occur when a zygote separates into
two clusters of cells. - Have the same genetic make-up.
- Occur in about 1 in every 330 births.
Fraternal/Dizygotic Twins
- No more genetically alike than
ordinary siblings. - Occur following the release and
fertilisation of two ova (i.e. two eggs are fertilized by 2 sperm) - The most common type of multiple
birth.
-Increasing in frequency because of the use of IVF
Alleles
Different forms of the same gene
e.g. eye colour = trait, which colour you have =alleles
▪ Alleles are found at the same place on each chromosome in the pair.
▪ One allele is inherited from each parent.
Homozygous
Having two identical alleles at the
same place on a pair of chromosomes.
▪ The inherited trait is displayed
Heterozygous
Having two different alleles at the same
place on a pair of chromosomes.
▪ The relationship between the alleles
determines the phenotype, or the observable
characteristic.
Dominant allele
If even one is inherited then the allele it codes for will be expressed
e.g. Non red hair is dominant (RR or Rr)
Recessive allele
Both recessive alleles need to be inherited to be expressed e.g. Red hair is recessive (rr)
This means both parents need to carry at least one recessive allele even if they themselve are dark head
X-Linked Inheritance
- A pattern of inheritance in which a recessive gene is
carried on the X chromosome, so that males are more likely than females to be affected
-This is because males only have one x chromosome so only need to inherit recessive allele once for it to be expressed , females need to inherit two
e.g. Hemophilia
Down Syndrome
*An autosome abnormality
- The most common chromosomal abnormality.
- Typically results from a failure of the twenty-first pair of chromosomes to separate during meiosis (extra genetic material)
- Causes delays in learning and development.
- Cannot be cured but problems can be eased
if people with Down Syndrome have the right
help and if other people have a positive
accepting attitude
Mosaic Down syndrome
Failure of separation of 21 chromosome pair happens later in meiosis process
Some cells have normal expression and some cells have the extra genetic material (chromosome) i.e. some with 46 and some with 47 chromosomes
very rare
When do sex chromosome disorders become present?
depends on the disorder, some might be present from birth while others might only be present from puberty
What are the most common examples of sex chromosome disorders?
-The presence of an extra chromosome (either X or Y), OR
-The absence of one X in females
What is XYY syndrome ? Incidence? Treatment?
-Extra Y chromosome
-Above average height, large teeth, sometimes severe acne
-Normal to mildly impaired intelligence
-Male sexual development and fertility are normal
-Incidence = 1 in 1,000 male births
-No special treatment necessary
What is XXX syndrome ? Incidence? Treatment?
-Extra X chromosome
-Tallness and impaired verbal intelligence
-Female sexual development and fertility are normal
-1 in 500 to 1250 female births
-Special education to treat verbal ability problems is needed
What is Klinefelter Syndrome ? Incidence? Treatment?
XXY
-Extra X chromosome
-Tallness, body fat distribution resembling that of females, incomplete development of sex characteristics at puberty, sterility and impaired verbal intelligence
-In in 900 male births
-Treatment = hormone therapy at puberty to stimulate development of sex characteristics, special education to treat verbal ability problems
What is Turner Syndrome? Incidence? Treatment?
-Missing X chromosome, XO
-Short stature, webbed neck, incomplete development of sex characteristics at puberty, sterility and impaired spatial intelligence
-1 in, 2500 to 8000 female births
-Hormone therapy in childhood to stimulate physical growth and at puberty to promote development of sex characteristics, special education to treat spatial ability problems
Epigenetic effects
The ways in which environmental
influences alter gene expression
Gene Expression
The activation of particular genes in
particular cells of the body at particular times
Epigenetics
The effect that ongoing, bi-directional exchanges between heredity
and all levels of the environment have on development.
- Genes affect children’s behaviour and experiences, but their
experiences and behaviour also affect gene expression. - Stimulation—both internal to the child (such as the release of
hormones into the bloodstream) and external (such as home and
school)—triggers gene activity.
