Lecture 1 Flashcards
describe Human Variation
Variation may be discrete or continuous, but both are genetic in origin
give an example of and explain single gene human variation
Eye Colour is primarily determined by a single gene that has two possible alleles, brown (dominant) and blue (recessive).
Why can brown parents have blue children, but not vice versa?
chromosomes are in pairs, one from each ____.
____ are also in pairs.
genes controlling the same characteristics occupy identical positions on _______ chromosomes.
the gene pairs control one _______.
the genes of a corresponding pair are called _____.
alleles are _______ ____ of the same gene.
homologous chromosomes have the same ____ and carry the same gene ______.
chromosomes are in pairs, one from each parent/
genes are also in pairs.
genes controlling the same characteristics occupy identical positions on homologous chromosomes.
the gene pairs control one characteristic.
the genes of a corresponding pair are called alleles.
alleles are alternative forms of the same gene..
homologous chromosomes have the same length and carry the same gene sequences
describe inheritance of eye colour
brown is the dominant allele, blue is recessive
dominant allele expresses colour, so if baby is homozygous brown, or heterozygous it must have brown eyes, homozygous blue means it will have blue eyes
describe The Male-Determining Gene
Males have a Y chromosome which has the male determining gene “Sex Reversed on the Y (SRY)”
SRY switches on genes to force the gonads to develop in a male-like fashion and produce testosterone.
Testosterone travels around the blood stream, enters cells via Androgen receptors (AR) and switches on male genes.
how can a female have an X and Y
Androgen Insensitivity Syndrome Also known as Testicular Feminisation Syndrome X-linked recessive trait Gene encodes androgen receptor Mutant gene makes no functional receptor SRY gene makes functional SRY protein Gonads develop as testis Testis produce androgens Androgens have no effect
ow are genes passed on from parent to child?
Genes in the cell nucleus are physically located on 23 pairs of chromosomes
One set of 23 chromosomes is inherited from each parent
Therefore, of each pair of genes, one is inherited from a person’s mother, and one from their father
how are genetic disorders classified
Alterations in single genes
Variants in genes
Chromosomal imbalance
describe Single gene disorders
Some medical conditions are caused by a change in just one or both copies of a particular pair of genes. These are called “single gene disorders”.
The three common types of single gene disorders are called:
•Autosomal dominant
•Autosomal recessive
•X-linked
Dominant- These individuals are called Heterozygotes with one copy of the altered gene they are affected
Recessive-Homozygotes must have two copies of the altered gene to be affected
X-linked recessive- Males with an altered gene on the X- chromosome are always affected
give Examples of Autosomal Dominant Conditions
- Huntington disease
- Neurofibromatosis type 1
- Marfan syndrome
- Familial hypercholesterolemia
- Familial Adenomatous Polyposis (FAP)
- Prader-willi
describe marfan syndrome
a genetic disorder of the connective tissue • Heart, lungs and CNS problems • Very Tall • Eye Lens dislocation • Arachnodactyly (long fingers and toes)
give Examples of Autosomal recessive conditions
- Sickle Cell disease
- Cystic fibrosis
- Batten Disease
- Congenital deafness
- Phenylketonuria (PKU)
- Spinal muscular atrophy
- Recessive blindness
- Maple syrup urine disease
describe cystic fibrosis
The cystic fibrosis transmembrane conductance regulator (CFTR) gene controls the movement of salt and water in and out of your cells, so the lungs and digestive system become clogged with mucus, making it hard to breathe and digest food
describe sickle cell anaemia
- Caused by a defective allele for the synthesis of haemoglobin (HBB).
- Abnormal HBB is produced which can lead to sickle shaped red blood cells and blockage of capillaries.
- Bony infarctions in the phalanges and metacarpals leads to uneven finger length.
describe parents Autosomal recessive inheritance
Parent who are carriers for the same autosomal recessive condition have one copy of the usual form of the gene and one copy of an altered gene of the particular pair
A parent who is a carrier passes on either the usual gene or the altered gene into the eggs or sperm. The other parent who is also a carrier for the same condition passes on either the usual gene or the altered gene into
his/her eggs or sperm
describe x-linked inheritance
this is when a gene for a particular disease /trait lies on the x chromosome is x-linked
x linked genes are never passed from farther to son.
in affected family, affected females must have an affected family
males are homozygous for x-linked traits- they are never carriers. a single dose of mutant allele in men will produce a mutant phenotype regardless of wether it is dominant or recessive
Males are more likely to suffer from X-linked recessive disorders
describe how females are affected by X-linked recessive disorders
females carry 2 alleles of a gene. if one allele is defective the female is still normal as effect is masked y the normal allele
give Examples of X-Linked Recessive Conditions
• Fragile X syndrome • Haemophilia • Duchenne muscular dystrophy (DMD) (Becker BMD) • Fabry disease • Retinitis pigmentosa • Alport syndrome • Hunter syndrome • Ocular albinism • Adrenoleucodystrophy. 
describe haemophilia
- Severe bleeding
* Repeated bleeding around the joints leads to arthritis
describe X-linked recessive inheritance in males and females
One copy of an altered gene on the X chromosome causes the disease in a male.
An altered copy on one of the X chromosome pair causes carrier status in a female.
For a female to get an X-linked recessive disease then the father must also be affected.
disease is typically passed from an affected grandfather through carrier daughters to half of the grandsons. males are much more likely to be effected due to male hemizygosity (no backup copy of the gene on the second X chromosome)
females are mosaics for mutant and normal X chromosomes and normally show an intermediate phenotype which is clinically unaffected or very mildly affected bit biochemically abnormal. females can be severely affected when there is heavily skewed X-inactivation inactivating the majority of the normal x chromosomes
describe how x-linked dominant diseases or traits are passed on
all daughters of an affected male and normal female are affected as one X chromosome has to come from the farther
all sons of an affected male and normal female are unaffected as the Y comes from the farther
50% of children from an affected female and unaffected male will be affected
in the general population females are more likely to be affected than males as they have 2 X chromosomes, either of which could carry the mutant allele
give examples of 2 X-linked dominant disorders which are so severe male survival is rare
incontinentia pigment - majority of males spontaneously abort after first trimester, live born males are generally XXY or have somatic mosaicism
retts syndrome - males who inherit the MECP2 mutation suffer severe neonatal encephalothopy or if they survive will have severe mental retardation syndrome
describe polygenic inheritance
Single gene disorders are quite rare
Single gene disorders either give risk to a condition or they don’t
Most traits are Polygenic’ i.e. 1 trait coded by a number of altered and unaltered genes working together
what are some Common Polygenic Disorders
Alzheimer’s
Diabetes
Cancer
Eczema
describe Multifactorial inheritance and give congenital malformations and adult onset disorders
Inheritance controlled by many genes plus the effects of the environment
Congenital malformations
- Cleft lip/palate
- Congenital hip dislocation
- Congenital heart defects
- Neural tube defects Pyloric stenosis
- Talipes
Adult onset disorders
- Diabetes mellitus
- Epilepsy
- Glaucoma
- Hypertension
- Ischaemic heart disease
- Manic depression
- Schizophrenia
