W5 Intro to Genetic diseases Flashcards
What is the phenotype?
Individuals observable traits (height, eye colour)
Physical expression of genotype
What is the Genotype
The set of genes in our DNA which are responsible for a particular trait
What is meant by true breed?
The kind of breeding wherein the parents would produce offspring that would carry the SAME phenotype
e.g When the plants self-pollinate, all their offspring are of the same variety
What is meant by hybridisation?
What is a Monohybrid cross
-Mating, or crossing, of two varieties
-A cross between two parents that breed true for different versions of a single trait
Homozygous definition
2 identical alleles
Heterozygous
2 different alleles
Monohybrid inheritance F2 generation ratio:
9:3:3:1
What is the genome
What is an allele?
All the genes of an organism
Variations of a gene
PP or pp is a what pair of alleles?
Homozygous
What is a genetic disease?
Caused by an abnormality in an individual’s DNA. Most genetic disorders are quite rare
May/may not be inherited
How does a non-heritable genetic disorder occur?
Defects may be caused by somatic mutations - changes to the DNA of somatic cells after the birth
The defect can only be heritable if genetic disorder occurs in the germ line
What are the 4 types of genetic disorders?
- Single gene defects
- Chromosome abnormalities
- Multifactorial disorders
- Cancer
What is a gene?
Unit of heredity. Encodes the synthesis of a gene product. Usually a protein or RNA.
(small section of DNA)
What are the different mechanisms of inheritance? (3)
Autosomal dominant
Autosomal recessive
X-linked recessive or dominant
What is a Frameshift mutation?
insertion or deletion of one or more bases causing the alteration of the reading frame of the gene and a different set of codons, leading to an altered protein.
What type of disorder is sickle cell anaemia? (single gene defect)
Caused by what?
Autosomal recessive disorder
Caused by homozygosity (both alleles)- Point mutation in the beta-globin gene within chromosome 11
How are red blood cells affected for sickle cell anaemia?
Normal
Disease
Mendel- Pea experiment
F1 offspring?
F2 offspring?
100% yellow pea plants
75% yellow pea and 25% green pea (3:1)
Which allele dictates the organisms phenotype?
The dominant allele
Mendel’s third postulate:
Describe Independent segregation
During the formation of gametes, two copies (alleles) of each gene present in the parent separate so that each gamete receives only one allele for each trait
During fertilisation, a sperm cell carrying one or other allele fuses with an egg cell carrying one of the alleles to produce a zygote with two alleles
What is Albinism?
A disorder (recessive) that results in little or no production of the pigment melanin, (colour of the skin, hair and eyes)
How does a non-heritable genetic disorder occur?
Defects may be caused by somatic mutations - changes to the DNA of somatic cells after the birth
What is a single gene disorder?
A disease caused by changes or mutations that occur in the DNA sequence of a single gene
What is autosomal dominant?
If a single mutated allele is sufficient to cause the disease (heterozygosis)
What is autosomal recessive?
If both mutated allele must be inherited to be affected (homozygosis)
What is X-linked recessive or dominant?
mutated gene is present on the X chromosome
What is a Missense mutation?
These are base changes that alter the codon for an amino acid resulting in its replacement with a different amino acid.
What is a Nonsense mutation?
Base changes that convert an amino acid codon to a stop codon, resulting in a premature termination of translation and the production of a shortened protein.
What is a silent mutation?
Do not cause any change in an amino acid
What do Promoter mutations or mutations on other regulatory sequences do?
Affect the way gene transcription is regulated, often abnormally reducing or enhancing the expression of certain genes
What is the difference between a Normal RBC and a Sickle RBC?
Normal:
1.Red blood cells shaped like a disk
2.Haemoglobin (protein) carries oxygen to all parts of the body
Sickle:
1.Red blood cells form an abnormal crescent shape
2.Haemoglobin (protein) is abnormally shaped
3.Don’t move easily through your blood vessels
4.Form clumps and get stuck in the blood vessels
What is cystic fibrosis? (single gene defect)
How is it caused?
Autosomal recessive disease
-Mucus secretions accumulate in the lungs which block the airways, cause persistent infections and permanent lung damage
-Homozygosity (both alleles) for a point missense mutation in the CFTR gene within the chromosome 7
What is Huntington’s disease?(single gene defect)
autosomal dominant disease
-Heterozygosity (1 defective allele) in the huntingtin gene located on chromosome 4
-Neurodegenerative disease
What is Duchenne muscular dystrophy? (single gene defect)
- X-linked recessive disorder (DMD gene)
-Males suffer progressive weakening of the muscles - Males can’t be carriers
Chromosome abnormalities:
What are Numerical Abnormalities?
What are Structural Abnormalities?
- When an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy)
- When the chromosome’s structure is altered
