ineritence patterns Flashcards
dominant def
an allele always expressed in the phenotype regardless of copy number
recessive def
an allele that is only expressed if present on both chromosome homologs
homozygous def
Homozygous – both homologs have the same allele at a given locus
heterozygous def
Heterozygous – the allele at a given locus differs between homologs
co dominant def
Co-dominant – two alleles that are both expressed in the heterozygote
Mendelian Inheritance
every individual has two copies (allele) of each gene
and each allele segregates into a copy of inheritance material in a gamete
alleles reunite randomly at fertilisation
trait
Trait – a genetically determined characteristic; similar to a phenotype
carrier
a heterozygote with one recessive allele at a given locus; usually refers to a disease allele
mono hybrid cross
mating between two individuals that differ in only one trait
dihybrid cross
mating between two individuals that differ in two traits
linkage
occurs between two genes that are located near each other on a chromosome
why does independent assortment occur?
because if crossing over and recombination
why is crossing over and recombination done
- separate alleles into different gametes
- Alleles previously linked to the same chromosome are inherited independently
how does chromosomes become recombinant
Homologous chromosomes pair during meiosis (prophase I) and form chiasmata
Breakages at chiasmata allow sections of DNA to be swapped between homologs
Chromosomes become recombinant
mendelian inheritance - dominance
observed all meme era of the f1 gen had the same phenotype
- indentical to one of the pure bred parents
When he crossed individuals from F1, the other pure-bred phenotype reappeared with a frequency of 25% in F2 gen
can also be effected by the environment
THE RATIO OCCURS EVERYTIME PARENTS MATE NOT DEPENDANT ON NUMBER OF OFFSPRING
what did the reappearance of missing phenotype prove - mendelian’s dominance
Blending of parental units of heredity
Each individual has two copies of a gene
what did mendel conclude
that one trait is dominant over the other and hybrids are therefore ‘unstable’
pedigree
chart that shows inheritance of a trait / disorder through family generations
what’s a proband - pedigree
first person in a tree to be diagnosed with the condition
what’s a proband - pedigree
first person in a tree to be diagnosed with the condition
autosomal dominant
if an effected parent mates with an unaffected parent, there is a 50% chance that the disease will be inherited
characteristics of autosomal dominant inheritance
polydactyly
autosomal dominant disorder
has extra digit (s)
caused by dominant allele
autosomal recessive diseases
rare - but more common than dominant
must be inherited from both parents
heterozygous carriers - but will not express it phenotypically
generation skip can occur
consanguinity is common in family trees
cystic fibrosis
autosomal recessive disorder
must be inherited from both parents
causes severe damage to the lungs, digestive system and other organs in the body
reduced penetrance
when individuals with disease genotype do not always express disease phenotype
norm happens in disorders with autosomal dominant inheritance pattern
retinoblastoma
malignant eye tumour
autosomal dom disease
obligate carries have affected parent and child
what’s a penetrance rate
% of obligate carriers that express disease
de novo mutation
proband causes de novo
likely cause of disease if parents and grandparents are unaffected
recurrence risk for siblings is not elevated
Recurrence risk for offspring is elevated
Most autosomal dominant diseases arise from de novo mutation
7/8 achondroplasia sufferers
Expression of disease phenotype reduces likelihood of reproduction
de novo germline mosaicism
Germline mosaicism may account for multiple siblings in a family without a history of a disease
Mutation occurs in parental germline
Few if any somatic cells are affected
Recurrence risk to siblings is the same as if the parent were affected
Occurs in 20% of haemophilia A cases
de novo germline mosaicism
Germline mosaicism may account for multiple siblings in a family without a history of a disease
Mutation occurs in parental germline
Few if any somatic cells are affected
Recurrence risk to siblings is the same as if the parent were affected
Occurs in 20% of haemophilia A cases
structure of mitochondria
Mitochondria have a double membrane which controls transfer of metabolites:
Outer membrane is smooth
Inner membrane is highly folded into cristae which are covered in stalked particles
Presence of two membranes creates two internal compartments:
Intermembrane space plays an important role in the proton pump
Matrix contains *DNA, ribosomes and enzymes
mitochondria- cytoplasmic inheritance
Mitochondrial inheritance is extranuclear and maternal
Mitochondria divide by binary fission*
Average human sperm contains 50-75 mitochondria
Average human egg contains 100,000 – 600,000 mitochondria
In the zygote, male mitochondria are diluted by the female
mtDNA is used extensively in evolutionary biology and ancestry studies
what’s the function of mitochondria
site of atp synthesis
why do mitochondria have their own genome
many proteins needed in the etc
what are nucleoids
highly condensed and circular structures that store mtDNA
how many genes do mtDNA have
37genes
13 involved in oxidative phosphorylation
22 are tRNA genes
2 are rRNA genes for each ribosome subunit**
maternal inheritance - mitochondria
males can inherit but not transmit
females can transmit to both genders
mitochondrial inheritance disease
mtDNA has a very high mutation rate
10x higher than nDNA
Oxidative phosphorylation creates free radicals that act as mutagens
Most mtDNA mutations are lethal because of ATP demands during embryogenesis
If viable carriers of the mutation are likely to suffer from neurodegeneration
Neurones consume 20% of all ATP
no cure
can chase deafness blindness diabetes heart/liver failure
