UNIT 3.4 Flashcards
(28 cards)
Mendels Law
Which Laws:
Mendelian Ratios:
Father of genetics → performed experiments on a variety of different pea plants → discovered principles of inheritance
Law of segregation: Genes come in pairs and are inherited as distinct units, one from each parent
Principle of dominance: recessive alleles will be masked by dominant alleles
Non-mendelian ratios:
*Co-dominance of specific alleles eg: pink flowers from red and white ones
*Sex-linked effects eg: color blindness
*Environmental influence on inheritance
Haploid Cells
Gametes are haploid and contain one copy of each chromosome, therefore one allele of each gene
Formed by the process of meiosis – males produce sperm and females produce ova
The two alleles of each gene separate into different haploid daughter nuclei during meiosis
As homologous chromosomes carry the same genes, segregation of the chromosomes also separates the allele pairs
Fusion of Gametes
When male and female gametes fuse during fertilization → form a zygote (diploid) containing two alleles for each gene (can be the same or different alleles)
For any given gene, the combination of alleles can be categorized as follows
If the maternal and paternal alleles are the same, the offspring is said to be homozygous for that gene
If the maternal and paternal alleles are different, the offspring is said to be heterozygous for that gene
Exception: Males have only one allele for each gene located on a sex chromosome, as these chromosomes aren’t paired (XY)
Models of Inheritance
Phenotype
Genotype
Proteome (total number of proteins) is larger than genotype
Genotype
*Allele combination: homozygous or heterozygous
Eg: bb or BB or Bb
Phenotype
*Physical expression: determined by both the genotype and environmental influences
Eg: green eyes, brown eyes
Dominant Allele
Dominant allele – Allele that is expressed in the heterozygous genotype
Heterozygous state: if present it will mask the recessive allele
Eg: BB or Bb → brown eyes
Recessive Allele
Recessive allele – Allele that is not expressed in a heterozygous genotype
Only being present in a homozygous state of two recessive
Eg: bb → blue eyes
CO-Dominance (punnet square)
*Check Good Notes for Diagrams
Co-dominant alleles – Pairs of alleles which are both expressed equally in the phenotype of a heterozygous individual (they have a joint effect)
Flower Petals:
Parent Genotypes: CRCW x CRCW
Parent Phenotype: Pink x Pink
Offspring Genotype Ratio: 1:2:1 (CRR:CRw: CWW)
Offspring Phenotype Ratio: 1:2:1 (Red: Pink: White)
Inheritance of ABO Blood Groups - Multiple Alleles
A B
O
Blood Transfusions
Glycoproteins
Controlled by a single gene with multiple alleles (A,B,O)
*A and B alleles are codominant and each modifies the structure of the antigen to produce different variants
*O allele is recessive and does not modify the basic antigen structure
As humans produce antibodies against foreign antigens, blood transfusions are not compatible between certain blood groups
Consequences: agglutination (clumping) –> haemolysis
The glycoproteins (found in the cell membrane are the markers or sensors)
Inheritance of ABO Blood Groups - Multiple Alleles (AB)
Can receive: any other type
Because: they already possess both antigenic variants on their cells)
(iA iB)
Inheritance of ABO Blood Groups - Multiple Alleles (A)
Cannot receive: B blood of AB blood
Because: the isoantigen produced by the B allele is foreign
(iAiA or iAi)
Inheritance of ABO Blood Groups - Multiple Alleles (B)
Cannot receive: A blood or AB blood
Because: as the isoantigen produced by the A apple is foreign
(iBiB or iBi)
Comparison of Predicted and Actual Outcomes of Genetic Crosses
The genotypic and phenotypic ratios calculated via Punnett grids are only probabilities and may not always reflect actual trends
When comparing predicted outcomes to actual data, larger data sets are more likely to yield positive correlations
Inheritance of ABO Blood GRoups - Multiple Alleles (O)
Can receive: only from O blood
Can donate: Universal
Because: both antigenic (A and B) variants are foreign
(ii)
Gene Diseases
Somatic Mutations
Germline Mutations
Genetic diseases are caused when mutations to a gene (or genes) abrogate normal cellular function → development of a disease phenotype
Somatic mutations → occur in non-germline tissues → cannot be inherited → eg: breast tumour
Germline mutations → present in egg or sperm → can be inherited
Sickle Cell Anaemia - Codominant
Allele Nature
Combinations
Location of Mutation
Sex Linked
Symptoms
A codominant genetic disease only requires one copy of the faulty allele to occur (eg: sickle cell anaemia)
Heterozygous individuals will have milder symptoms due to the moderating influence of a normal allee
Allele Nature: Co-Dominant
Combinations:
HbA → Normal Haemoglobin
HbS → Allele for sickle Hemoglobin
HbAHbA → Homozygous HbA → Normal
HbAHbS → Heterozygous → Carrier → Malaria protection
HbSHbS→ Homozygous HbS → Sickle Cell Disease → Malaria protection
Location of Mutation:
HBB genes on chromosome 11
GAG mutated into GTG
Sex Linked: NO
Symptoms: Clots in blood vessels (capillaries because of their abnormal shape
Immune to malaria
Cystic Fibrosis - Autosomal Recessive
Allele Nature
Combinations
Location of Mutation
Sex Linked
Symptoms
*Check Good Notes for Diagrams
An autosomal recessive genetic disease will only occur if both alleles are faulty (eg: cystic fibrosis)
Carrier: the heterozygous individual will possess one copy of the faulty allele but not develop disease symptoms
Allele Nature: Autosomal Recessive
Combinations:
CC → Normal
Cc → Normal carrier
cc → cystic fibrosis
Location of Mutation: CFTR gene on chromosome 7
Sex Linked: No
Symptoms: Causes secretion of mucus to become very thick. The thick mucus blocked the airway tubes, especially in the lungs.
Phenylketonuria (PKU)
Allele Nature
Combinations
Location of Mutation
Sex Linked
Symptoms
Allele Nature: Autosomal Recessive
Combinations:
TT → normal
Tt → carrier
tt → PKU
Location of Mutation: (PAH), found on chromosome 12
Sex Linked: No
Symptoms:
Mutation due to base substitution where there is a change in a single base results in a different amino acid
- tyrosine
- hydroxylase
phenylalanine cannot be converted to tyrosine in the body, making it to build up
- Developmental problems
- Seizures
Huntington’s Disease
Allele Nature
Combinations
Location of Mutation
Sex Linked
Symptoms
*Check Good Notes for Diagrams
An autosomal dominant genetic disease requires one copy of a faulty allele to cause the disorder (eg: Huntington’s disease)
Homozygous dominant and heterozygous individuals will both develop a full range of disease symptoms
Allele Nature: Dominant
Combinations:
Hh → Huntington’s disease
hh → normal
Location of Mutation: HTT gene on chromosome 4
Sex Linked: No
Symptoms: Neuron degeneration will lead to brain disorder, affecting the ability to think, talk and move
Sex Linked Diseases
*Check Good Notes for Diagrams
Due to mutations in the base substitutions
When a gene controlling a characteristic is located on sex chromosomes (X or Y)
*The Y chromosome is much shorter than the X chromosome and contains only a few genes
*The X chromosome is longer and contains many genes not present on the Y chromosome
Sex-linked conditions are usually Y-linked
*They are more common in males as there is only one X chromosome, so any allele present in the non-homologous part of the X chromosome will be expressed
*Females have 2 X chromosomes → 2 alleles → X-linked dominant traits are more common in females
*Human males have only 1 X chromosome → 1 allele → X-linked recessive traits are more common → they cannot be masked by a second allele → sex-linked disease is more common in men
Only females can be carriers
Red Green ColorBlindness
Allele Nature
Combinations
Location of Mutation
Sex Linked
Symptoms
Allele Nature: Recessive
Combinations:
XA → unaffected (normal vision)
Xa → affected (color blindness)
Location of Mutation: Mutation to the red or green retinal photoreceptors
X chromosome
Sex Linked: Yes
Symptoms: Failure to distinguish between red and blue. Loss of certain frequencies of light
Hemophilia
Allele Nature
Combinations
Location of Mutation
Sex Linked
Symptoms
Allele Nature: Recessive
Combinations:
XH → unaffected (normal blood clotting)
Xh → hemophilia
Location of Mutation: X chromosome
Sex Linked: Yes
Symptoms:
Clotting response to injury does not work
The patient may bleed to death
Pedigree Chart
Sex Linked, Recessive
Autosomal, Recessive
Autosomal, Dominan
*Check Good Notes for Diagrams
Males → squares
Women → circles
Shaded symbols → individual affected by a condition
Unshaded symbols → individual not affected
*Sex Linked, Recessive
- Affects only one gender (males are predominantly affected)
- It is able to skip generations
*Autosomal, Recessive:
- Affects males and females
- Less population with disease than with disease
*Autosomal, dominant
- Affects women and male
- More people with disease than without the disease
- Present in all generations
Radiation and Causes of Mutation: Mutagens
Mutagens: Mutagens are agents that cause or increase the frequency of mutations by altering the genetic material of an organism.
They include various types of radiation and chemicals.
Exposure to mutagens can result in the formation of new alleles, some of which may be harmful and contribute to the development of genetic diseases or cancer.
Radiation and Causes of Mutation: Chemical Mutagens
Chemical Mutagens: Chemical mutagens are substances that can trigger changes in an organism’s genetic material.
Examples are workplace chemicals, cigarette smoke, and specific additives like nitrites present in cured meats.
These chemicals can increase the mutation rate and contribute to the development of genetic diseases and cancer.
