Inheritance Flashcards
How would you describe DNA replication?
Semi-conservative: one strand of parent DNA conserved in daughter DNA catalysed by DNA polymerase
(DNA polymerase) (dNMP)n + dNTP -------------------------------> (dNMP)n+1 + PPi
Chain growth: 5’ —-> 3’
Reaction driven by pyrophosphate hydrolysis
What are the different stages of the cell cycle?
Interphase: (preparation for division)
G1 = cell content replication Cell cycle checkpoint S = DNA replication G2 = double-check & repair Cell cycle checkpoint
Mitosis (division)
note: G0 = temporary or permanent resting stage (no division)
What are the different stages of DNA replication in prokaryotes?
Circular naked chromosome
INITIATION:
Recognition of origin of replication
ELONGATION:
Moving replication forks
TERMINATION:
Two facing replication forks meet.
What are the different stages of eukaryotic DNA replication?
DNA pol extends leading strand continuously in 5’ -> 3’
Primase synthesises RNA primers. DNA pol extends primers to form Okazaki fragments on lagging strands (discontinuous)
Helicase unzips double helix. Ligase joins Okazaki fragments together.
Two facing replication forks meet. Ligase joins final fragments.
Chromosome no. stays the same, but one replicated chromosome consists of two sister chromatids.
What are the different stages of mitosis?
PROPHASE: chromosomes condense, mitotic spindle begins to form, two centrioles begin to form
PROMETAPHASE: nuclear membrane has disintegrated, chromosome centromeres attached to microtubules of spindle
METAPHASE: chromosomes aligned along equatorial plate
ANAPHASE: centromes of chromosomes divide and two daughter chromatids separate
TELOPHASE: complete separation of chromatids and two new nuclear membranes form
CYTOKINESIS: separation of daughter cells
What are the characteristics of mitosis? In what parts of the body does mitosis happen?
Somatic cell division
2 identical daughter cells produced
Continuous growth in epidermis, mucosae, bone marrow, & spermatogenesis
No recombination or random assortment.
One round of division
What are the different stages of meiosis?
MEIOSIS I:
PROPHASE: chromosomes condense, homologous chromosomes align and form bivalents
METAPHASE: nuclear membrane has disappeared, chromosomes aligned at equatorial plate, spindle attaches to centromeres
ANAPHASE: chromosomes separate to opposite poles of cell
TELOPHASE: nuclear membranes reform
CYTOKINESIS: cleavage into two daughter cells
MEIOSIS II:
Same as mitosis
What are the characteristics of meiosis?
4 non-identical daughter cells produced (gametes only)
Genetic variation produced by random assortment and crossing over (chiasmata formation)
Two rounds of division.
Outline the process of spermatogenesis.
Cell division to produce male gametes (~42 days)
Spermatogonium (2n) —–> Primary spermatocyte (2n) ————-> 4 x Spermatids(n) ————–> 4 x mature sperm (n)
Outline the process of oogenesis.
Cell division to produce female gametes (12-50years)
Oogonium (2n) —–> Primary Oocyte (2n) ——-> 1 x Ovum (n) + 3 x Polar bodies (lost) ————> Mature ovum (n)
Meiosis II stalled until puberty, only occurs when fertilised
What are the consequences of incomplete crossing over? What are the consequences of missegregation?
No crossing over ———–> trisomies, monosomies, empty gametes
Missegregation ————-> miscarriages, infertility, mental retardation
What is the definition of genotype and phenotype? How can each be affected by the environment?
GENOTYPE:
genetic makeup of an individual
affected by mutation e.g. UV
PHENOTYPE:
all observable characteristics of an individual as a result of the interaction between genotype and the environment
affected by lifestyle
How can genetic variation occur?
Mutation
Meiosis: independent, random assortment of chromosomes Crossing over (recombination of alleles)
What are the definitions of homozygous, heterozygous, and hemizygous?
HOMOZYGOUS: two alleles of the gene are the same (AA or aa)
HETEROZYGOUS: two alleles of the gene are different (Aa)
HEMIZYGOUS: only one allele of gene present (on X chromosome in XY individuals)
What is the definition of dominant and recessive alleles? What is the difference between autosomal and sex-linked disorders?
DOMINANT: allele in a heterozygote determines the phenotype
RECESSIVE: non-dominant allele in a heterozygote
AUTOSOMAL: on non sex-linked chromosomes
SEX-LINKED: X & Y
What are the characteristics of autosomal dominant disorders/pedigrees?
Heterozygotes affected.
Males and females equally affected
Disease rarely found in homozygous form (AA = lethal)
Every affected individuals has a 50% chance of having affected offspring
Disease cannot skip a generation
Example: Huntington’s disease
What are the characteristics of autosomal recessive disorders and pedigrees?
Heterozygotes unaffected (Aa)
Males & females equally affected
Two carriers have a 25% chance of having affected offspring
Skips generations
e.g. cystic fibrosis
What are the characteristics of X-linked recessive disorders and pedigrees?
Hemizygous males and homozygous females affected (therefore, disease more common in males)
Heterozygous female carrier has 50% chance of having affected sons
Affected males cannot give traits to sons (mother passes X chromosome to sons)
Affected males will have a heterozygous carrier mother
Affected females will have a heterozygous carrier mother and an affected father
e.g. Haemophilia A
What is the definition of codominance? Give an example.
Both alleles of a gene are fully expressed (phenotype is neither dominant or recessive)
e.g. human ABO blood type
alleles Ia & Ib = blood type AB
What is the definition of complementation? Give an example.
Two mutant alleles on two different genes on different chromosomes affect the same phenotype, so the wild type phenotype results despite the mutant alleles.
e.g. albinism: two albino parents with different mutated genes have children with normal pigmentation
What is the definition of linkage? What are the important characteristics of linked genes?
Genes are linked when they are close together on the same chromosome, hence they tend to be inherited together and do not show independent assortment at meiosis.
Therefore parental alleles > recombinant alleles
What is the definition of recombination? How do calculate the recombination frequency? What does the recombination frequency depend on?
Exchange of genes between chromosomes, resulting in a different combination of alleles in the offspring than in the parental alleles.
No. of recombinants/No. of recombinants + Parentals being considered x 100
R.F. of linked genes depends on distance between the genes
