Chromosomes and Genes Flashcards
What is the defining feature of all evolving living organisms
The ability to reproduce
Karyotype
number and appearance of human chromosomes
For genes to be functional DNA must be able to (three things)
- replicate
- separate its 2 copies at mitosis
- maintain itself between generations
Chromosome Abnormalities
Monosomy
Missing Chromosomes
Chromosome Abnormalities
Trisomy
Extra Chromosomes
Down Syndrome
Trisomy 21
Turner Syndrome
45X
One X no Y or X
Klinefelter syndrome
47XXY
Extra X
Edwards Syndrome
Trisomy 18
Patau Syndrome
Trisomy 13
Androgens -> Oestrogens
Through which enzyme?
Aromatase
Where is Aromotase made?
Granulosa cells (follicles)
Theca Cells is where
Androgens are produced
How can the same gene be tissue specific
By having alternative promoters
Menopause
No follicles/eggs/ovarian functions
How can one gene give rise to several products?
What are the products known as?
Alternative splicing of exons
Isoforms
How can the protein be modified once made?
Post-translational modification eg phosphorylation
Glycosylation i.e. adding on carbohydrates to protein, making protein more stable and soluble
What are the DNA requirements for sexual reproduction?
Fusion of haploid cells (gametes) to create unique diploid progeny
What are the advantages of sexual reproduction?
Prevents the accumulation of genetic mutations
Increase in genetic diversity
Maintenance occurs because of the advantage of genetic variability
Better able to evolve and adapt to changing environment due to variation
Gamete
A haploid cell specialised for sexual fusion
Gametes are highly specialised cells originating from which kind of cells?
Primordial Germ Cells
Gametes are formed from germ line cells: primordial germ cells that migrate into the gonad and then differentiate to either male or female gametes.
oogenesis ? spermatogenesis?
Undergo cycles of mitosis to increase numbers
Then undergo meiosis
Then combine at fertilisation
Comparison of Mitosis & Meiosis
Mitosis?
*Involves ___ cell division
*Produces _______ ______ cells
*Occurs in ________ cells
*Results in _____ ___ _______
*Genetic material exchanged?
*Are daughter cells genetically similar?
*Involves one cell division
*Produces two diploid cells
*Occurs in somatic cells
*Results in growth and repair
*No exchange of genetic material
*Daughter cells are genetically similar
Comparison of Mitosis & Meiosis
Meiosis?
*Involves ___ cell division
*Produces up to _______ ______ cells
*Occurs in ________and _______
*Results in _____
*Genetic material exchanged?
*Are daughter cells genetically similar?
*Involves two cell divisions
*Produces up to four haploid cells
*Occurs only in ovaries and testes during the formation of gametes (egg and sperm)
*Results in gamete (egg and sperm) production
*Parts of chromosomes are exchanged in crossing over
*Daughter cells are genetically dissimilar
Why is meiosis advantageous?
- Random distribution of male and female homologous chromosomes
- chromosomal crossing over occurs
How is genetic variability achieved?
Two ways
Independent Assortment
Crossing Over (Recombination)
Independent Assortment
Homologous pairs of chromosomes line up at the equator (midpoint) of the spindle during metaphase I.
However, the orientation of the members of the pair is random with respect to which member is closer to which pole.
Crossing Over (Recombination)
Corresponding pieces of chromatids of maternal and paternal homologues (non-sister chromatids) are exchanged during synapsis when the homologues are aligned side by side.
Each of the affected chromatids has a mixture of maternal and paternal genetic information
Does Crossing Over of Sex Chromosomes occur?
Sex chromosomes align but crossing over does not usually occur in X and Y chromosomes apart from at the pseudoautsomal regions (PAR)
why doesn’t Crossing-over of sex chromosomes not usually occur?
They are hemizygous to each other & so recombination proved harmful
PAR allows the X & Y chromosomes to pair and properly segregate during meiosis in males
aneuploidy
A gain or loss of chromosomes from the normal 46
Non-disjunction
Failure of homologous chromosome to separate during MI or sister chromatids to separate during MII, resulting in extra or missing chromosomes
Most common aneuploidies in humans are _____
trisomies
Increase in Maternal Age
Increases risk of Trisomy
What are the factors of maternal age and risk of trisomy effect
Recombination failure
Premature homologue separation
Premature sister chromatid separation due to loss of cohesion between sister centromeres
