Chromosomes and Genes

Question 1

What is the defining feature of all evolving living organisms

Answer 1

The ability to reproduce

Question 2

Karyotype

Answer 2

number and appearance of human chromosomes

Question 3

For genes to be functional DNA must be able to (three things)

Answer 3

• replicate
• separate its 2 copies at mitosis
• maintain itself between generations

Question 4

Chromosome Abnormalities

Monosomy

Answer 4

Missing Chromosomes

Question 5

Chromosome Abnormalities

Trisomy

Answer 5

Extra Chromosomes

Question 6

Down Syndrome

Answer 6

Trisomy 21

Question 7

Turner Syndrome

Answer 7

45X

One X no Y or X

Question 8

Klinefelter syndrome

Answer 8

47XXY

Extra X

Question 9

Edwards Syndrome

Answer 9

Trisomy 18

Question 10

Patau Syndrome

Answer 10

Trisomy 13

Question 11

Androgens -> Oestrogens

Through which enzyme?

Answer 11

Aromatase

Question 12

Where is Aromotase made?

Answer 12

Granulosa cells (follicles)

Question 13

Theca Cells is where

Answer 13

Androgens are produced

Question 14

How can the same gene be tissue specific

Answer 14

By having alternative promoters

Question 15

Menopause

Answer 15

No follicles/eggs/ovarian functions

Question 16

How can one gene give rise to several products?

What are the products known as?

Answer 16

Alternative splicing of exons

Isoforms

Question 17

How can the protein be modified once made?

Answer 17

Post-translational modification eg phosphorylation

Glycosylation i.e. adding on carbohydrates to protein, making protein more stable and soluble

Question 18

What are the DNA requirements for sexual reproduction?

Answer 18

Fusion of haploid cells (gametes) to create unique diploid progeny

Question 19

What are the advantages of sexual reproduction?

Answer 19

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

Question 20

Gamete

Answer 20

A haploid cell specialised for sexual fusion

Question 21

Gametes are highly specialised cells originating from which kind of cells?

Answer 21

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

Question 22

Comparison of Mitosis & Meiosis

Mitosis?

*Involves ___ cell division
*Produces _______ ______ cells
*Occurs in ________ cells
*Results in _____ ___ _______
*Genetic material exchanged?
*Are daughter cells genetically similar?

Answer 22

*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

Question 23

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?

Answer 23

*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

Question 24

Why is meiosis advantageous?

Answer 24

• Random distribution of male and female homologous chromosomes
• chromosomal crossing over occurs

Question 25

How is genetic variability achieved? Two ways

Answer 25

Independent Assortment Crossing Over (Recombination)

Question 26

Independent Assortment

Answer 26

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.

Question 27

Crossing Over (Recombination)

Answer 27

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

Question 28

Does Crossing Over of Sex Chromosomes occur?

Answer 28

Sex chromosomes align but crossing over does not usually occur in X and Y chromosomes apart from at the pseudoautsomal regions (PAR)

Question 29

why doesn't Crossing-over of sex chromosomes not usually occur?

Answer 29

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

Question 30

aneuploidy

Answer 30

A gain or loss of chromosomes from the normal 46

Question 31

Non-disjunction

Answer 31

Failure of homologous chromosome to separate during MI or sister chromatids to separate during MII, resulting in extra or missing chromosomes

Question 32

Most common aneuploidies in humans are _____

Answer 32

trisomies

Question 33

Increase in Maternal Age

Answer 33

Increases risk of Trisomy

Question 34

What are the factors of maternal age and risk of trisomy effect

Answer 34

Recombination failure Premature homologue separation Premature sister chromatid separation due to loss of cohesion between sister centromeres