Genetics - Chromosomes & Karyotypes

Question 1

What are chromosomes?

Answer 1

carry genes in a linear sequence that is shared by members of a species

same # of chromosomes, same genes, same loci

structural units made of DNA and proteins

coiling DNA around proteins, large amount of info can be stored in nucleus

Question 2

what are chromosomes like in eukaryotes?

Answer 2

linear strands of DNA held in helix (~8.5 cm), to fit in nucleus diameter must be ~10hm so must be coiled to allow for processes

nucleosomes formed by wrapping DNA around 8 histone proteins

different chromosomes carry different genes

Question 3

what are chromosomes like in prokaryotes (referred to as ultrastructure bc few organelles)?

Answer 3

copy of chromosome made right before binary fission

bc only 1 chromosome, only 1 copy of each gene

can be single chromosome or in form of plasmid

Question 4

What are the features of plasmids?

Answer 4

naked, small circular DNA with no histone proteins

not responsible for normal life processes (these are controlled by nucleic chromosomes)

commonly contain survival characteristics (e.g. antibiotic resistance)

can be passed btw prokaryotes

can be incorporated into the nucleic chromosome

Question 5

What is the Cairns technique for measuring length of DNA molecules by autoradiography?

Answer 5

e.coli grown at thyme containing a radioactive isotope of H

E coli cells broken open by enzymes to release contents

cells contents applied to a photographic emulsion & placed in the dark for 2 months

radioactive isotopes reacted wt emulsion indicated presence of DNA

images showed E coli posses single circular chromosome which is 1,100hm long

Question 6

How may chromosomes vary?

Answer 6

in length - # base pairs

position of centromere

banding pattern

Question 7

What can you tell me about chromosome numbers?

Answer 7

important characteristic of a species

organisms wt different # chromosomes unlikely to interbreed successfully

chromosomes can fuse / split during evolution - rare & chromosome # tend to stay the same

chromosome # does not reflect complexity (e.g grape chromosomes > human chromosomes, “yet we eat them & they don’t eat us” - Mr Naiker, 2021

of chromosomes possessed by species known as N number

Question 8

What is the sexual life cycle?

Answer 8

most sexually reproducing organisms are diploid (2 spies of every chromosome - maternal / paternal)

to reproduce, organisms make haploid gametes (one copy / chromosome) via meiosis

fertilisation of 2 haploid gametes = diploid zygote (grows through mitosis)

if chromosome # not halved in gametes, total chromosome # would double each generation (polyploidy)

Question 9

What can you tell me about ploidy: Diploid nuclei?

Answer 9

nuclei possessing pairs of homologous chromosomes are diploid (2n)

will poses 2 gene copies (alleles) for each trait

all somatic cells will be diploid wt new diploid cells created via mitosis

present in most animals & plants

Question 10

What can you tell me about Ploidy: Haploid Nuclei?

Answer 10

possessing 1 set of chromosomes (n), single gene copy (allele) for each trait

all sex cells (gametes) are haploid, derived from diploid cells via meiosis

present also in bacteria & fungi

Question 11

What can you tell me about homologous chromosomes?

Answer 11

carry same sequence of genes but not necessarily same alleles

sexually reproducing organisms inherit genetic sequences from both parents - ORGANISM WILL POSSES 2 COPIES OF ECH CHROMOSOME - homologous chromosomes

share structural features (size, banding pattern, centromere location)
same genes at same loci

Question 12

How is sex determined?

Answer 12

sex is determined by the sex chromosomes & autosomes have no impact on sex

1 pair of heterosomes = sex chromosomes

X chromosome is larger - contains more genes in non-homologous regions

SRY gene in Y chromosome = male development

chromosome pairs segregate in meiosis

Question 13

What is a karyogram?

Answer 13

diagram / photo of chromosomes in nucleus arranged in homologous pairs of decreasing length

visible bc taken during metaphase (mitosis) and staining makes banding patterns visible

micrograph taken & chromosomes arranged based on size, shape and banding pattern

Question 14

What are karyotypes?

Answer 14

is a property of eukaryotic cells described by # & type of chromosomes in nucleus

normally prenatal to test gender & chromosome abnormalities

process where chromosomes organised & visualised for inspection

Question 15

What are the steps to make a karyogram (karyotype process)?

Answer 15

harvest cells

chemically induce cell division and arrest when chromosomes condensed

the stage which mitosis is halted determines whether chromosomes appear wt sister chromatids

stained and photographed

Question 16

What are chromosomal abnormalities?

Answer 16

if zygote formed from game experienced non-disjunction event

therefore offspring will have extra/less chromosomes in every cell of their body

Question 17

What are some examples of chromosomal abnormalities?

Answer 17

Patau’s Syndrome (trisomy 13)

Edwards Syndrome (trisomy 18)

Klinefelter Syndrome (XXY)

Turner’s Syndrome / Fragile X (monosomy X)

Downs Syndrome (trisomy 21)

Question 18

What is non-disjunction?

Answer 18

chromosomes fail to seperate correctly resulting in gametes et 1 extra/less chromosome (aneuploidy)

failure may be due to:
-failure of homologous chromosomes to seperate in Anaphase I = 4 affected haploid daughter cells

• failure of sister chromatids to seperate during Anaphase II = 2 affected haploid daughter cells

Question 19

What can you tell me about Downs Syndrome?

Answer 19

3 copes of chromosome 21 bc ! parental gamete has 2 chromosome 21

extra copy = mental & physical delays

increased probability of child wt syndrome as maternity age increases (especially after 30)