chromosomes to genomes

Question 1

DNA

Answer 1

-stands for deoxyribonucleic acid
- carries heritable information from one generation to the next.
- packed into units called chromosomes.
- tightly wound around histones

Question 2

nucleotides

Answer 2

• four different nitrogenous bases: thymine, guanine, cytosine & adenine.
• join according to base pairing rules to link two strands of DNA to make DNA molecule.
• Adenine joins to Thymine with two hydrogen bonds - Guanine joins to Cytosine with three hydrogen bonds

Question 3

DNA (structure)

Answer 3

• double helix, shaped like a spiral ladder
• Alternating phosphates and deoxyribose sugars form the sides of the ladder,
• bases forming the rungs.
• Covalent bonds (strong) join the phosphates and sugars
• nitrogen-containing bases are joined by hydrogen bonds (weak).

Question 4

Gene

Answer 4

• section of DNA which carries coded information for making a protein or an RNA molecule.
• Not all parts of DNA are coding; some parts are regulatory,
• others are true ‘junk’ such as old broken genes
• some parts have other functions
• function of some parts is not known.

Question 5

functions of non-coding DNA

Answer 5

• Assist DNA packing
• Signal to start replication of the DNA for making new cells for growth, repair or reproduction
• Assist chromosomes to align during cell division
• Stabilises the ends of the chromosomes (telomeres)
• regulatory sequences control when and for how long other genes are active.
• Regulatory sequences can be far from the genes that they control on the same chromosome or on a different chromosome.

Question 6

more about genes

Answer 6

• Specific genes can have variations in their DNA sequences.
• different versions of the same gene are called alleles.
• For some genes only one version exists so all individuals will be the same
• other genes have multiple alleles and this results in differences between individuals.

Question 7

genome

Answer 7

The genome of an organism is all of its DNA, both coding and non-coding, in a haploid cell.

Question 8

more abt genomes

Answer 8

• In eukaryotes DNA is found in the nucleus and mitochondria;
• photosynthetic eukaryotes also in chloroplasts
• study of genomes is called genomics.
• Advances in DNA sequencing technology has greatly enhanced the study of individual genomes.

Question 9

Proteomics

Answer 9

• All of the proteins in a cell is called its proteome.
• Proteomics is the study of all of the cell’s proteins, along with how they interact together.
• Together genomics and proteomics is resulting in the development of therapies

Question 10

bioinformatics

Answer 10

• computer assisted study of genes and proteins.
• involves the identification of differences between different sequences
• computer aligns the sequences and highlights similarities and differences.
• bioinformatic data collected is used to identify differences between individual people.
• data helps with the development of new drugs and treatments for disease.
• Multiple disciplines of Science and Technology are involved.

Question 11

some chromosome definitions

Answer 11

• Somatic cell – all body cells except gametes
• Gamete – a sex cell; sperm or ova in mammals
• Diploid – a full double set of chromosomes in a cell
• Haploid – a half set of chromosomes such as that in a gamete
• Homologous pair – the pair of chromosomes which carry alleles for the same genes & which pair during meiosis.
• Locus (plural : loci) – the position of a gene on a chromosome
• Autosomes – all of the chromosomes except the sex chromosomes

Question 12

chromosomes

Answer 12

• Each has a partner which contains alleles for the same genes
• At a point along the chromosome there is a constriction called the centromere.
• kinetochore - to which spindle fibres attach during cell division.
• Sister chromatids are only present in dividing cells.

Question 13

chromosomes in humans

Answer 13

• Humans have 22 pairs of autosomes.
• Autosome pairs are homologous.
• Humans normally have 2 sex chromosomes.
• Females have 2 X chromosomes.
• The X’s are homologous.
• Males have an X and a Y chromosome
• The X and Y chromosomes are not homologous
• Sex chromosomes are also known as heterosomes.

Question 14

karyotype

Answer 14

A picture of the chromosomes of an organism where the chromosomes have been paired up and arranged in order of size.

Question 15

Chromosome relation to species complexity

Answer 15

• number of chromosomes varies between species.
• Number or size of chromosomes does not have any relation to the complexity of the species metabolism.

Question 16

Polyploids

Answer 16

Organisms with more than a diploid set of chromosomes e.g
- triploid - three sets
- tetraploid - four sets
- pentaploid - five sets
- hexaploid - six sets

Question 17

mitochondrial DNA (mtDNA)

Answer 17

• Both chloroplasts and mitochondria possess DNA.
• Mitochondrial DNA (mtDNA) encodes some of the genes needed for cellular respiration.
• Both chloroplast and mitochondrial DNA are circular like the chromosomes of bacteria
• In humans mitochondria and mtDNA comes from the mother as they all derive from mitochondria in the egg.

Question 18

chloroplast DNA (cpDNA)

Answer 18

• Chloroplast DNA (cpDNA) encodes genes needed for photosynthesis
• Like mitochondria all chloroplasts derive from pre-existing chloroplasts
• Chloroplasts and mitochondria reproduce by a process similar to bacteria.

Question 19

Prokaryotic DNA

Answer 19

• Most prokaryotes have a single circular chromosome
• without histones which is attached to the inside of the plasma membrane.
• They may also contain one or more plasmids.

Question 20

plasmids

Answer 20

• are small rings of DNA which usually contain genes which are not essential to metabolism
• Multiple copies of a may be present
• Bacteria can swap plasmids with each other.
• are very useful in genetic engineering .

Question 21

meiosis

Answer 21

involves the copying (replication) of DNA followed by two sets of cell division so the daughter cells contain only one member of each homologous pair and one sex chromosome. start off haploid and end diploid

Question 22

Law of segregation

Answer 22

• The two chromosomes of a homologous pair separate end up in different gametes
• separation of maternally and paternally derived members of the homologous pair is random

Question 23

Law of independent assortment

Answer 23

How one pair of chromosomes, and hence alleles, separates is independent of how a different pair on different chromosomes separate. All combinations are possible.

Question 24

non-disjunction

Answer 24

Sometimes during meiosis chromosomal separation fails in a process

Question 25

aneuploidy

Answer 25

If a gamete carrying a chromosomal non-disjunction fuses with a normal gamete and the resulting zygote develops, the offspring will have aneuploidy
-having more or less than the normal number of chromosomes.

Question 26

polyploidy

Answer 26

• total non-disjunction occurs
• result of the failure of the spindle to form properly, or at all.
• diploid gamete is fertilised, a triploid organism develops
• two diploid gametes fuse a tetraploid organism develops.
• Polyploidy in animals is rare but is fairly common in plants.

Question 27

chromosomal errors

Answer 27

DUPLICATION:
During crossing over one member of a homologous pair can end up with two copies of a section of chromosome.
DELETION:
During cell division a section of chromosome may be lost. It may go to the homologous partner or another chromosome entirely.
INVERSION:
A section of chromosome is inverted so the DNA is read backwards.
TRANSLOCATION:
A section of a chromosome or a whole chromosome becomes attached to a non-homologous chromosome.

Question 28

gene

Answer 28

a piece of DNA which codes for a characteristic or trait.

Question 29

locus

Answer 29

position of a gene on a chromosome

Question 30

allele

Answer 30

a variation or alternate form of a gene

Question 31

phenotypes and genotypes

Answer 31

genotypes concern the letters of a gene and phenotypes are the observable and physical characteristics of a gene

Question 32

homozygous

Answer 32

having identical gene pairings

Question 33

heterozygous

Answer 33

having different gene pairings

Question 34

hemizygous

Answer 34

Males have only one allele for traits carried on either sex chromosome.

Question 35

types of inheritance

Answer 35

dominant/recessive - one is dominant and one is recessive and recessive genotypes need to be homozygous in order to be expressed
incomplete dominance - the expression of the two alleles is blended. eg red and white equals pink offspring
co-dominance - neither trait is dominant and both alleles are fully expressed.
(e.g spotting or blood types)
sex-linked - linked to most commonly the X chromosome

Question 36

epigenetics

Answer 36

Modern studies have shown that DNA can be modified during a person’s lifetime. e.g methylated DNA - stops a gene from being expressed

Question 37

test crosses

Answer 37

a cross between an individual displaying a recessive trait and one displaying a dominant trait to determine whether or not the dominant trait is heterozygous.

Question 38

pedigrees

Answer 38

autosomal recessive - of daughters have the condition, their fathers have it too
autosomal dominant - half or more of all individuals are affected by the condition
X-linked dominant - males with the condition only passes it on to daughters
X-linked recessive - condition mainly found in males
Y-linked - only in males