chapter 7 - genetics

Question 1

gene

Answer 1

a particular section of DNA that codes for the creation of an individual polypeptide chain

Question 2

genome

Answer 2

collection of genes which houses all genetic info to build and maintain

Question 3

alleles

Answer 3

different forms of same gene but with small differences in base sequence

Question 4

criteria for homologous chromosomes

Answer 4

-they are the same size and length
-they have the same centromere position
-they share the same genes at the same gene loci

Question 5

autosomes

Answer 5

pairs labelled 1-22 on a karyotype

Question 6

sex chromosomes

Answer 6

pair labelled X and Y (XX - female, XY - male)

Question 7

aneuploidy

Answer 7

abnormality where there is an incorrect number of total chromosomes caused by the addition or loss of an individual chromosome

Question 8

monosomy

Answer 8

one missing chromosome (2n-1)

Question 9

trisomy

Answer 9

one extra chromosome (2n+1)

Question 10

tetrasomy

Answer 10

two extra chromosomes (2n+2)

Question 11

polyploidy

Answer 11

chromosomal abnormality in which an organism has more than two sets of each chromosome

Question 12

meiosis

Answer 12

a specialised form of cell division occurring in sexually reproducing organisms, used to produce gametes

Question 13

divisions of meiosis

Answer 13

-meiosis 1: separates each homologous chromosome into different cells
-meiosis 2: separates each sister chromatid into four different cells

Question 14

stages in meiosis 1

Answer 14

-interphase: identical to mitosis
-prophase 1: chromosomes condense and thicken, crossing over occurs
-metaphase 1: chromosomes line up on metaphase plate, independent assortment occurs
-anaphase 1: chromosomes are moved apart
-telophase 1: chromosomes are on opposite ends of cell

Question 15

stages in meiosis 2

Answer 15

-prophase 2: chromosomes condense
-metaphase 2: chromosomes line up on metaphase plate
-anaphase 2: sister chromatids are separated, pulled towards opposite sides
-telophase 2: membrane forms
-cytokinesis: splits each set of chromosomes into four individual cells

Question 16

crossing over

Answer 16

when genetic material is exchanged

Question 17

independent assortment

Answer 17

random arrangement of homologous chromosomes, splitting into two random daughter cells

Question 18

homozygous

Answer 18

alleles inherited from parents are identical

Question 19

heterozygous

Answer 19

alleles inherited from parents are different

Question 20

dominant allele

Answer 20

stronger form of a pair of alleles - always expressed if present

Question 21

recessive allele

Answer 21

weaker form of a pair of alleles - only expressed if individual has two copies of allele

Question 22

complete dominance

Answer 22

when a dominant allele is fully expressed in a phenotype

Question 23

codominance

Answer 23

when both alleles from the genotype are fully expressed in the phenotype of a heterozygote (both are dominant)

Question 24

incomplete dominance

Answer 24

when neither allele is fully expressed in a phenotype (observable trait is a blend of both alleles)

Question 25

proportionate heritability

Answer 25

phenotype is partly explained by genes and partly by environmental factors

Question 26

epigenetics

Answer 26

changes to an organism’s phenotype resulting from modifications to gene expression

Question 27

transcription

Answer 27

-involves reading and copying out a gene sequence from a DNA molecule
-this copy (mRNA) then moves out of the nucleus to ribosomes in the cytosol on the rough endoplasmic reticulum for translation

Question 28

translation

Answer 28

after transcription, mRNA instructs the ribosome how to build the specific protein for which the DNA sequence codes

Question 29

how does epigenetics relate to transcription?

Answer 29

-epigenetic changes alter the process of transcription
-they are caused by molecules that increase or decrease the amount of transcription of a particular gene and therefore alters the amount of protein produced

Question 30

how do environmental factors change phenotype?

Answer 30

-environmental factors may cause changes to a gene that activate or deactivate the expression of that gene
-this affects the amount of protein produced, which therefore alters an individual’s phenotype

Question 31

types of epigenetic changes

Answer 31

-dna methylation/demethylation
-histone modification

Question 32

dna methylation/demethylation

Answer 32

-dna methylation refers to when methyl groups attach to certain nucleotides within the DNA sequence of a particular gene and alters levels of gene expression, typically by causing that gene to be silent
-dna demethylation refers to the removal of methyl groups from a DNA sequence, and typically leads to the gene being expressed

Question 33

histone modification

Answer 33

-occurs when histone modifying enzymes (HMT - histone methyltransferases) join methyl groups to histone tails and modify how tightly the dna molecule is wrapped around it

-if the dna is condensed tighter around the histone, it makes it difficult for the protein to be transcribed and less likely to be expressed
- If the DNA is less tightly packed, the genes will be easier to transcribe and more likely to be expressed

Question 34

why is epigenetics important?

Answer 34

-helps to control cell differentiation - the development of different cell types is regulated largely due to epigenetic mechanisms that turn off unneeded genes and promote expression of required genes

-provides a mechanism for a developing organism to respond to its environment - acts as a rapid feedback mechanism by which an organism can respond to changes in their environment

Question 35

epigenetics inheritability

Answer 35

-epigenetic changes can be passed onto daughter cells during mitosis
-epigenetic features are somatically inheritable - able to be passed from somatic cell to somatic cell indefinitely across the individual’s lifespan
-most epigenetic changes in an organism are erased when gametes are formed - however a small proportion of these changes can remain during gamete production