REPRODUCTION, DNA and GENETICS

gamete

a sex cell that contains half the normal chromosome number

chromosome

a long dna molecule containing many genes

gene

a small section of dna on a chromosome that codes for a partiular sequence of amino acids to make a specific protein

allele

different versions of the same gene

dominant allele

this allele is always expressed even if only one copy is present. represented by a capital letter

recessive allele

an allele that is only expressed if two/both copies are present. represented by a lower case letter

homozygous

if two alleles present are the same, individuals are said to be homozygous for that trait

heterozygous

if two alleles present are different, individuals are said to be heterozygous for that trait

genotype

describes the alleles present or genetic makeup of an individual regarding a particular characteristic

phenotype

the physical appearance of an individual regarding a particular characteristic

how many parents in sexual reproduction

2, opposite sex

how many parents in asexual

1

sexual reproduction

• genetic information

• offspring

• genetic information is mixed

• variety in offspring as reproductive cells in meiosis

asexual reproduction

• genetic information

• offspring

• no mixing of genetic information

• genetically identical offspring (clones)

• only mitosis involved

where do cells divide by meiosis

reproductive organs to produce gametes

3 stages of MEIOSIS

1. copies of genetic information are made

2. cell divides TWICE to form FOUR gametes with single set of chromosomes (haploid cells)

3. all gametes are genetically different from each other (creates variation)

what happens when gametes join

• ferilisation

• normal number chromosomes restored

• cells divide by mitosis

• cells differentiate in embryo

sexual reproduction speed and energy cost

MORE energy and time needed to reproduce (find mate+ spread gametes)

asexual reproduction speed and energy cost

LESS energy and time needed to reproduce (more efficient)

variation with sexual reproduction (why is this good)

• genetic variation in offspring

• if environment changes = survival advantage

• some will survive and reproduce

variation with asexual (pros and cons)

• no genetic variation

• many identical offspring can be produced if conditions are favourable

• vulnerable if conditions change

• if 1 individual can’t survive, none can

is artificial selection possible with sexual reproduction?

• yes

• speeds up natural selection

• used by humans in selective breeding

is artificial selection possible with asexual reproduction?

NO

organisms that reproduce w sexual + asexual

• fungi (asexual by spores, sexual for variation)

• malaria (asexual in human, sexual in mosquito)

• plants (asexual = runners, strawberry plants + daffodil bulbs. sexual = seeds)

dna is a ____ made up of _______

polymer

two strands forming a double helix

DNA monomers

• nucleotide

• phosphate group + sugar backbone

• base (at, cg)

genome

the entire genetic material of an organism

studying genome allows us to

• search for genes linked to different types of diseases

• understand and treat inherited disorders

• trace human migration patterns of the past

sequence of bases form a….

code

how many bases in a codon

3

what does a codon code for

• amino acid in a protein

• order of bases controls order of amino acid

• joined to make specific protein

what carries code for sequence of amino acid

template molecule

• coded for by genes in nucleus

• goes to ribosome

amino acids assembled by

carrier molecules (bring specific amino acids to protein chain)

what happens when chain is complete

protein folds into specific shape for job (enzyme, hormorne, structural components, antibodies)

mutation

change in the DNA base sequence

occur continuously, particularly when dna replicated

few mutations code for

altered protein with different shape, affects the shape + functionality of the protein

Non coding parts of dna…..

switch genes on and off, variations will impact whether protein is made

female chromosomes

XX

male chromosomes

XY

chance of male/female

50%

polydactyly- dominant or recessive?

dominant

what is polydactyly?

having extra fingers/toes

what genotype to not have polydacyly?

homozygous recessive

cystic fibrosis- dominant or recessive?

recessive

to have CF, what genotype?

homozygous recessive

to be carrier of CF, what genotype?

heterozygous

gene therapy

replacing faulty genes

positives of embryo screening

• reduces no. of people with disease (if aborted)

• reduces healthcare costs (if aborted)

• expensive to have babies with disease

• informed choice about abortion

• prepare financially + emotionally

negatives of embryo screening

• possible damage/risk to embryo

• possible harm/risk to mother

• screening expensive

• right to life

• ethical/moral/religious desicions about abortion