Topic 3 - Genetics Flashcards
What is sexual reproduction?
Reproduction involving production of gametes by meiosis
What happens during sexual reproduction?
A gamete from each parent fuses to form a zygote.
Genetic info from each gamete is mixed - zygote = unique.
What are gametes?
Sex cells (sperm cells/egg cells) Haploid (half no of chromosomes)
What is meiosis?
Form of cell division involved in formation of gametes
Chromosome number is halved
Involves 2 divisions
What must occur prior to meiosis?
Interphase
Why is meiosis important for sexual reproduction?
Increases genetic variation
Ensures resultant zygote is diploid
Advantages of sexual reproduction?
Creates genetic variation, increasing probability of species adapting to and surviving environmental changes
Disadvantages of sexual reproduction
2 parents needed. Makes difficult in endangered populations or species which exhibit solitary lifestyles.
More time + energy required = fewer offspring produced.
What is asexual reproduction?
Type of reproduction
Involves mitosis
Produces genetically incentivar offspring known as daughter cells
Advantages of asexual reproduction ?
Only 1 parent needed
Lots of offspring produced in short time - enables rapid colonisation of area + reduce competition from other species
Requires less emergy
Disadvantage of asexual reproduction?
No genetic variation (except spontaneous mutations) reducing probability of species being able to adapt to environmental changes.
What type of reproduction is meiosis used for?
Sexual
What is DNA
Double stranded polymer of nucleotides, wound to form a double helix
What are the monomers of DNA?
Nucleotides
What are DNA nucleotides made up of?
Common sugar
Phosphate group
One of 4 bases - A T C G
State the full names of the 4 bases found in nucleotides
Adenine
Thymine
Cytosine
Guanine
Describe how nucleotides interact to form a molecule of DNA
Sugar + phosphate molecules join to form sugar-phosphate backbone in each strand.
Base connected to each sugar.
Complementary base pairs joined by weak hydrogen bonds.
Define genome
The entire genetic material of an organism
What is a chromosome?
A long coiled molecule of DNA that carries genetic info in form of genes
Define gene
A section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
Describe the method used to extract DNA from fruit
- Place piece of fruit in beaker + crush
- Add detergent + salt. Mix.
- Filter mixture + collect liquid in test tube
- Pour chilled ethanol into test tube
- DNA precipitates forming a fibrous white solid
- Use glass rod to collect DNA sample
Why is detergent added to crushed fruit?
Disrupts cell membranes, releasing DNA into solution
Why is salt added to the crushed fruit?
Encourages precipitation of DNA
Why is chilled ethanol added rather than water?
DNA is insoluble in ethanol, encouraging its precipitation.
What did Mendel study?
He studied inheritance of diff phenotypes of pea plants.
What did Mendel establish a correlation between?
Parent and offspring phenotypes
What did Mendel note about inheritance?
It was determined by ‘units’ passed on to descendants
What is a mutation?
Random change in base sequence of DNA resulting in genetic variants
What’s the effect of a gene mutation in coding DNA?
If mutation changes amino acid sequence, protein structure + function may change
What is non-coding DNA
DNA which doesn’t code for protein but controls gene expression
Why was Mendel work overlooked initially?
Scientists didn’t understand it as there was no knowledge of genes or DNA at the time
What is a chromosome?
Long coiled molecule of DNA that carries genetic info in form of genes
Define gene
A section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
What are alleles?
Different versions of the same gene
Define genotype
An organisms genetic composition, describes all alleles
Define phenotype
An organisms observable characteristics due to interactions of the genotype + environment
Define homozygous
Having 2 identical alleles of a gene
Eg: FF or ff
Define heterozygous
Having 2 different alleles of a gene
Eg: Ff
What is a dominant allele?
Describes an allele that is always expressed
Represented with capital letter (F)
What is a recessive allele?
Allele that is only expressed in the absence of a dominant allele
Represented with small letter (f)
What is a monohybrid inheritance?
Inheritance of a single gene
What is the problem with single gene crosses?
Most characteristics are controlled by multiple alleles rather than just one
What are sex chromosomes?
A pair of chromosomes that determine sex:
Males = XY
Females = XX
Why does the inheritance of a Y chromosome mean that an embryo develops into a male?
Testes development in an embryo is stimulated by a gene present on the Y chromosome
A couple have a child. What’s the probability that the child is female?
50% chance
How can monohybrid inheritance be represented, other than a punnet square?
Family pedigree
What is a sex-linked characteristic?
A characteristic that is coded for by an allele found on a sex chromosome
What is co-dominance?
When 2 dominant alleles are expressed together in same individual
When are multiple alleles present?
When 3 or more alleles are present at same loci
An example of co-dominance/multiple alleles?
ABO blood group system
Is the O allele recessive or dominant?
Recessive
What are the A and B alleles?
Dominant
