B13 - Reproduction Flashcards
What happens in sexual reproduction? Give some examples of where it occurs:
-fusion of male + female gametes, with mixing of genetic information to produce variety in the offspring
-sperm/egg cells in animals
-pollen/egg cells in flowering plants
Give some advantages of sexual reproduction:
-we can use it to speed up natural selection with selective breeding to increase food production
-variation produced in offspring
-gives survival advantages by natural selection if the environment changes
What does asexual reproduction involve?
-1 parent reproducing by mitosis with no fusion of gametes
-leads to genetically identical offspring (clones)
Give 3 advantages of asexual reproduction:
-occurs faster
-time/energy efficient, as no need to find a mate (only 1 parent needed)
-many identical offspring can be produced when conditions are favourable
What is the difference between the products of mitosis and meiosis?
Give numbers of chromosomes
-mitosis forms 2 genetically identical diploid cells with 46 chromosomes each (23 homologous pairs)
-meiosis forms 4 genetically varied gamete haploid cells with 23 chromosomes each
Give 2 similarities between mitosis and meiosis:
-DNA gets replicated in both
-number of sub-cellular structures increase in both (mitochondria/ribosomes)
What causes the cells produced in mitosis to be genetically identical?
DNA gets duplicated
Explain how chromosomes are arranged in the cell’s nucleus:
the cell has one of each type of chromosome from the mother and the father, and is arranged into 23 homologous pairs (46 individual chromosomes)
When genetic material is duplicated, what does that actually mean in terms of chromosomes?
-each chromosome from the homologous pair makes another identical arm connected to it
-the number of individual chromosomes stays the same though
Describe the process of meiosis:
-genetic info is duplicated
-homologous pairs line up along the middle of the cell and separate (rather than each chromosome lining up) into 2 cells
-in each cell, their 2-armed chromosomes line up along the middle and each arm separates from each other
-both cells divide again, forming 4 non-identical haploid cells
Name 3 specific examples of organisms that reproduce by both sexual and asexual methods:
-malaria parasites - asexually in human host, sexually in mosquito
-most fungi - asexually by spores, and sometimes sexually to give variation
-most plants - asexually by runners (in strawberries) or bulb division (in daffodils), and sexually by seeds
Bluebells can reproduce sexually by seeds - explain why this would prove to be a survival advantage for them:
-genetic variation so the better-adapted survive
-can colonise new areas by seed dispersal
-can escape adverse event in original area by continuing to live in other areas
How is genetic information stored in a body cell? Describe its structure:
-in DNA, a 2-chained polymer of 4 different nucleotide monomers with a double helix shape
-within thread-like structures called chromosomes
-all the chromosomes make up the genome
What is the genome?
the entire genetic material of an organism
Why is it important to understand the human genome?
-can diagnose/treat inherited disorders
-can trace human migration patterns from the past
-can search for genes linked to different types of diseases
Describe the structure of a nucleotide:
-common sugar, with a phosphate group attached on its back
-one of 4 bases (ATGC) attached to the sugar
How is a gene used to code for a protein?
-DNA strand unwinds and “unzips”, and a template molecule makes a complementary copy of the gene, which then leaves the nucleus through a nuclear pore and reaches a ribosome that attaches to it
-reads template molecule 3 bases at a time and a carrier molecule brings the specific amino acid to the correct spot, and this repeats for every 3 bases until the end
-all the AAs bonds to each other
-final AA chain separates from template molecule and folds up into a functional protein
U is used in template molecule (mRNA) instead of T
What is a genetic mutation?
a random change to a base in the DNA that can change the shape/function of the protein it’s gene forms
Name some types of genetic mutations:
-substitution (a base is changed)
-insertion (base is added causing frame shift)
-deletion (base is removed causing frame shift)
A mutation has occured in this base sequence, describe how it will affect the protein it will form:
-3 bases code for 1 amino acid
-middle of CTC is now CAC, subsitution mutation
-different amino acid placed in chain
-resulting protein will have a different shape due to a different sequence of amino acids
Why is the order of bases in a gene important?
-they code for a sequence of amino acids
-the order of the 3 bases will determine the specific amino acid made
-having different amino acids will change the protein made
What is non-coding DNA? How can they be affected?
-parts of the DNA (99% of it) that doesn’t code for a protein, and instead regulate whether certain genes are expressed (turned into a protein)
-mutations in these areas can affect how genes are expressed
eg the gene for producing HCl in the eyes would be turned off, but it would be turned on in the stomach
Describe how non-coding parts of DNA can affect the expression of genes:
they can switch genes on and off
What is an allele?
different forms of the same gene
What are the 2 types of alleles, and why do we have them?
-dominant (always expressed even if only 1 of the alleles are inherited)
-recessive (expressed only if both copies are present)
-we have 2 copies of each gene (alleles) because we inherit one from both of our parents
What are characteristics controlled by, and what is the technical name for an expressed characteristic?
-a characteristic is controlled by one or more genes, where each gene can have a different form (alleles)
-the pair of alleles (eg Dd) is the genotype, and it determines an organism’s characteristic
-the characteristic expressed is known as the phenotype
Name and describe 2 inherited disorders:
polydactyly - (dom. allele) extra fingers or toes
cystic fibrosis - (rec. allele) a disorder of cell membranes that results in lots of thick + sticky mucus being produced in lungs/pancreas
Poly. has a d so it is dom., and fibrosis has an r so it is rec.
What is embryo screening?
the process of checking whether an embryo has any genetic disorders by looking at its chromosomes
Give some pros and cons of embryo screening:
-reduces overall suffering as there is less people with disorders
-saves money since genetic disorders are expensive to treat
-ethical (implies that they are less desirable)
-could lead to screening for other traits to select those with more desirable traits
-expensive process
What is the function of the 23 pairs of chromosomes in a body cell?
-22 control the characteristics that get expressed
-the last pair (sex chromosomes) determines the sex of the person
-females are XX
males are XY
