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OCR Gateway A GCSE Biology > B5: Genes, inheritance and selection > Flashcards

B5: Genes, inheritance and selection Flashcards

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1
Q

what is variation

A
  • the difference between individuals of the same species
    or
  • differences within species
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2
Q

what is variation caused by

A
  • genetic + environmental factors
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3
Q

what is a phenotype

A
  • the appearance of an organism or how the alleles are shown
    > can be affected by your environment
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4
Q

what is genetic / inherited variation + give examples

A
  • genetic material you inherit from your parents
  • examples:
    > eye colour
    > hair colour
    > blood group
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5
Q

what is environmental variation + give examples

A
  • the environment in which you live in and how it can affect your characteristics
  • examples:
    > scars
    > intelligence
    > suntan
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6
Q

what is discontinuous variation + example

A
  • when the characteristics fall into distinct / definite categories with no in-between
    > examples - blood group, eye colour
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7
Q

what is continuous variation + example

A
  • when the characteristic can be any value in a complete range of phenotypes from one extreme to the other
  • no distinct categories
    > examples - height in humans
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8
Q

what’s the causes of discontinuous / continuous variation

A
  • discontinuous = genetic
  • continuous = genetic + environmental
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9
Q

how many genes control discontinuous / continuous variation

A
  • discontinuous = one (or few genes)
  • continuous = multiple genes
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10
Q

what happens to offspring in asexual reproduction

A
  • offspring get all their genes from one parent
    > they are genetically identical to the parent - natural clones
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11
Q

what is a clone

A
  • an organism that is genetically identical to its parent
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12
Q

what does asexual reproduction not require

A
  • sex cells (gametes)
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13
Q

how does asexual reproduction occur

A
  • an individual replicates their genetic material + divides in half (mitosis)
    > the new organisms are clones
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14
Q

many ____ reproduce asexually

A
  • plants
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15
Q

explain how strawberries reproduce

A
  • reproduce asexually
  • they send runners (long stems) over the ground
  • the runners sprout roots at various intervals + new plants grow
  • once the plants are established, the runners die and rot away
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16
Q

why are plants more likely to reproduce asexually

A
  • because they retain their stem cells, whereas in animals the stem cells aren’t retained and differentiate
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17
Q

what happens to the offspring in sexual reproduction

A
  • the offspring gets genes from two parents
    > they will inherit a mixture of features from both parents
    > offspring not genetically identical
  • each parent gives half of the genes to the offspring
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18
Q

most ____ reproduce using sexual reproduction

A
  • animals
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19
Q

what are gametes

A
  • sex cells
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20
Q

what are the 2 gametes

A
  • sperm (male)
  • egg (female)
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21
Q

how does sexual reproduction work

A
  • organisms produce sex cells (gametes - egg + sperm) (haploid)
  • the nucleus of sperm egg fuses with nucleus of egg + egg is fertilised (zygote - diploid)
  • the fertilised egg divides (mitosis) + grows in the uterus + develops into the offspring
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22
Q

in what case would plants reproduce sexually + how

A
  • to create a new seed, which will grow into a plant
  • pollen cell (male sex cell) fuses with an egg cell (female sex cell) in the ovule
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23
Q

what are the gametes in plants

A
  • pollen cell (male)
  • egg (female)
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24
Q

what are some advantages of asexual reproduction

A
  • is parent is well adapted to an area, the offspring will be too
  • only one parent needed - animals don’t need to find partner + pollination not needed in plants
    > organisms can reproduce whenever they want (or when conditions are favourable) without waiting for a partner
  • faster reproduction - so larger number of offspring produced quickly
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25
Q

what is a disadvantage of asexual reproduction

A
  • no genetic variation
  • if there’s any adverse changes to the environment, it may destroy the species + all organisms will be affected
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26
Q

what is an advantage of sexual reproduction

A
  • variation in offspring leads to adaptations in species
    > some organisms will have adaptations required to cope with an environmental pressure + these organisms can reproduce allowing the population to continue
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27
Q

what are some disadvantages to sexual reproduction

A
  • requires 2 parent
    > can be problem if organisms are isolated
  • slower - so resulting in fewer offspring
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28
Q

how many chromosomes are there in most human body cells

A
  • 46 - diploid number
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29
Q

how many chromosomes do gametes contain

A
  • 23
    > haploid number
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30
Q

why do gametes have half the number of chromosomes

A
  • have 23 chromosomes so that during fusion, the zygote has 46 chromosomes
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31
Q

what are diploid cells

A
  • normal body cells with 48 chromosomes
    or
  • diploid cells have a nucleus containing 2 sets of chromosomes
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32
Q

what are haploid cells

A
  • gametes - they have half the number of chromosomes - only one of each
    or
  • haploid cells have a nucleus containing a single set of unpaired chromosomes
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33
Q

what is mitosis

A
  • it occurs in all living body cells + asexual reproduction
  • produces 2 genetically identical daughter cells
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34
Q

what is a genome

A
  • the entire genetic material of an organism
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35
Q

how are genomes affected by sexual reproduction

A
  • all individuals produced by sexual reproduction have a unique genome
    > except for identical twins
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36
Q

how are gametes made

A
  • by a type of cell division called meiosis
    > 4 haploid cells are produced from 1 diploid parent cell
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37
Q

describe the 2 main stages of meiosis

A

stage 1:
- chromosomes copied
- chromosomes line up along middle of cell in pairs (one from each parent)
- 1 member of each pair is pulled to opposite ends of the cell (when pulled apart, often sections of DNA are swapped)
- cell divides into 2
- 2 separate cells are formed
stage 2:
- chromosomes line up along the middle of each of the 2 new cells
- this time each chromosome is pulled in half - a single copy of each chromosome goes to opposite ends of the cell
- each cell then divides into 2 - resulting in 4 haploid cells

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38
Q

how many times does a cell divide during meiosis

A
  • 2
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39
Q

what does meiosis result in

A
  • cells that are genetically different from each other + from the parent cell
    > not genetically identical
  • creates genetic variation
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40
Q

what is a chromosome

A
  • a long strand of DNA, coiled up, carrying genetic information in the form of genes
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41
Q

what is a gene

A
  • a section of DNA that codes for a specific protein
    > can be copied + passed onto next generation
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42
Q

what is an allele

A
  • a different version of a gene
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43
Q

how many copies of each gene per characteristic do you have + why

A
  • 2 copies of every gene for each characteristic
    > 1 from each of your parents
    > these copies may be the same or could be different
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44
Q

what is a genotype

A
  • the combination of alleles present in an organism
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45
Q

how are genotypes represented

A
  • by 2 letters that are either dominant/ recessive + homozygous/heterozygous
46
Q

what does it mean if a characteristic is homozygous

A
  • you have 2 identical alleles for a characteristic
    > e.g. BB or bb
47
Q

what does it mean if a characteristic is heterozygous

A
  • you have 2 different alleles for a characteristic
    > e.g. Bb
48
Q

what is a dominant allele

A
  • the more stronger allele that will always show up in the phenotype
    > you only need one copy of a dominant allele for the characteristic to be expressed
49
Q

what is a recessive allele

A
  • the weaker allele that only shows up if you have two copies (homozygous )
50
Q

how are dominant + recessive alleles represented

A
  • dominant = capital letter e.g. B
  • recessive = lower case of the same letter e.g. b
51
Q

how do you predict genetic crosses

A
  • state phenotype of both parents
  • state genotype of both parents
  • state gametes of each parent - circle the letters
  • use a Punnett square
52
Q

how many pairs of sex chromosomes do human cells contain

A
  • 1 pair
53
Q

what do sex chromosomes control

A
  • your sex
54
Q

what is the 23rd pair of chromosomes in humans known as

A
  • sex chromosomes
55
Q

what are the chromosomes for males

A

XY (heterozygous)

56
Q

what are the chromosomes for females

A

XX (homozygous)

57
Q

what determines the sex of an offspring

A
  • male gametes (sperm)
  • females only produce X gametes, so its the sperm that determines the sex
58
Q

draw a Punnett square for determining the sex of a human offspring

A

I X I Y
——————————————- 50:50 ratio
X I XX I XX of boy : girl
Y I XY I XY

59
Q

when does a mutation occur

A
  • when the sequence of DNA bases is altered
60
Q

mutations occur ______

A
  • spontaneously (randomly)
    > e.g. DNA may not replicate correctly
61
Q

do mutations affect phenotype

A
  • most don’t affect phenotype
  • some may influence phenotype
  • a few will determine phenotype
62
Q

are mutations that affect an organism’s phenotype harmful + examples

A
  • most are harmful
    > can cause: cancer, cystic fibrosis, sickle cell anaemia
  • some are neutral - they neither harm/benefit the individual
    > freckles, tongue rolling etc.
  • few are beneficial
    > malaria resistance, antibiotic resistance
63
Q

what increases the chances of mutations

A
  • some chemicals
    > benzene + ethanol
  • ionising radiation
    > ultraviolet from sun, x-rays
64
Q

how can mutations influence an organism’s phenotype in coding DNA

A
  • mutation alters the activity of proteins:
  • if mutation occurs within a gene, DNA bases may be changed, added or deleted
  • this changes the sequence of bases
  • the order of mRNA bases are changed + so the order of amino acids may change
  • this means that the protein produced may fold incorrectly + form a different shape
    > protein structure is changed
65
Q

give an example of mutations altering an organisms phenotype in coding DNA

A
  • if protein is an enzyme, it’s active site may change shape
  • substrate no longer binds + can’t catalyse a specific chemical reaction
    > enzyme no longer works
  • can result in metabolic diseases e.g. phenylketonuria —> phenylalanine can’t be broken down by body —-> brain damage
66
Q

what is a genetic variant

A
  • a different version of a gene
67
Q

what do mutations produce

A
  • a genetic variant
68
Q

what is non-coding DNA

A
  • DNA bases that don’t code for proteins
69
Q

how does mutation of non-coding DNA influence the phenotype

A
  • it can affect how genes are expressed:
  • there are specific sequences of DNA bases found before a gene which triggers the process of transcription
    > they’re located within the non-coding sections of DNA
  • if mutation occurs within this sequence, the gene may not be transcribed into mRNA (stops transcription of mRNA)
    > this means the protein the gene codes for will not be produced
70
Q

what are most phenotypic features results of

A
  • multiple genes rather than single gene inheritance
71
Q

what did Gregor Mendel carry out an experiment on (1866)

A
  • peas
72
Q

what did Mendel observed in his experiment

A
  • that characteristics such as height + colour are passed on from parents to offspring
73
Q

what were the 3 big findings in Mendel’s experiment

A
  • characteristics were determined by hereditary units (now called genes)
  • genes passes on from both parents, one from each
  • genes are dominant / recessive
74
Q

what is classification

A
  • the process of sorting living organisms into groups that share similar features
75
Q

why do scientists classify organisms

A
  • to identify species
  • to predict characteristics
  • to find or show evolutionary links
76
Q

what is one of the way scientists classify organisms

A
  • classify organisms at 7 taxonomic levels
77
Q

what are the 7 taxonomic levels + the acronym for it

A
  • King Phillip Cried Out For Good Soup
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
78
Q

what happens as you go down the taxonomic levels

A
  • the organisms share more characteristics
79
Q

what are the 5 kingdoms

A
  • plants
  • animals
  • fungi
  • protoctista (amoeba + algae, no nucleus)
  • prokaryotes (single celled, no nucleus)
80
Q

what is a species

A
  • a group of organisms that is able to reproduce to produce fertile offspring
  • species is the lowest level of classification + is one type of organism
81
Q

what is a Binomial nomenclature

A
  • its a way to name species
  • known as binomial as it has 2 parts:
    > Genus name - capital letter
    > species name - lower case
82
Q

what is artificial classification

A
  • organisms are grouped based on observable characteristics
83
Q

what is the problem with artificial classification

A
  • has caused problems in accurate classification as some species may look different but be closely related
84
Q

what is natural classification

A
  • new development have led to changes in the classification system
  • DNA sequencing is used to link evolutionary relationships + identify common ancestors
    > the more similar the DNA, the more closely related the species
85
Q

what is phylogeny

A
  • the study of evolutionary links
86
Q

how are phylogenic links established

A
  • by studying similarities ( + differences) in DNA between species
    > the more similar the DNA, the more closely related the species are
87
Q

what has led changed to the classification system

A
  • new development
  • new scientific discoveries
88
Q

what is DNA sequencing used to link

A
  • evolutionary relationships
    + identify common ancestors
89
Q

what is evolution

A
  • the gradual change in a species over time (millions of years)
    or
  • the change in the inherited characteristics of a population over time, through a process of natural selection, which may result in the formation of a new species
90
Q

what increases genetic variation

A
  • mutations cause new forms of genes which adds variation
90
Q

what have scientists thought to be the most common ancestor of all organisms

A
  • unicellular aquatic organisms (similar to bacteria) that lived over 3 billion years ago
91
Q

how do organisms evolve

A
  • through the process of natural selection
92
Q

how is genetic variation helpful

A
  • the genetic variation could give an individual a competitive advantage over the other members of it species
  • it’s more likely to survive + reproduce + pass on the mutated gene to the next generation
    > known as survival of the fittest
92
Q

give an example of evolution

A
  • peppered moths:
  • in early Britain they were pale (C19th)
    > this helped camouflage them against trees + mutated moths with dark colour were easily spotted + eaten
  • during industrial revolution trees became covered in soot, turning bark black
    > now black moths were more camouflaged + more of them survived
  • now dark peppered moths are more common in urban areas
92
Q

describe how natural selection occurs (steps)

A
  • individuals in species show genetic variation
  • best adapted individuals are more likely to survive + reproduce (survival of the fittest)
  • the ‘successful’ genes are passed to the offspring in the next generation
  • offspring are more likely to have the ‘successful’ characteristic
  • over time this can leas to the development of a new species
93
Q

explain how antibiotic-resistant bacteria can evolve

A
  • bacteria can reproduce rapidly
  • if mutation occurs, bacterium usually dies
  • sometimes it could give the bacteria resistance to antibiotics
  • now the non-resistant bacteria will be killed but the antibiotic-resistant bacteria will live + reproduce passing on the antibiotic resistance
  • eventually the whole species will become antibiotic resistant
93
Q

what are fossils

A
  • fossils are made when animals + plant remains are preserved in rock
94
Q

what is the fossil record

A
  • the fossil layers form a sequence showing that organisms have gradually changed over time
  • top layer of rock has recent organisms
    = the lower the layers, the older the organism
95
Q

how do fossil records provide evidence for evolution

A
  • oldest rocks = more simple, single-celled organisms (e.g. bacteria) + newest rocks = more complex organisms (e.g. vertebrates)
    > supports theory that simple life forms gradually evolved into more complex ones
  • plant fossils appear before animals - they’re at the bottom of food chain as animals eat them for survival
  • closely related organisms will share similarities in anatomy e.g. bone structure + scientists can show how modern day species are related to species that are now extinct
96
Q

why are there gaps in the fossil record

A
  • many organisms are soft-bodied + decompose quickly before they have a chance to fossilise
  • they can easily be destroyed (e.g. volcanoes)
  • most are usually found in the sea
  • they are deep down in rocks
97
Q

what other evidence is there for evolution

A
  • extinction - species that don’t adapt to environmental changes die out - more than 99% of all species that have ever lived are now extinct
  • molecular comparison (phylogenetics) - DNA sequence + protein structure is looked at - species that are closely related will have similarities in these molecules
  • rapid change in a species - bacteria replicating rapidly allows scientists to study evolution in action - they can see how an advantageous characteristic (e.g. antibiotic resistance) becomes common in a bacterial population
98
Q

what did people believe in Darwin’s time

A
  • 1809 - that all species on Earth were created by God
99
Q

where + what evidence did Charles Darwin collect about his theory

A
  • Galapagos Islands (Spain)
  • made observations on finches
  • noticed that different islands had different finches
    > the birds were closely related but their beaks + claws had different shapes + sizes
100
Q

what conclusion did Darwin come about his observings

A
  • that the design of the finches’ beaks was linked to food available on each island
  • concluded that a bird’s beak more suitable to the food would survive longer than a bird with a less suitable
    > it would have more offspring + pass on its beak characteristics
    > overtime all the finches on that island would share the characteristic
  • Darwin called this process natural selection
101
Q

what was the name of Darwin’s theory

A
  • Evolution and natural selection
102
Q

who was the other scientists that observed the theory of natural selection and evolution (not Darwin)

A
  • Alfred Russel Wallace
103
Q

what + where did Alfred Wallace carry out his observations on the theory of natural selection and evolution

A
  • Borneo
  • observed bird winged butterflies - realised all species are connected
104
Q

what was the name of the book Darwin published + when

A

1859 - ‘Origin of species’

105
Q

what book did Wallace publish

A

‘Darwinism’

106
Q

was the work of Darwin + Wallace accepted

A
  • scientists accepted + agreed with the work
  • public didn’t - the theory conflicted with the belief that God made all things
107
Q

Is Darwin’s theory of evolution accepted now + why

A
  • yes it’s widely accepted
  • because there’s an increasing amount of evidence to support his theory
    > fossil record, observations of microorganisms, extinctions + recent advanced in DNA studies
108
Q

did Darwin + Wallace work together

A
  • no
  • but their work was so similar they both proposed the theory of evolution through a join presentation of two scientific papers to the Linnean Society of London in 1858

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