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Edexcel - Biology > Chapter 3 - Genetics > Flashcards

Chapter 3 - Genetics Flashcards

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1
Q

Sexual Reproduction

A
  • Produces genetically different cells
  • Genetic information from two organisms are combined to produce genetically diiferent offspring
  • The father and mother produce gametes (reproductive cells), these are sperm and egg cells
  • Gametes only contain half the number of chromosomes of normal cells, these are called haploids
  • Normal cells are called diploids
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2
Q

Fertilisation

A
  • A male gamete fuses with a female gamete to produce a zygote
  • The zygote ends up with a full set of chromosomes
  • The zygote is a diploid
  • The zygote undergoes cell division by mitosis and develops into an embryo
  • The embryo inherits a mixture of characteristics from both parents as it has a mixture of chromosomes
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3
Q

Meiosis

A
  • Only occurs in reproductive organs
  • Produces four daughter cells
  • The process is repeated for a second time with all the phases
  • The end product is four haploid cells
  • All are gametes with one set of chromosomes
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4
Q

Meiosis and mitosis in reproduction

A
  • Mitosis is used in asexual reproduction

- Meiosis is used in sexual reproduction

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5
Q

Advantages of asexual reproduction

A
  • Produce a lot of offspring very quickly, the reproductive cycle is quicker
  • E.coli can divide every half an hour
  • This can allow organisms to colonise an area
  • Only one parent is needed
  • Can reproduce whenever conditions are favourable without waiting for a mate
  • Aphids reproduce in the summer when there is a lot of food
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6
Q

Disadvantages of asexual reproduction

A
  • No variation amongst genes in the population
  • If the environment changes and conditions become unfavourable, the whole population may become affected
  • Black Sigatoka is a disease that effects banana plants, it can be deadly as bananas reproduce asexually
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7
Q

Advantages of sexual reproduction

A
  • Creates genetic variation within the population, individuals have different characteristics
  • If conditions change, the population is likely to survive
  • This can lead to evolution and natural selection
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8
Q

Disadvantages of sexual reproduction

A
  • Takes more time and energy
  • Fewer offspring produced meaning fewer produced in a lifetime
  • Organisms need to attract mates
  • The population can not increase if individuals are isolated
  • Polar bears have to walk up to 100 miles to reproduce
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9
Q

DNA

A
  • Made up of nucleotides
  • Polymers made up of repeating nucleotides
  • Each nucleotide consists of a sugar phosphate base
  • The sugar and phosphate form a backbone to the structure
  • This forms a base to the double helix structure
  • The sugar and phosphate molecules alternate
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10
Q

The bases of DNA

A
  • A - Adenine
  • G - Guanine
  • T - Thymine
  • C - Cytosine
  • Bases are complementary that can only link to one another such as AT and GC
  • These bases are joined by hydrogen bonds
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11
Q

Storing of DNA

A
  • Stored as chromosomes and contains genes
  • Chromosomes are long coils of DNA
  • They are found in the nucleus of eukaryotic cells
  • A gene is a section of DNA that codes for a particular protein
  • All of an organisms DNA makes up its genome
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12
Q

How to extract DNA from a fruit

A
  • Mash up fruit and put them into a beaker containing laundry detergent and salt
  • The detergent will release the DNA is it breaks down cell membranes
  • The salt will make the DNA stick together
  • Filter the mixture to get the froth and big molecules out
  • Gently add some ice cold alohol to the mixture
  • The DNA will come out of the solutin as it is non-soluble in an ice cold solution. It will appear as a white precipitate
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13
Q

Proteins

A
  • Made by reading the code in the DNA
  • DNA controls the produciton of proteins in cells (protein synthesis)
  • Each protein has its own number and specific order of amino acids
  • The amino acid chains fold up to give each protein a different, spcific shape which will give them different functions
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14
Q

Genes

A
  • A section of DNA that codes for a particular protein is called a gene
  • The order of the bases in a gene decides the order of amino acids in a protein
  • Each amino acid is coded for by a sequence of three bases called a base triplet
  • The amino acids are joined together to make proteins, following the order of bases in that gene
  • Each gene contains a different sequence of bases to make proteins
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15
Q

Non-coding reigons in DNA

A
  • Many reigons in DNA do not code for any amino acids
  • Some of these reigons are still involved in protein synthesis
  • All of an organism’s DNA make up the genome
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16
Q

Mutations

A
  • A mutation is a rare, random change to an orgainsm’s DNA base sequence that can be imherited
  • If it happens in a gene, a genetic variant can be produced which is a different version of the gene
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17
Q

Genetic Variants

A
  • May code for a different sequence of amino acids, chamging the shape of the final protein and its activity
  • The activity of an enzyme may increase, decrease or stop all together
  • This could end up changing the characteristics of an organism
  • XDH is an enzyme. Fruit flies with XDH have red eyes, thise without it have brown eyes as they do not have enough for red eye pigment
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18
Q

Process of making proteins

A

1) Transcription

2) Translation

19
Q

Transcription

A
  • Proteins are made in the cell cytoplasm by subcelluar substances celled ribosomes. DNA is found in the cell nucleus. But it cant exit the nucleus due to due to it being too big
  • This is done using a molecule called messenger RNA (mRNA). Like DNA, mRNA is a polymer of nucleotide, but its shorter and only one string with uracil instead of thymine
20
Q

RNA Polymerase

A

The enzyme involved in joining together RNA nucleotides to make mRNA. This stage is called transcription

21
Q

Process of transcription

A

1) RNA Polymerase binds to a reigons of non-coding DNA in fromt of a gene
2) The two DNA strands unzip and the RNA moves along one of the strands of DNA
3) It uses the coding DNA in the gene as a template to make the mRNA. Base pairing between the DNA and RNA ensures that the mRNA is complementary to the gene
4) Once made, the mRNA molecule moves out of the nucleus it joins with the ribosome

22
Q

Process of translation

A

1) Amino acids are brought to the ribosome by another RNA molecule called transfer RNA (tRNA)
2) The order in which amino acids are brough to thr ribosome matches the base triplets in mRNA. Base triplets are also known as codons
3) Part of the tRNA’s structure is called an anitcodon. It is complementary to the codon for the amino acid. The pairing makes sure the amino acids in the correct order
4) Joined together by ribosome. This makes proteins

23
Q

Non-coding DNA in RNA Polymerase

A
  • Before any transcription, RNA polymerase has to bi d to reigon of non-coding DNA in front of a gene. If a mutation occurs in this reigon of DNA, the it could affect the ability of RNa polymerase to bind to it. It could be easier, it could be harder
  • How well RNA binds to this reigon of DNA will affect how much mRNA is transcribed and therefore how much protein is produced.
24
Q

Gregor Mendel

A
  • Austrian monk trained in mathematics and natural history. On his garden plot at the monastery, Mendel noted how characteristics in plants were passed on from one generation to the next
  • His results were published in 1866 and became the foundation of modern gentics
25
Q

Mendel and Pea Plants

A
  • One experiment, Mendel crossed two pea plants of different heights. The offspring produced were all tall pea plamts
  • He then bred two of the offspring, three tall were produced and one dwarf creating a 3:1 ratio
26
Q

What Mendel had proved

A
  • Height characteristics in pea plants were determined separately by inherited hereditary units passed on from each parent. The ratios of tall and dwarf plamts in the offspring produced showed that the unit for plants were dominant over small
27
Q

Mendel’ conclusion

A
  • Characteristics in plants are determined by hereditary units
  • Hereditary units are passed onto offspring unchaged from both parents, one unit from each parent
  • Hereditary units can be dominant or recessive
28
Q

Responses to Mendel’s work

A
  • Mendel’s work was new and unfamiliar to scientists of that time
  • Hereditary units turned out to be genes but at the time scientists did not have the background knowledge to properly undertsand Mendal
  • It was until Mendal died that people realise how important his work was as the mechanism of inheritance could be explained
29
Q

Background to Alleles

A
  • Different versions of the same gene
  • What genes you inherit, control your characteristics
  • Different genes control different characteristics. Some characteristics are controlled by a single gene but most are controlled by genes interacting
  • All genes exist in two versions called alleles which are represented by different letters by different letters in genetic diagrams
30
Q

Alleles

A
  • You have two alleles of every gene in your body - one on each chromosome in a pair
  • If an organism has two alleles for a particular gene that are the dame, then it is homozygous for that trait. If they are different, then it is heterozygous
31
Q

Dominant and recessive alleles

A
  • Some alleles are dominant and are represented with a capital letter. Dominant alleles will overrule recessive, this will be heterozygous
  • ## Both alleles must be recessive for it to be present
32
Q

Genotype

A

Combination of alleles that you have

33
Q

Phenotype

A

Your characteristics - different combinations of alleles give rise to different phenotypes

34
Q

Genetic diagrams

A
  • The inheritance of a single characteristic is calles a monohybrid inheritance. You can use a monohybrid cross to show how recessive and dominant traits for a single characteristic are inherited
  • Punnet squares are another method
35
Q

Carriers

A

People who have heterozygous genes, the recessive allele can be passed on to the offspring. If the other parent passes on a recessive allele, the characteristic will be present in the offspring

36
Q

Sex determination

A
  • There are 23 matched pairs of chromosomes in every human blood cell. The 23rd pair is labelled XX or XY, this determines wether you are male or female
  • Males must have an X and a Y chromosomes, the chromosome creates all male characteristics
  • Females have two X chromosomes. The XX combination causes female characteristics to develop
  • There is a 50/50 chance of either
37
Q

Sperm and Ova

A
  • Ovum always have an X chromosome
  • Sperm can carry either
  • The sperm determines the gender
38
Q

Examples of genetic diseases

A
  • Sickle cell amnaeia

- Cystic Fibrosis

39
Q

Family Pedigree

A

Family tree that shows presence of genetic disorders

40
Q

Sex-linked genetic characteristics

A
  • A characteristic is sex-linked if the allele that codes for it is located on a sex chromosome
  • The Y chromosome is smaller than the X chromosome and carries fewer genes
  • As men only have one X chromosome they often only have one allele for sex-linked genes
  • Because men only have one allele the characteristics of this allele show even if it is recessive. This makes men more likely to show recessive characteristics
  • Disorders caused by faulty alleles located on sex chromosomes arec alled sex-linked genetic disorders
41
Q

Colour Blindness

A
  • Caused by a faulty allele on the X chromosome
  • As its sex-linked, both the chromosome and the allele are written in the genetic diagram - X is the chromosome and n would be the allele
  • Women need two copies of the recessive alleles whilst men only need one making colour blindness more common in men
  • Women can therefore be carriers whilst men can not
42
Q

Haemophilia

A

Another example of a sex-linked characteristic on the X chromosome

43
Q

Blood Types

A
  • Humans have four potential blood types (A, B, AB, O)
  • The genes IA and IB are codominant, these means that by themseleves they will form blood grouos A and B, together they form AB
  • ## IO is recessive and for it to be the blood group, there needs to be two

Edexcel - Biology (9 decks)

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