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IGCSE Biology > Unit 5^ Variation + Selection > Flashcards

Unit 5^ Variation + Selection Flashcards

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1
Q

Where are chromosomes found?

A

Chromosomes are found in the NUCLEUS

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2
Q

What is a chromosome?

A

Long lengths of DNA 🧬 coiled up

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3
Q

How many chromosomes does each parent give?

A

Each parent (sperm+egg) give 23 chromosomes = durin fertilisation the genetic material fuses to form a cell w/ 46 chromosomes

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4
Q

How many chromosomes does a human have?

A

46 chromosomes

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5
Q

How many pairs of chromosomes are there in every human body cell?

A

23 pairs of chromosomes in every human body cell

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6
Q

What is a GENE

A

A gene is a short section of DNA which codes for a specific protein

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7
Q

What are different versions of the same gene called

A

An ALLELE = different versions of the same gene

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8
Q

What are the 4 nitrogenous bases in DNA

A

ADENINE + THYMINE

CYTOSINE + GUANINE

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9
Q

What does RNA polymerase do?

A

It’s an ENZYME involved in joinin up the base sequence to make mRNA

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10
Q

Describe a DNA 🧬 molecule

A

two strands coiled to form a double helix linked by a series of paired bases : adenine + thymine, guanine +cytosine

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11
Q

Give 3 differences between a DNA molecule and an RNA molecule

A
  • DNA is double helix, whereas RNA is single stranded
  • DNA has the sugar deoxyribose, whereas RNA has RIBOSE
  • RNA contains base URACIL (U) instead of thymine (T) which is in dna
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12
Q

What’s an allele

A

Different version of the same gene

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13
Q

How many copies of each gene do humans have?

A

2 copies

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14
Q

What is meant by the term HOMOZYGOUS

A

When an individual has two alleles the same (TT)

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15
Q

What is meant by the term HETEROZYGOUS

A

When an individual has two different alleles (Tt)

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16
Q

Genotype

A

The combination of alleles for a certain characteristic

Can be either homozygous or heterozygous

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17
Q

Phenotype

A

The observable characteristics resulting from the genotype

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18
Q

What is meant by the term polygenic inheritance

A

Characteristics controlled by 2 or more genes working together

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19
Q

Codominance

A

A pattern of inheritance where

neither allele of a gene is dominant over the other

so that both alleles are expressed in the phenotype

🌺🌼===>🌸

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20
Q

What is a pedigree

A

A family tree of genetic disorders

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21
Q

Describe what is meant by the term cytokinesis

A

In mitosis, when after telophase the cytoplasm splits into two genetically identical daughter cells

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22
Q

What is a mutation

A

A random change in genetic code

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23
Q

What is meant by the term mutagen

A

Factors that increase the rate of mutation

E.g. carcinogens present in cigarette smoke or gamma radiation

24
Q

What is meant by the term ‘selective breeding’

A

When organisms are selectively bred to develop desirable features

25
Q

Name the 4 steps in the process of selective breeding

A

🐮 select organisms with desirable characteristics

🐮 breed them w each other

🐮 select best ‘offspring’

🐮 repeat……

26
Q

Explain why selective breeding is not natural selection

A

Because in selective breeding the selection pressure is not environmental, it is just human desire

27
Q

Explain the theory of evolution

A

Evolution = life began as simple organisms which evolved as a result of random mutations to more complex organism over time

28
Q

Describe the 5 steps in NATURAL SELECTION

A

🌱 organisms in a species show variation in characteristics as a result of random mutations

🌱there’s competition for limited resources in the environment

🌱the organism w most suitable characteristics for the environment has best chance of survival

🌱the ‘fittest’ has the best chance of breeding + passing on its genes

🌱over generations the characteristic which increases survival becomes more common + as a result the species becomes better adapted for its enviro

29
Q

What organism is it the best to see natural selection take place in and why?

A

BACTERIA or INSECTS

because they reproduce very quickly unlike animals

30
Q

What do mutations produce

A

Random change in sequence of bases= genetic variant

31
Q

What does a DNA codon code for

A

The sequence codes for an amino acid

32
Q

What can mutations do to enzymes?

A

Mutations can cause the very specific active site to change shape, altering the enzymes function

33
Q

Why do some mutations not take effect on the phenotype

A

The mutations don’t effect the phenotype SOMETIMES because the mutation has occurred in an unimportant region of DNA or the mutated codon still codes for the same protein

34
Q

What is meant by the term ‘antibiotic’

A

Chemicals that kill/ reduce growth of microorganism

BUT DONT WORK ON VIRUSES cos viruses use a host to reproduce

35
Q

Describe how bacteria become resistant to an antibiotic (4 marks)

A

Bacteria contains a random mutation in its DNA which gives it resistance to a particular antibiotic

This resistance means it’s better able to survive + reproduce = lots of bacteria inherit resistance to that antibiotic

Bacteria reproduce fast, so resistance is prominent quickly!

Resistant bacteria r no longer effected by antibiotic= antibiotic ineffective

36
Q

What is a NUCLEOTIDE and what is it made up of

A

A nucleotide is a DNA monomer and it is made up of
• a phosphate group
• sugar molecule (deoxyribose)
• a nitrogenous base (A,T,C or G)

37
Q

Explain the process of DNA replication 🧬 🧬🧬🧬🧬🧬🧬🧬🧬🧬🧬

A

Before a cell is about to divide it must replicate each DNA molecule in the nucleus.

  • the polynucleotide strands separate
  • each strand acts as a template for an new strand of DNA
  • DNA polymerase (enzyme which joins base pairs) puts nucleotides into pairs
  • now 2 identical DNA molecules r formed
38
Q

All genes code for ________

A

All genes code for PROTEINS

39
Q

What is a codon

A

A triplet code which codes for an amino acid

40
Q

Sequences of codons for all amino acids in a protein is a _____

A

Sequences of codons for all amino acids in a proteins is a GENE

41
Q

What is protein synthesis

A

The making of proteins in 2 stages

42
Q

What are the 2 types of RNA and what is there function

A

mRNA (Messenger RNA)
= forms a copy of the DNA code

tRNA (Transfer RNA)
= which carries amino acids to the ribosomes to make the protein

43
Q

Describe the process of protein synthesis referencing the 2 main stages and the role of mRNA + tRNA

A

🔮TRANSCRIPTION [in the nucleus]
Proteins r made by ribosomes in cytoplasm but DNA molecules found in nucleus r too big to move out=
•so the DNA info needs to be carried out of nucleus into the ribosomes in the cytoplasm
🔮mRNA carries this info by unzipping the DNA strand, reading it using enzyme(RNA polymerase) + lining up complimentary base pairs (U instead of T tho)

💬TRANSLATION [in the cytoplasm]
Now the mRNA template needs to be decided into a particular protein.
•so the mRNA binds to a ribosome
💬now the tRNA brings amino acids to the ribosome // these amino acids have anticodons which r complimentary to the codon on the template strand
💬each tRNA bonds to a matching mRNA
• which forms an amino acid, it’s repeated until it’s a chain = a PROTEIN= a GENE

44
Q

Give 3 reasons for selectively breeding animals

A

🐄 produce more meat, eggs or milk

🐖 produce more offspring

🐏 to be resistant to certain diseases

45
Q

Give 3 reasons for selectively breeding crops

A

🌵 resistant to harsh weather

🌴 give higher yields

🌲have a better balance of nutrients (PROtato)

46
Q

What is artificial insemination

A

Instead of physically breeding animals together… semen w desirable features is kept + stored and injected into the uterus of a cow w a syringe

47
Q

Give 2 benefits of Artificial Insemination

A

🐄🐂 it can be stored + used even after cow dies

🐂🐄 semen from one cow can fertilise many thousands of cows

48
Q

Explain how animals are CLONED 🐑

A

Scientists took an ovum (egg cell) + removed its nucleus = ENUCLEATED CELL 🥚

Took cells from mammary gland + cultured in a solution (this mammary gland is the gene we’re copying) 🥛

They then took the mammary gland cell and fused it w the enucleated cell using electric current ⚡️⚡️

They then planted the embryo into uterus of a surrogate sheep 🐑 == dolly born, genetically indentical

49
Q

What is meant by the term diploid

A

Diploid number of chromosomes = 46

50
Q

What is meant by the term haploid

A

Haploid numbers of chromosomes = 23

51
Q

What is INTERPHASE and when does it happen in both mitosis+ meiosis

A

Interphase is right before cell division when DNA replicates

52
Q

Give 3 genetic factors that cause variation in genes (genes control inherited traits)

A
  • Eye/hair colour
  • blood group
  • inherited disorders
53
Q

Give 3 environmental factor that cause variation in genes

A
  • smoking (lung cancer)
  • poor diet (stunted growth)
  • exposure to excess UV (melanoma)
54
Q

Recessive

A

Allele that is not expressed in the phenotype when a dominant allele (of the gene) is present

55
Q

Dominant

A

Allele of the gene that is expressed in the phenotype

56
Q

What is a genome?

A

The entire DNA of an organism

IGCSE Biology (6 decks)

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