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GCSE Biology > B13 Genetics and Reproduction > Flashcards

B13 Genetics and Reproduction Flashcards

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1
Q

What is Asexual Reproduction?

A
  • Only involves one parent
  • Cells divide by mitosis
  • no joining of gametes (sex cells), no mixing genetic information, NO VARIATION IN OFFSPRING= genetically identical offspring (clones)
  • common in small animals + plants, fungi, bacteria
  • body cells-> growth, replace worn out tissue
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2
Q

What is Sexual Reproduction?

A
  • male sex cell and female sex cell (gametes/parents cells fuse) fuse to form zygote-> forms genetically varying offspring
  • gametes form through meiosis
  • inherit genetic information from both parents
  • more variation in offspring than asexual reproduction

Plants gametes= egg cells, pollen
Animals= egg cells (ova), sperm

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3
Q

Why is Sexual Reproduction risky and good?

A
  • relies on 2 sex cells, often from 2 individuals, meeting and fusing
  • BUT introduces variation= key to long term survival of a species
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4
Q

Where does Meiosis take place?

A

In the reproductive organs of animals and plants

  • humans= ovaries and testes
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5
Q

What is the process of Meiosis?

A

only takes place in reproductive organs

  • all chromosomes in the cell are copied
  • the genetic material moves to the edges of the cell and divides into two
  • the genetic material moves to the edges of the cell again
  • the cell divides one more time (forming 4 genetically varying gametes-> half the number of chromosomes in a normal cell)
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6
Q

How many chromosomes are there in a cell?

A

23 pairs

1 from mother= maternal chromosomes

1 from father= paternal chromosomes

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7
Q

What is a Haploid?

A

a cell that only has half the amount of normal genetic material
ie gametes (23 single chromosomes)

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8
Q

What happens in Fertilisation?

A
  • 2 sex cells join, forming a single new cell with a full set of chromosomes
  • unique cell, begins dividing rapidly by mitosis
  • cells differentiate as embryo develops (tissues, organs, organ systems)
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9
Q

What is the difference between Asexual and Sexual reproduction?

A

Asexual
- offspring produces from mitosis of parent cells
- same chromosomes, same genes
- no variation in genetic material

Sexual
- gametes produces by meiosis in sex organs of parents
- variation: each gamete is different
- gametes fuse, more variation

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10
Q

What are the advantages and disadvantages of Asexual Reproduction?

A
  • only 1 parent, less time and energy wasted finding a mate/spreading gametes
  • faster than sexual reproduction
  • environmental changes can cause species to die out (lack of variation, cannot adapt
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11
Q

What are the advantages and disadvantages of Sexual Reproduction?

A
  • produces varying offspring, survival advantage if environment changes (natural selection)
  • 2 parents/ gametes are needed-> time and energy to find mate/spread gametes
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12
Q

How does Fungi usually reproduce?

A

Asexual
- toadstool, puffballs= asexual fruiting bodies full of spores
- mould= reproduce asexually

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13
Q

Why and how do Fungi reproduce sexually?

A
  • when conditions aren’t good ie dry
  • 2 hyphae from different fungi join, nuclei fuse, hypha has 2 sets of chromosomes
  • meiosis, haploid spores, may produce fungi better adapted to changing conditions
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14
Q

How do plants reproduce?

A

Sexually- pollen and egg cells (gametes)

  • pollen reaches egg cell of another plant= pollination (Insects, birds)
  • pollen fuses with egg cells, seeds are formed
  • variation, plants survive in changing conditions (natural selection)
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15
Q

How can some plants reproduce asexually?

A

specially directed mitosis
- tiny new plants form on runner stems (strawberry plants, spider plants)

neg= new plants are identical to parents, no variation
pos= new plants formed even if flowers are destroyed (frost, eaten etc)

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16
Q

How do the parasites that cause malaria reproduce?

A

Both Asexually and Sexually

Asexually= in human host
Sexually= in mosquitos
the mosquito takes blood meal, temp drops between human body, mosquito triggers Sexual reproduction in parasites in red blood cells
- sexual forms develop, burst out of blood cells, meet + form zygotes
- zygotes undergo meiosis, produce new asexual parasites, infect new human host

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17
Q

What does DNA stand for?

A

Deoxyribonucleic acid

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18
Q

What is DNA?

A

A polymer made up of many repeating units

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19
Q

What are chromosomes made of?

A

Long molecules of DNA

  • in long strands of DNA twist and spiral, form double helix structure
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20
Q

What are genes?

A

small sections of DNA where genetic information (determining inherited characteristics) is stored

  • each gene codes for a specific sequence of amino acids-> make specific protein
  • genes control proteins, proteins control make up of specialised cells that form tissues, tissues form organs, organs systems make up whole body
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21
Q

What is the genome of an organism?

A

The entire genetic material of an organism

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22
Q

What is the Human Genome Project?

A

a project that sequences the entire human genome

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23
Q

How does the Human Genome code for so many proteins?

A

it uses the same gene in different ways or switches part of a gene on and off

24
Q

Why is sequencing genomes
important?

A
  • importance in medicine
  • work out relationships between different types of organisms
  • can identify causes of disease, help choose right treatment
25
Q

Why is understanding the human genome important?

A
  • understand inherited disorders (cystic fibrosis)
  • understand genes linked to specific types of diseases (type 2 diabetes, cancer)
  • track human migration, evolution
26
Q

Where is DNA found?

A

In the nucleus of cells

27
Q

What is a nucleotide?

A

the combination of a sugar, phosphate and base

28
Q

What are the 4 letters of bases?

A

AT
CG

29
Q

What is a DNA polymer made up of?

A

repeating nucleotide units

30
Q

How many bases code for 1 amino acid?

A

3

31
Q

How many bases are in a gene?

A

hundreds or thousands

32
Q

What does the order of bases control?

A

Which amino acids are assembled to produce a specific protein in the body cells

33
Q

What does a gene code for?

A
  • a particular combination of amino acids, making up a specific protein
34
Q

Why are complementary strands (AT, CG) in DNA important

A
  • Holds the double helix structure together
  • Important for information from genes on the DNA to be translated into proteins in the cells
35
Q

What is the process of Protein synthesis?

A
  • genes produce template for protein, reflecting sequence of bases in the DNA + small enough to leave nucleus through nuclear membrane
  • leaves nucleus + binds to ribosome
  • cytoplasm contains carrier molecules each attached to specific amino acid
  • carrier molecules attach to template in order given by DNA
  • amino acids join to form specific protein
  • protein detaches from carrier molecules, molecules detach from template + return to cytoplasm to pick up more amino acids
36
Q

What are uses for proteins produced from protein synthesis?

A

Enzyme- fold to produce an active site
Structural protein- form fibrous structures like collagen
Hormone/Muscle/Part of cell membrane structure- fold to carry out specific job in cell

37
Q

When is a gene expressed?

A

When a gene codes for a protein that is synthesised in the cell

38
Q

What are uses for non-coding parts of the DNA?

A

Switching genes/parts of genes on and off

  • variation in non coding parts can affect how genes are expressed -> affects phenotype
39
Q

What is a Phenotype?

A

The physical appearance of biochemistry of an organism

40
Q

What are mutations?

A

new forms of genes resulting from changes in existing genes

  • often occur in mistakes made in copying DNA
41
Q

What are effects of mutations on proteins made?

A
  • most don’t alter protein formed, but can alter appearance but not function
  • can code for change in amino acids, cause altered protein that folds to give a different shape-> active site may no longer fit substance OR structural protein loses strength
  • can give advantage (eg produce more efficient enzyme OR stronger structural protein)
42
Q

How can mutations in Non-coding DNA affect the phenotype?

A
  • doesn’t directly affect the phenotype

HOWEVER
- variants in non coding DNA: affects which genes are switched on and off, changing genes expressed-> effect phenotype

43
Q

What is an allele?

A

A variant/different form of gene that each code for a different protein

  • combination of alleles inherited determines characteristics
    (genes= chromosomes that carry genetic information)
44
Q

What is a Homozygote?

A

an individual with 2 identical alleles for a characteristic

BB, bb

45
Q

What is a Heterozygote?

A

An individual with different alleles for a characteristic

Bb

46
Q

What is a Genotype?

A

The genetic makeup of an individual regarding a particular characteristic

Bb, bb etc

47
Q

What is a Phenotype?

A

The physical appearance of an individual regarding a particular characteristic

Black fur or Brown fur in mice

48
Q

What is the difference between a Dominant allele and a Recessive allele?

A

Dominant= always expressed in the phenotype, even if only 1 copy is present

Recessive= only expressed if 2 copies are present

49
Q

What are sex chromosomes?

A

1 pair of chromosomes out of 23 that differ, determining the sex of offspring
Female (human)= XX
Male (human)= XY

50
Q

What are inherited disorders?

A

disorders result of change in bases or coding of our genes, passed from parent to child

51
Q

What is Polydactyly?

A

babies born with extra fingers/toes
- usually caused by dominant allele

  • if it is a heterozygous gene, there is a 50% chance of passing it to children
  • if it is a homozygous gene, there is a 100% chance of passing it to children
52
Q

What is Cystic Fibrosis?

A

Genetic disorder, affecting lungs, digestive system and reproductive system. Treatment includes physiotherapy, antibiotics to keep lungs clear of mucus + infection, no cure

  • caused by recessive phenotype
  • has to be inherited from both parents
53
Q

What is a carrier?

A

When a parent carries a recessive unhealthy allele but have a dominant healthy allele, so have no symptoms but can pass the disease to their children

54
Q

How can people screen for genetic disorders?

A
  • use genetic tests to show people if they are a carrier of a faulty gene
  • screen pregnancies (embryos and fetuses) for alleles that cause inherited disorders
  • embryos can be screened before implantation during IVF
  • useful tests, raise ethical concerns
55
Q

How can you screen embryos?

A
  • harvest cells from developing individual

Amniocentesis:
- 15-16 weeks of pregnancy
- taking amniotic fluid from around fetus. Contains fetal cells, used for genetic screening

Chorionic villus sampling:
- 10-12 weeks of pregnancy
- taking small sample of tissue from placenta, provides fetal cells to screen

56
Q

What are the disadvantages of screening embryos?

A
  • associated risk of miscarriage, distressing for parents
  • can give false pos/neg results-> termination of healthy baby, unexpected birth of child with genetic disorder
  • leaves decision of terminating baby (hard decision)
  • expensive process
  • could give rise in demand to ‘designer babies’-> parents used screening to choose children with desirable characteristics (looks, sex, intelligence)
57
Q

What happens if screening shows an embryo is affected by genetic disorders?

A

Parents can choose between keeping the baby with a genetic disorder or have an abortion/not proceed with implantation (IVF)

GCSE Biology (20 decks)

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