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GCSE Biology > B12 Reproduction > Flashcards

B12 Reproduction Flashcards

1
Q

What does DNA stand for?

A
  • Deoxyribonucleic acid
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2
Q

What is DNA?

A
  • Chemical that all of the genetic material in a cell is made from
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3
Q

What does DNA contain?

A
  • Coded information (all the instructions to put an organism together & make it work)
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4
Q

What determines inherited characteristics?

A
  • What’s in your DNA
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5
Q

Where is DNA found?

A
  • In the nucleus of animal & plant cells
  • In long structures called chromosomes
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6
Q

What do chromosomes come in?

A
  • Pairs
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7
Q

What is the structure of DNA?

A
  • Polymer
  • Made of two strands coiled together in the shape of a double helix
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8
Q

What is a gene?

A
  • A small section of DNA found on a chromosome
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9
Q

What does each gene code for (tell the cells to make)?

A
  • Particular sequence of amino acids which are put together to make a specific protein
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10
Q

How many amino acids are used to make proteins?

A
  • 20
  • However makes up thousands of different proteins
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11
Q

What does DNA determine?

A
  • What proteins the cell produces, e.g. haemoglobin, keratin
  • In turn determines what type of cell it is e.g. red blood cell, skin cell
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12
Q

What is a genome?

A
  • Entire set of genetic material in an organism
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13
Q

What have scientists discovered about genes?

A
  • Scientists have worked out the complete human genome
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14
Q

Why is understanding the human genome to identify genes important for science & medicine?

A
  • It allows scientists to identify genes in the genome that are linked to different types of disease
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15
Q

Why is understanding the human genome to know genes linked to inherited diseases important to science & medicine?

A
  • Knowing which genes are linked to inherited diseases could help us to understand them better & could help us to develop effective treatments for them
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16
Q

Why is understanding the human genome to trace migration important to science & medicine?

A
  • Scientists can look at genomes to trace the migration of certain populations of people around the world
  • All modern humans are descended from a common ancestor who lived in Africa, but humans can now be found all over the planet
  • Human genome mostly identical in all individuals, but as different populations of people migrated away from Africa, they gradually developed tiny differences in their genomes
  • By investigating these differences, scientists can work out when new populations split off in a different direction & what route they took
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17
Q

What does sexual reproduction produce?

A
  • Genetically different cells
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18
Q

What is sexual reproduction?

A
  • Where genetic information from two organisms (father & mother) is combined to produce offspring which are genetically different to either parent
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19
Q

What happens in sexual reproduction?

A
  • Mother & father produce gametes by meiosis e.g. egg & sperm cells in animals
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20
Q

In humans, how many chromosomes does each gamete contain?

A
  • 23 chromosomes
  • Half the number of chromosomes in a normal cell
  • Instead of having two of each chromosome, a gamete has just one of each
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21
Q

How is the full cell formed?

A
  • The egg (from the mother) & the sperm cell (from the father) fuse together (fertilisation) to form a cell with the full number of chromosomes (half from the father, half from the mother)
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22
Q

What does sexual reproduction involve?

A
  • Fusion of male & female gametes
  • Because there are two parents, the offspring contain a mixture of their parents’ genes
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23
Q

Define gamete

A

Sex cell

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24
Q

Why does the offspring inherit features from both parents?

A
  • It’s received a mixture of chromosomes from its mum and its dad (and it’s the chromosomes that decide how you turn out)
  • This mixture of genetic information produces variation in the offspring
  • Flowering plants can reproduce this way too; they also have egg cells, but their version of sperm is pollen
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25
Q

What does asexual reproduction produce?

A
  • Genetically identical cells
26
Q

Who are the parents in asexual reproduction?

A
  • One parent so the offspring are genetically identical to that parent
27
Q

How does asexual reproduction occur?

A
  • Mitosis (an ordinary cell makes a new cell by dividing in two)
  • Therefore the new cell has exactly the same genetic information (i.e. genes) as the parent cell - it’s called a clone
28
Q

Why is there no variation in asexual reproduction?

A
  • no fusion of gametes
  • no mixing of chromosomes
  • no genetic variation between parent and offspring
29
Q

What organisms produce asexually?

A
  • Bacteria
  • Some plants
  • Some animals
30
Q

What happens when gamete fusion takes place?

A
  • Gametes only have one copy of each chromosome, so that when gamete fusion takes place, you get the right amount of chromosomes again (two copies of each)
31
Q

What does meiosis produce?

A
  • Cells with half the normal number of chromosomes
32
Q

Describe the first step of meiosis

A
  • Before cell division, cell duplicates its genetic information, forming two armed chromosomes - one arm of each chromosome is an exact copy of the other arm.
  • After replication, the chromosomes arrange themselves into pairs
33
Q

Describe the second step of meiosis

A
  • In the first division in meiosis the chromosome pairs line up in the centre of the cell
34
Q

Describe the third step of meiosis

A
  • The pairs are then pulled apart so each new cell only has one copy of each chromosome
  • Some of the father’s chromosomes & some of the mothers chromosomes go into each new cell
35
Q

Describe the fourth step of meiosis

A
  • In the second division, the chromosomes line up again in the centre of the cell
  • Arms of chromosomes are pulled apart
36
Q

Describe the final step of meiosis

A
  • You get four gametes, each w/ only a single set of chromosomes in it
  • Each of the gametes is genetically different from the other because the chromosomes all get shuffled up during meiosis & each gamete only gets half of them, at random
37
Q

What happens to the cell produced by gamete fusion?

A
  • Replicates itself
38
Q

What happens after two gametes have fused after fertilisation?

A
  • Resulting new cell divides by mitosis to make a copy of itself
  • Mitosis repeats many times to produce lots of new cells in an embryo
  • As the embryo develops, these cells then start to differentiate into the different types of specialised cell that make up a whole organism
39
Q

What do your chromosomes control?

A
  • Whether you’re male or female
40
Q

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

A
  • 23
41
Q

What chromosomes define sex?

A
  • Of the 23 pairs, 22 are matched pairs of chromosomes that just control characteristics
  • The 23rd pair are labelled XY or XX. They’re the two chromosomes that decide your sex - whether you turn out male or female
42
Q

What chromosomes do males have?

A
  • Males have an X & a Y chromosome: XY
  • The Y chromosome causes male characteristics
43
Q

What chromosomes do females have?

A
  • Females have two X chromosomes: XX
  • The XX combination allows female characteristics to develop
44
Q

How is sex decided during fertilisation?

A
  • When making sperm, the X & Y chromosomes are drawn apart in the first division in meiosis
  • There’s a 50% chance of each sperm cell gets an X-chromosome & 50% chance it gets a Y-chromosome
  • A similar thing happens when making eggs, but the original cell has two X-chromosomes, so all the eggs have one X-chromosome
45
Q

What controls the characteristics you develop?

A
  • What genes you inherit
46
Q

What do different genes control?

A
  • Different characteristics
  • Some characteristics are controlled by a single gene e.g. mouse fur colour & red-green colour blindness in humans
  • However, most characteristics are controlled by several genes interacting
47
Q

How do genes exist?

A
  • In different versions called alleles (which are represented by letters in genetic diagrams)
48
Q

How do we know that an organism is homozygous for a trait?

A
  • If an organism has two alleles for a particular gene that are the same
49
Q

How do we know that an organism is heterozygous for a trait?

A
  • If the organisms alleles for a particular gene are different
50
Q

How much of every gene do you have in your body?

A
  • Two versions (alleles)
  • One of each chromosome in a pair
51
Q

What is the relationship between genotype & phenotype?

A
  • Your genotype is the combination of alleles that you have
  • Your alleles work at a molecular level to determine what characteristics you have - your phenotype
52
Q

What is cystic fibrosis caused by?

A
  • a Recessive Allele
53
Q

What is cystic fibrosis?

A
  • a genetic disorder of the cell membranes
54
Q

What does cystic fibrosis result in?

A
  • Body producing thick sticky mucus in the air passages & pancreas
55
Q

What is polydactyly caused by?

A
  • a dominant allele
56
Q

What is polydactyly?

A
  • a genetic disorder where a baby’s born w/ extra fingers or toes
57
Q

What can embryos be screened for?

A
  • Genetic disorder
58
Q

Describe embryonic screening

A
  • During IVF, embryos are fertilised in a lab, and then implanted into the mother’s womb
  • Before being implanted, it’s possible to remove a cell from an embryo & analyse its genes
  • Many genetic disorders can be detected in this way, such as cystic fibrosis
  • It’s also possible to get DNA from an embryo in the womb & test that for disorders
59
Q

Why is embryonic screening controversial?

A
  • There are a lot of social, economic and ethical concerns surrounding embryonic screening
  • Controversial because of the decisions it could lead to
  • For embryos produced by IVF, after screening, embryos w/ ‘bad’ alleles would be destroyed
  • For embryos in the womb - screening could lead to the decision to terminate the pregnancy
60
Q

What are some arguments against embryonic screening?

A
  • It implies that people with genetic problems are ‘undesirable’ - this could increase prejudice
  • There may come a point where everyone wants to screen their embryos so they can pick the most ‘desirable’ one e.g. they want a blue-eyed, blond-haired, intelligent boy
  • Screening is expensive
61
Q

What are some arguments for genetic screening?

A
  • It will help to stop people from suffering
  • Treating disorders costs the Government (and the taxpayers) a lot of money
  • There are laws to stop it going too far. At the moment parents cannot even select the sex of their baby (unless it’s for health reasons)

GCSE Biology (4 decks)

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