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How is inheritance explained? Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is a gene?

A
  • section of DNA that carries the code to make a protein. Our genes are what form the basis of inheritance, and can be found at specific locations on our chromosomes (gene loci).
  • a particular section of DNA that codes for the creation of an individual polypeptide chain (which makes up a protein)
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2
Q

What is DNA?

A

Deoxyribonucleic acid (DNA) sits inside the nucleus of your cells and is formed by the continuous pairing of base pairs into a longer, double-stranded nucleic acid chain

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3
Q

What is nucleic acid?

A

the class of macromolecules that includes DNA and RNA. All nucleic acids are polymers made out of nucleotide monomers

large biomolecule that hold genetic information

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4
Q

What is a nucleotide?

A

base pairs are part of individual nucleic acid molecules known as nucleotide monomers, each of which consists of the same basic structure

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5
Q

What makes up a nucleotide monomer?

A
  • a phosphate group
  • a deoxyribose sugar
  • a nitrogen-containing base, which can be one of four varieties
    − adenine (A)
    − thymine (T)
    − guanine (G)
    − cytosine (C)
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6
Q

What is the function of a gene?

A

It acts like a set of instructions which a cell will then read to create the important protein molecules needed for a range of cellular functions, such as growth and regeneration. The order of bases in the double helix determines which protein gets made. For instance, the sequence ‘ATG’ will send different instructions than the sequence ‘GGG’.

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7
Q

What is a genome?

A
  • the complete set of DNA contained within an organism’s chromosomes
  • haploid set of chromosomes within an organism, including all of its genes. A copy of the entire genome is contained in all cells within the body that have a nucleus.
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8
Q

What is an allele?

A

alternate forms of a gene
different forms of the same gene but with small differences in their base sequence.
found at the same gene locus on corresponding chromosomes.

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9
Q

What is a locus?

A

the fixed position on a chromosome where a particular gene is located

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10
Q

What is inheritance?

A

the genetic transmission of traits from parent to offspring

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11
Q

What is a phenotype?

A

the observable trait of an individual

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12
Q

What does haploid mean?

A

describes a single set of chromosomes (n)

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13
Q

How many alleles are present at a gene locus?

A

only two alleles are present at the gene locus of any one individual, each of which is inherited from one parent – one from mom and one from dad.

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14
Q

How is the genome measured?

A

measured by the number of base pairs contained in a haploid set of chromosomes. For example, the human genome is around three billion base pairs in length (haploid), which equates to roughly 25 000 different genes.

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15
Q

What is a histone protein?

A

highly basic proteins that associate with DNA inside the nucleus and help it condense into a chromosome allowing it to fit inside the nucleus

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16
Q

What is a chromosome?

A

each molecule of DNA is coiled tightly around histone proteins and packaged into thread-like structures called chromosomes. Human somatic cells mostly contain 46 chromosomes and therefore have a diploid number of 2n = 46.
the structure made of protein and nucleic acids that carries genetic information

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17
Q

What influences the size of a chromosome?

A

the number of nucleotides they contain

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18
Q

What is a somatic cell?

A

any cell that is not a reproductive cell (such as sperm and egg cells). Somatic cells are diploid (2n), meaning they contain two sets of chromosomes – one inherited from each parent

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19
Q

What is a chromatid?

A

one half of a replicated chromosome. Prior to cell division, chromosomes are duplicated and two copies join together at their centromeres (joined chromatids are known as sister chromatids)

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20
Q

What are telomeres?

A

A region of repetitive base sequences that is found at the end of every chromosome. It is used to protect the ends of chromosomes from fusing with other nearby chromosomes in the nucleus.

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21
Q

What is a DNA molecule?

A

Each chromosome is composed of a long DNA molecule that has been coiled tightly around histone proteins.

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22
Q

What is a centromere?

A

A specialised sequence of DNA that holds together the two chromatids. It is very important for the process of meiosis

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23
Q

What are sister chromatids?

A

The identical daughter strands of a replicated chromosome.

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24
Q

What is the short arm?

A

Also known as the ‘p arm’ – this is the section of the chromosome that is shorter in length.

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25
Q

What is the long arm?

A

Also known as the ‘q arm’ – this is the section of the chromosome that is longer in length.

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26
Q

What are homologous chromosomes?

A

a pair of chromosomes of similar length, gene position, and centromere location. One of the pair is inherited from the mother (maternal chromosome) and the other from the father (paternal chromosome)
These sets of chromosomes, while not identical in base sequence, are paired and identified together as they contain the same genes.

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27
Q

What are the criteria for homologous chromosomes?

A

1 they are the same in size and length
2 they have the same centromere position
3 they share the same genes at the same gene loci.

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28
Q

Do genes align on homologous chromosomes?

A

each gene shares the same locus on each of the two homologues, allowing scientists to identify the exact location and base sequence for each gene of our genome

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29
Q

What is a karyotype?

A

a visual representation of an individual’s entire genome organised into homologous pairs

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30
Q

Why are karyotypes important?

A

to check for possible genetic abnormalities. When reading karyotypes, scientists will check that the correct number of chromosomes are present and that the size and length of each chromosome are correct.

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31
Q

What is an autosome?

A

any chromosome (1–22) in humans that is not a sex chromosome

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32
Q

What is a sex chromosome?

A

a chromosome responsible for determining the biological sex of an organism.
In humans, sex chromosomes can be either an X or Y chromosome

33
Q

What is aneuploidy?

A

when a cell or organism varies in the usual number of chromosomes in its genome by the addition or loss of a chromosome
refers to a chromosomal abnormality in which an organism possesses an incorrect number of total chromosomes caused by the addition or loss of an individual chromosome. In humans, this would mean having more or less than the usual number of 46.
Depending on how many chromosomes are affected, we have different names to describe varying forms of aneuploidy. For instance:
* if an organism has one missing chromosome (2n-1), we call this monosomy.
* if an organism has one extra chromosome (2n+1), we call this trisomy.
* if an organism has two extra chromosomes (2n+2), we call this tetrasomy.

34
Q

What is polyploidy?

A

when an organism contains additional sets of chromosomes in its genome
chromosomal abnormality in which an organism has more than two sets of each chromosome. In humans, this would mean that rather than being diploid
(2n = 46), the individual would be 3n = 72 or more.

35
Q

What is monosomy?

A

a genetic abnormality where an organism has one missing chromosome
Turner syndrome (one X)

36
Q

What is trisomy?

A

a genetic abnormality where an organism has one extra chromosome
Down syndrome (extra copy of 21)

37
Q

What is tetrasomy?

A

a genetic abnormality where an organism has two
extra chromosomes
Tetrasomy X (XXXX)

38
Q

What is the effect of polyploidy?

A

Polyploidy is typically lethal in humans, meaning that it is extremely rare for a foetus to survive to term. However, it is quite common for other organisms, especially plants, to thrive with additional sets of chromosomes. For example, one advantage of polyploidy includes increased size and hardiness in certain types of fruit. Even farmed Atlantic salmon are triploid. This makes the fish sterile, and also leads to a faster growth rate.

39
Q

What is a summary of genetics?

A

A gene is the basic unit responsible for the process of inheritance from one generation to the next. These genes, each composed of unique sequences of DNA, can be found at specific gene loci along a chromosome, which themselves pair together inside the nucleus of a cell to form homologous pairs. With this knowledge, scientists are able to karyotype the entire human genome in an attempt to identify and uncover genetic abnormalities in humans.

40
Q

What is meiosis?

A

Meiosis is a specialised form of cell division that occurs in sexually reproducing organisms and is used to produce the gametes necessary for sexual reproduction.

41
Q

What is a zygote?

A

the diploid cell formed by the combination of two haploid gamete cells

42
Q

What is a gamete?

A

reproductive cells that arise from germline cells and contain half the genetic material (n) of a somatic cell. The gametes in animals are sperm and egg cells

43
Q

What is a germline cell?

A

cells that are involved in the generation of gametes in eukaryotes

44
Q

What is a gonad?

A

the organs that produce gametes from germline cells.
In humans these are the testes (male) and ovaries (female)

45
Q

What are the two distinct cellular divisions in meiosis?

A

The process involves two distinct cellular divisions:
* meiosis I – which separates each homologous chromosome into two different cells.
* meiosis II – which separates each sister chromatid into four different cells.

46
Q

What happens in prophase 1?

A

The nuclear membrane breaks down as chromosomes condense and line up in homologous pairs. This is important for crossing over of genetic material between the homologues

47
Q

What happens in metaphase 1?

A

Homologous chromosomes will then line up randomly on opposite sides of the metaphase plate, with one copy (paternal or maternal) on either side. Each chromosome is then attached to the microtubules of whichever pole it is closest to in preparation to be separated during the next stage.

48
Q

What is a metaphase plate?

A

the equator of a dividing cell where chromosomes will line up during metaphase

49
Q

What are microtubules?

A

long tube-like fibre proteins that form part of the cytoskeleton of a eukaryotic cell and help give the cell its structure. Microtubules are used for a variety of cell movements, including transport of cell organelles and the movement of chromosomes during cell division

50
Q

What is independent assortment?

A

The random orientation of homologous chromosomes along the metaphase plate during metaphase I. Each pair of homologues line up randomly, irrespective of the orientation of other homologous pairs.

51
Q

What happens in anaphase 1?

A

The homologous chromosomes are moved apart towards opposite poles of the cell. However, for now, sister chromatids remain attached to one another at the centromere.

52
Q

What happens in telophase 1?

A

The chromosomes arrive at opposite ends of the cell as the nuclear membrane is cleaved. A cleavage furrow forms in preparation for the cell to undergo cytokinesis.

53
Q

Why is crossing over important to genetic diversity?

A

Crossing over results in the formation of new recombinant chromatids each with its own unique combination of alleles. This adds to the genetic diversity of the resulting haploid daughter cell as the sister chromatids that they will inherit are no longer identical.

54
Q

Why is independent assortment important to genetic diversity?

A

Pairs of homologous chromosomes line up on opposite sides of the metaphase plate. The resulting combination of alleles in each daughter cell is randomised since what is inherited depends on which side of the metaphase plate each chromosome is positioned. The number of different combinations in humans is around 8 million.

55
Q

What is crossing over?

A

The exchanging of genetic material from one homologue to the other during prophase I. The homologous chromosomes will ‘cross over’ at a point called the chiasma, each swapping part of their DNA with the other.

56
Q

What happens in prophase 2?

A

The two cells are prepared for another division - the nuclear envelope begins to break down, the chromosomes condense, and the spindle fibres form in preparation to pull apart the sister chromatids of each chromosome.

57
Q

What happens in metaphase 2?

A

Each chromosome lines up along the metaphase plate of the cell, as microtubules from opposite poles of the cell prepare to pull the chromosomes apart.

58
Q

What happens in anaphase 2?

A

Sister chromatids are now separated and pulled towards opposite poles of the cell by microtubules, which are attached at each centromere.

59
Q

What happens in telophase 2?

A

With individual chromatids now at each pole of the cell, separate nuclear membranes begin to form around each set as the chromosomes begin to decondense and unravel.

60
Q

How much genetic information is in a gamete

A

Gametes contain half the genetic information of the germline cell and are each genetically unique from one another. Meiosis increases the genetic diversity present in resulting gamete cells through two processes:
* crossing over in prophase I – which exchanges genetic material between chromosomes and results in recombinant chromatids.
* independent assortment during metaphase I – which allows homologous chromosomes to arrange randomly along the equator of the cell and results in the random splitting of chromosomes into different daughter cells.

61
Q

What does it mean to be homozygous?

A

having identical alleles for the same gene on homologous chromosomes

62
Q

What does it mean to be heterozygous?

A

having different alleles for the same gene on homologous chromosomes

63
Q

What is a dominant allele?

A

the variant of a gene that masks the effect of a recessive allele of the same gene on a homologous chromosome

64
Q

What is a recessive allele?

A

the variant of a gene that is masked by a dominant allele on a homologous chromosome

65
Q

What is complete dominance?

A

when a dominant allele is fully expressed in a phenotype and masks the expression of a recessive allele. Although a dominant allele may mask the expression of a recessive allele, a person who is heterozygous at a specific gene locus is still a carrier, meaning they are able to pass on the recessive allele to their offspring despite not displaying the trait.

66
Q

What is a carrier?

A

an organism that has inherited a copy of a recessive allele for a genetic trait but does not display the trait due to it being masked by the presence of a dominant allele

67
Q

What is a genotype?

A

the genetic composition of an organism at one particular gene locus, as represented using letter symbols

68
Q

When does co-dominance occur?

A

when both alleles from the genotype are fully expressed in the phenotype of a heterozygote. That is, both alleles can be thought of as dominant and neither allele can mask the expression of the other allele.

69
Q

What is incomplete dominance?

A

a pattern of dominance where neither allele from the genotype of a heterozygous individual is dominant and both are expressed in an intermediate phenotype

70
Q

When does incomplete dominance occur?

A

when neither allele from the genotype is fully expressed in the phenotype of a heterozygote, and the resulting observable trait is a ‘blending’ of both alleles.

71
Q

What are sex-linked genes?

A

genes that are located on a sex chromosome
represented differently to autosomal traits, and are written using superscript notation and their sex chromosome – e.g. XAY.

72
Q

What are X-linked traits?

A

a trait controlled by a gene that is located on the X chromosome

73
Q

What are Y-linked traits?

A

a trait controlled by a gene that is located on the Y chromosome

74
Q

What are sex-linked genes?

A

genes present on either the X or Y chromosomes. However, the X chromosome is much longer than the Y chromosome, containing as many as 4 000 more genes. Therefore, when thinking about sex-linked inheritance, we are usually referring more specifically to X-linked traits, as these are far more common. Y-linked traits also exist, but are quite rare and only show up in males.

75
Q

Who are X-linked traits more likely to be expressed in?

A

X-linked traits are also more likely to be expressed in males than they are in females. This is because each male only receives one copy of an X chromosome, which comes from their mother. Whatever allele a male receives on the inherited copy of their X chromosome is what is expressed in their phenotype, regardless of whether that allele is dominant or recessive. There is no corresponding allele on the Y chromosome to cancel out the effects of the allele on the X chromosome. This means that if the allele is faulty and causes a condition, then that male has a 100% chance of showing that condition.

76
Q

Can males pass X-linked traits to their sons?

A

males with X-linked traits or conditions are unable to pass the trait on to their sons. This is because if a male has a son, that son must receive their Y chromosome from their father. Affected males can only pass on the abnormal X-linked gene to their daughters

77
Q

what is DNA methylation?

A

A chemical reaction in the body in which a small molecule called a methyl group gets added to DNA, proteins, or other molecules. The addition of methyl groups can affect how some molecules act in the body. Silences some genes

78
Q

What is epigenetics?

A

How lifestyle affects ones genome

79
Q
A

Biology (8 decks)

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