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HSC BIOLOGY > BP S3 > Flashcards

BP S3 Flashcards

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1
Q

What did Boveri do?

A

sea urchins; deduced that a complete set of chromosomes is needed for normal development, and that inheritance factors are found on chromosomes (chromosomes are the carriers of heredity)

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2
Q

Walter Sutton?

A

studied grasshoppers; formed the basis of the chromosome theory of inheritance. Found that chromosomes occur in distinct pairs and that chromosomes were the carriers of heredity units

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3
Q

chemical composition of chromosome

A

60% protein 40% DNA- DNA is coiled tightly around a protein core.

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4
Q

Structure of DNA

A

double stranded helic made up of sub-units (nucleotides).
each nucleotide is made up of a phosphate, sugar and nitrogenous base. (a-t, g-c)
A single stand of DNA is made up of a chain of nucleotides where the phosphate and the sugar are the backbone of the strand

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5
Q

stages of meiosis (creation of gametes and inheritance of genes)

A

chromosomes duplicate- single stranded chromosomes become double stranded linked by centromere
First meiotic division - homologous chromosomes separate.
second division, chromatids of chromosome separate and form 4 gametes

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6
Q

random segregation

A

during meiosis genes on different chromosomes sort independently. They can line up in the middle of cells in many different ways; producing many different gene combinations
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7
Q

crossing over

A

crossing over of genetic material results in the exchange of genes between chromosome pairs. the combinations will vary promoting variation

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8
Q

random fertilisation

A

two different gametes randomly fuse during mating. many different combinations are possible and this causes variation.

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9
Q

co dominance

A

both alleles are expressed - eg roan cattle both white and red hairs.

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10
Q

incomplete dominance

A

blending occurs- eg snapdragon flower - red+white gene= pink

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11
Q

sex linked

A

characteristics determined by sex chromosomes.

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12
Q

Morgan

A

studied the breeding of the fruit fly, discovering that white eye colour is sex linked.

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13
Q

DNA replication significance

A

significance of the ability of the DNA to replicate itself exactly is that identical copies of genes can be made and a complete set of genes can be passed on.

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14
Q

Who was Boveri?

A

A German Biologist, that in 1902 carried out experiments with sea urchins to show that a complete set of chromosomes is necessary for normal development of an organism.

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15
Q

Who was Sutton?

A

An american scientist who studied chromosomes in the testis of a grass hopper in 1902. His observations provided evidence that chromosomes could carry Mendel’s factors.

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16
Q

What did Sutton’s data show?

A
  • chromosomes are carriers of hereditary units and that units are transmitted with the chromosomes
  • chromosomes occur as homologous pairs
  • as a result of meiosis, every gamete receives only one chromosome of a pair
  • Chromosomes keep their individuality through out cell division
  • The distribution of the members of each homologous pair is independent of that of each pair.
  • since hereditary factors are more numerous than chromosomes, each chromosome has to carry many units.
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17
Q

Even though Sutton and Boveri worked separately, their work was known as…

A

The Sutton - Boveri Chromosome theory.

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18
Q

The chemical nature of a chromosomes?

A

They are made of DNA (deoxyribonucleic acid) and wrapped up into proteins (histones). In comparison they are to a necklace, with the genes acting as the singular beads. The thread that holds them together is the protein.

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19
Q

What is a DNA nucleotide made up of?

A

A nitorgen base, a sugar and a phosphate.

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20
Q

Name the four DNA nitrogen bases.

A

Thymine, Adenine, Guanine and Cytosine

they pair: AT and CG

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21
Q

Meiosis is a cell division that

A

produces sex cells and halves the number of chromosomes.

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22
Q

Daughter cells are also?

A

Sex cells.

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23
Q

What is the behaviour of chromosomes during meiosis

A
  • different pairs of homologous chromosomes behave independently of each other and each pair segregates randomly to the daughter cells
  • gene pairs on different chromosomes sort themselves in the same manner as the chromosome pairs

Since the chromosome pairs carry different genes, the sex cells produced by meiosis are almost always genetically different.

24
Q

Three important things to know about chromosomes?

A
  1. Chromosomes are thread like structures in the nucleus of cell, they only become visible during cell division.
  2. Chromosomes have genes along their lengths.
  3. Chromosomes occur in pairs. chromosomes in a pair are called homologus. Homologus pairs correspond to each other by carrying allelic genes in corresponding locations.
25
Q

Before cell division each chromosome is?

A

duplicated.

26
Q

The chromatids in a double chromosome are?

A

identical

27
Q

Outline process of meiosis

A
  1. Begin with a diploid cell
  2. the chromosomes are first duplicated to form double chromosomes
  3. chromosomes line up in their homologus pairs
  4. homologous pairs have seperated and cell divides in two
  5. now cells divide again and seperate the chromatids.
  6. become haploid cells.
28
Q

What does haploid mean?

A

means half the chromosome number. noting that the chromosomes are no longer in pairs.

29
Q

gamete cells/haploid cells are?

A

not identical to each other nor to parent cell.

30
Q

How does sexual reproduction result in the variability of offspring in correlation to meiosis?

A
  1. Gametes are formed by a process called meiosis, sex reproduction involves the joining together of two sex cells (fertilisation) with one ovum and one sperm. this produces the first cell of the offspring.

which cells join together is a random process, new combinations of genes occur the produces genetic variation.

  1. During meiosis chromosome pairs sort themselves independently and randomly this is called random segregation, this produces genetic variation
  2. when genes from different characteristics are found on the same chromosome they are called linked genes. these genes will usually be inherited together. Exceptions to this linkage occurs when crossing over happens.

Crossing over is a swapping of chromatid parts of the homologous chromosomes in early meiosis. This = new combinations of genes which increases variation across the resulting gametes.

31
Q

Variation caused by reproduction summaries?

A

Meiosis creates variations in the way homologous chromosomes separate and in the process of crossing over further variation comes from combining genes from 2 parents.

32
Q

What are the sex chromosomes ?

A

girls = XX boys = XY

33
Q

What are two examples of a sex linked diseases?

A

Haemophillia, and red green colour blindness.

34
Q

Why did mendel’s experiments not show sex linkage?

A

Mendel was fortunate in his choice of factors as they all showed dominant/recessive characteristics. However, sex-linked genes and genes that are co-dominant do not display the phenotype ratioos predicted by Mendel’s laws.

35
Q

Red green colour blindness, is a sexlinked inheritance disease, explain it

A

An example of sex-linked inheritance is red-green colour blindness in humans. The gene is carried on the X chromosome and there is no corresponding gene on the Y chromosome. Therefore males need only one allele for colour blindness on the X chromosome while females require two. This results in many more males being colour blind than females because the father would have to be colour blind and the mother either colour blind or be a carrier for colour blindness. As you would expect the sex of offspring to be 50% male and 50% female the occurrence of colour blindness is higher in males than would be expected from a simple pair of dominant and recessive genes. Take the cross between a normal female XN XN and a colour-blind male X n Y.

36
Q

Human blood types is an example of?

A

Co dominance

37
Q

Elaborate on human blood type as being co dominant

A

Human blood types are another example of co-dominance. Human blood types give different results from Mendelian ratios. When a homozygous male with AA alleles crosses with a homozygous female with BB alleles then all of the offspring will be a different phenotype from the parents (group AB).

38
Q

What is Co dominance? and why does it screw with Mendel?

A

Co dominance does not produce simple Mendelian ratios. CD occurs when the effects of both alleles appear together in the heterozyg offspring

eg. blue andalusian fowls are the heterozyg offspring of a cross between a black fowl and a white fowl. the blue colour is a mosaic of blue and white feathers.

Both parents genotypes are seen in the offspring.

39
Q

In 1901 what was Morgan and his students experimenting on?

A

the breeding of a small fruit fly, and the crosses between red eyed and white eyed male and female flies.

They found that the outcomes could not be expressed using mendels scheme.

40
Q

What did morgan discover with his fruit flies?

A

All genes that are carried on the X chromosome are sex linked.

41
Q

Environment and gene expression?

A

the features that an organism has such as its size and shape are not only controlled by its genes but also by the environment in which it lives.

42
Q

In the environment what determines how well genes are expressed?

A

water, nutrients, sunlight, type of soil, presence of poisonous substances, and competition of other organisms.

43
Q

Example of environmental expression

A

Hydrangeas are plants that have different flower colour (pink or blue) depending on the pH of the soil they are grown in. In acid soils (less than pH 5) Hydrangeas are blue. In soils that have a pH greater than 7 Hydrangeas are pink. The pH has an effect on the availability of other ions in the soil and it is these ions that are responsible for the colour change.

44
Q

Outline the roles of Sutton and Boveri in identifying the importance of chromosomes

A

Two scientists are credited with the discovery of the role of chromosomes in 1902. They were the German scientist Theodor Boveri and the American microbiologist Walter Sutton.

Boveri worked on sea urchins and showed that their chromosomes were not all the same and that a full complement was required for the normal development of an organism.

Sutton worked on grasshoppers and showed that their chromosomes were distinct entities. He said even though they duplicate and divide they remain as a distinct structure. He associated the behaviour of chromosomes with Mendel’s work on the inheritance of factors and concluded that chromosomes were the carriers of hereditary units.

Together their work became known as the Sutton-Boveri chromosome hypothesis.

45
Q

Describe the chemical nature of chromosomes and genes

A

Chromosomes consist of 40% DNA and 60% protein (histone). Short lengths of DNA make up genes so genes have the same chemical composition as DNA. DNA is described in more detail in Part 4.

46
Q

Identify that DNA is a double-stranded molecule twisted into a helix with each strand, comprised of a sugar-phosphate backbone and attached bases, adenine (A), thymine (T), cytosine (C) and guanine (G), connected to a complementary strand by pairing the bases, A-T and G-C

A

In summary, DNA is a nucleic acid in the shape of a double helix. Each strand of the helix consists of four different nucleotides made up of deoxyribose sugar, a phosphate molecule and a nitrogen base. The helix is like a twisted ladder. The backbones of the structure, or the sides of the ladder, consist of the deoxyribose sugar and phosphate molecules. The bases form the rungs between the sides of deoxyribose sugar and phosphate molecules and are complementary (only pair with their matching base). Adenine pairs with thymine and guanine pairs with cytosine.

47
Q

Explain the relationship between the structure and behaviour of chromosomes during meiosis and the inheritance of genes

A

Chromosomes are made of DNA. Genes are coded within the DNA on the chromosomes. During division each chromosome (which therefore includes the genes) makes a complete copy of itself. The new chromosome is attached to the original chromosome by a centromere. In the initial division of meiosis the homologous chromosomes line up in matching pairs and one of each pair of homologous chromosomes moves into a new cell. Next the duplicated chromosomes separate to single strands resulting in four sex cells that are haploid, (ie contain half the chromosome number of the original cell).

The genes are located on the chromosomes. They are duplicated during the first stage of meiosis and are then randomly assorted depending on which chromosomes from each pair enters which new haploid cell during the first and second division.

48
Q

Explain the role of gamete formation and sexual reproduction in variability of offspring

A

Gamete formation results in the halving of the chromosome number (n) (diploid to haploid) and sexual reproduction results in combining gametes (haploid to diploid) to produce a new diploid organism (2n). The processes involved in forming this new organism result in variability of the offspring.

Gametes are formed during the process of meiosis. In meiosis there are two stages that lead to variability. These are:

  • random segregation of individual chromosomes with treir associated genes ie, different new combinations of the original maternal and paternal chromosomes and
  • the process of crossing over where the maternal and paternal chromosomes of each pairmay exchange segments of genes making new combinations of genes on the chromosomes.

In sexual reproduction each female or male cell produces 4 sex cells (gametes) from the process of meiosis. Each of these sex cells is haploid (has half the normal chromosome number) and has a random assortment of genes from the parent. The genes (Mendel’s alleles) are separated and the sex cells have a random assortment of dominant and recessive genes. More variability is introduced depending on which sex cells are successful in fertilisation. The resulting embryo has a completely different set of genes from either of the parents.

49
Q

Describe the work of Morgan that led to the identification of sex linkage

A

Thomas Morgan worked on the fruit fly Drosophila melanogaster. He looked at crosses between red- eyed and white-eyed flies and found that the results could not be accounted for by simple Mendelian crosses. He showed that some genes were sex-linked because they were located on the X chromosome.

50
Q

Explain the relationship between homozygous and heterozygous genotypes and the resulting phenotypes in examples of co-dominance

A

If an individual has two different alleles (heterozygous) for a characteristic, then often one will be dominant while the other is not expressed and is said to be recessive. In some cases however, both alleles are expressed in the phenotype and the two alleles are said to be co-dominant. In this case both alleles are labelled with upper case letters

An example of co-dominance is human blood groups. There are three alleles for blood type A, B and O. O blood type is recessive to both A and B but A and B are co-dominant and form a fourth blood type AB.

Another example of co-dominance is in coat colour of Shorthorn cattle. These animals have an allele for both red and white hair. As neither is dominant, cattle with both alleles have a mixture of red and white hairs scattered over their bodies and are called roan. Red cattle have the alleles RR while white cattle have WW. In the F1 (first) generation all of the offspring will be roan, RW

51
Q

Describe the inheritance of sex-linked genes, and genes that exhibit co-dominance and explain why these do not produce simple Mendelian ratios

A

Mendel was fortunate in his choice of factors as they all showed dominant/recessive characteristics. However, sex-linked genes and genes that are co-dominant do not display the phenotype ratioos predicted by Mendel’s laws.

An example of sex-linked inheritance is red-green colour blindness in humans. The gene is carried on the X chromosome and there is no corresponding gene on the Y chromosome. Therefore males need only one allele for colour blindness on the X chromosome while females require two. This results in many more males being colour blind than females because the father would have to be colour blind and the mother either colour blind or be a carrier for colour blindness. As you would expect the sex of offspring to be 50% male and 50% female the occurrence of colour blindness is higher in males than would be expected from a simple pair of dominant and recessive genes. Take the cross between a normal female XN XN and a colour-blind male X n Y.

Human blood types are another example of co-dominance. Human blood types give different results from Mendelian ratios. When a homozygous male with AA alleles crosses with a homozygous female with BB alleles then all of the offspring will be a different phenotype from the parents (group AB).

52
Q

Outline ways in which the environment may affect the expression of a gene in an individual

A

The appearance of an individual is not based solely on their genetic information. The environment of the organism also plays a part.
Hydrangeas are plants that have different flower colour (pink or blue) depending on the pH of the soil they are grown in. In acid soils (less than pH 5) Hydrangeas are blue. In soils that have a pH greater than 7 Hydrangeas are pink. The pH has an effect on the availability of other ions in the soil and it is these ions that are responsible for the colour change.
Burke’s Backyard (external website) Don Burke, Australia
Hydrangeas! Hydrangeas! (external website)Judith King, USA
Another example of the influence of the environment on the appearance is the height of plants. Genetically identical plants will grow to different heights if they are exposed to different growing conditions.

53
Q

You needed to preform a first hand investigation on the effect of the environment on a phenotype. Name an Aim.

A

“To investigate the effect of light intensity (environment) on length of stem (phenotype)”

54
Q

Name a method to the following aim “To investigate the effect of light intensity (environment) on length of stem (phenotype)”

A
  1. Soak chick peas in water for a day
  2. Place twenty seeds in petri dishes containing moist cotton wool and place in a dark cupboard with plenty of air circulation
  3. Repeat but place seeds in light, ensure other variables such as air circulation, humidity and temperature are the same.
  4. Measure stem after five days
  5. Calculate average stem length after five days
55
Q

Name the results to the practical that has the aim “To investigate the effect of light intensity (environment) on length of stem (phenotype)”

A

Stem length for peas grown in low levels of light is greater than those grown in strong light.

56
Q

What would you conclude from these results? “Stem length for peas grown in low levels of light is greater than those grown in strong light.”

A

Assuming that all seeds had similar genotype for stem length, it can be seen that the environment influences the expression of the genotype and the phenotypes (stem lengths) are different.

HSC BIOLOGY (21 decks)

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