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Inherited Change Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Homologous pair of chromosomes

A

A pair of chromosomes in a diploid cell that have the same structure as each other, with the same genes (but not necessarily the same alleles) at the same loci, the pair forms a bivalent a during the first decision of meiosis

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2
Q

Haploid cell

A

A cell with only contains one set of chromosomes (n)

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3
Q

Diploid cells

A

A cell which contains two sets of chromosomes (2n)

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4
Q

The need for meiosis prior to fertilisation

A

Meiosis occurs before fertilisation, this is where the number of chromosomes half’s. So the gametes only contain one set of chromosomes. If this did not happen then the number of chromosomes would double every generation. Gametes are haploid

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5
Q

What produces genetic variation in meiosis

A

Independent assortment of homologous chromosome and crossing over between the chromatids of homologous chromosomes

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6
Q

Meiosis 1 early prophase

A

Chromatin coils up

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7
Q

Meiosis 1 middle prophase

A

Homologous chromosomes pair up, this process is called synapsis. Each pair is a bivalent. Centrosomes move to opposite ends of the nucleus

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8
Q

Meiosis 1 late prophase

A

Nuclear envelope breaks down, crossing over of chromatids may occur. A spindle forms

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9
Q

Bivalent crossing over

A

Chromatids break and reconnect to another chromatid, a chiasma is the point where the crossing over occurs

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10
Q

Meiosis 1 metaphase

A

Bivalent line up across equator of spindle, attached by centromeres

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11
Q

Meiosis 1 anaphase

A

Whole chromosomes move towards opposite ends of the spindle, centromeres first, it is pulled by microtubules but they don’t separate

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12
Q

Meiosis 1 telophase

A

Nuclear envelope re-forms, chromosomes have reached the pole of the spindle. Animal cells usually divide by cytokinesis, many plant cells go straight to meiosis 2 with no reforming of nuclear envelope

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13
Q

Meiosis 2 prophase

A

Centrosomes and centrioles replicate and move to opposite poles of the cells. The nuclear envelope breaks down

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14
Q

Meiosis 2 metaphase

A

Chromosomes line up separately across the equator of the spindle

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15
Q

Meiosis 2 anaphase

A

Centromeres divide and spindle microtubules pull the chromatids to opposite poles

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16
Q

Meiosis 2 telophase

A

Four haploid daughter cells are formed after cytokenesis. Nuclear envelope re-forms. Chromatids have reached the poles of the spindle

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17
Q

Spermatogenesis

A

The production of sperm, takes place within the tubules of the testes. Here diploid cells divide by mitosis to produce numerous diploid spermatogenia which grow to form diploid primary spermatocytes. They devide by meiosis to form two haploid secondary spermatocytes. The second division of meiosis then produces haploid spermatids which mature into spermatozoa or sperm

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18
Q

Oogenesis

A

The production of ovum, occurs in the ovaries where diploid cells divide by mitosis to produce oogonia. They begin to divide by meiosis, but stop when they reach prophase 1 to form diploid primary oocytes. This occurs when the child is an embryo. When the girl reaches puberty some of the primary oocytes proceed to the end of the meiotic cycle to form two haploid cells. This division is uneven with one cell getting most of the cytoplasm, this is the second oocyte, the other is little more then a nucleus and is the polar body. The polar body has no further role. Every month a secondary oocyte is released into the oviduct and is now called the ovum

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19
Q

Production of pollen

A

In the anther, diploid pollen mother cells divide by meiosis to form four haploid cells. The nuclei of each hapoid cell divides by mitosis but the cell does not divide. The cell has two hapoid nuclei, it then matures into pollen grains. One of the haploid nuclei is called the tube nucleus, the other is the generative nucleus.

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20
Q

Production of embryo sac (female plant gamete)

A

In each ovule a large, diploid, spore mother cell develops. It then divides by meiosis to produce four haploid cells. All but one degenerates, the surviving haploid cell develops into an embryo sac. The embryo sac grows larger and its haploid nucleus divides by mitosis 3 times forming eight haploid nuclei. One of these becomes the female gamete

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21
Q

Gene

A

A length of DNA that codes for a particular protein or polypeptide

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22
Q

Locus

A

The position at which a particular gene is found on a particular chromosome, the same gene is always found at the same locus

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23
Q

Allele

A

A particular variety of a gene

24
Q

Dominant

A

A dominant allele is one whose effect on the phenotype of a heterozygote is identical to its effect in a homozygote

25
Q

Recessive

A

A recessive allele is one that is only expressed when no dominant allele is present

26
Q

Codominant

A

Both alleles have an effect on the phenotype of a heterozygous organism

27
Q

Linkage

A

The presence of two genes on the same chromosome so that they tend to be inherited together and do not assort independently

28
Q

Test cross

A

A genetic cross in which an organism showing a characteristic caused by a dominant allele is crossed with an organism that is homozygous recessive, the offspring can be a guide to whether the first organism is homozygous or heterozygous

29
Q

F1 generation

A

The offspring resulting from a cross between an organism with a homozygous dominant phenotype and one with a homozygous recessive genotype.

30
Q

Heterozygous

A

Having two different alleles of a gene

31
Q

F2 generation

A

The offspring resulting from a cross between two F1 (heterozygous) organisms

32
Q

How do you use test crosses to solve problems

A

It is not possible to tell the genotype of an organism showing a dominant characteristic just by looking at it. It may have the genotype AA or Aa. To find this out you cross it with a homozygous recessive organism. From the characteristics of the offspring you can tell the genotype of the parent plant. If any of the recessive trait is shown it must be Aa.

33
Q

Multiple alleles

A

Lots of genes have more then two alleles, for example in the genes for human blood groups. The four blood groups A, B, AB and O are all determined by a single gene. The alleles are I^a, I^b and I^o. As a diploid cell can only carry two alleles, two out of the three will be in one persons cells.

34
Q

Autosomes

A

The chromosomes which are not sex chromosomes

35
Q

Sex linkage

A

Some genes are on the X or Y chromosomes. As men are XY and women are XX this affect the genes which are inherited. A sex-linked gene is one that is found on the X chromosome not matched by the Y chromosome. Sex-lined genes are represented as XhXH or XhY. If it is a recessive gene on the X chromosome which causes harm, the male has half a chance of displaying, whilst the women only has a quarter of a chance (could be dominant or heterozygous instead).

36
Q

Dihybrid crosses

A

These look at the inheritance of two genes together at once, they are not linked. For example, AaDd, the gametes would be AD, Ad, aD and ad. Instead of four different squares in the cross there would be 16 (4x4). A 9:3:3:1 ratio is typical for two heterozygote individuals

37
Q

Interaction between loci

A

When different loci interact to affect one phenotypic character. For example I/i and C/c, individuals carrying the dominant allele “I” will have white feathers even if they carry the dominant allele C for coloured feathers. So only iiCc or iiCC will result in coloured birds. This is demonstrates with the same table which is used in sex-linkage

38
Q

Autosomal linkage

A

When two or more gene loci are on the same chromosome they do not assort independently in meiosis as they would if they were on different chromosomes, they are linked. The genotype may be (EA)(Ea) and the gametes are (EA) and (Ea)

39
Q

Crossing over affect on phenotype

A

Gene loci can be exchanged between maternal and paternal chromatids during meiosis. Recombinant organisms can be produced, which results from the crossing over and recombining. These would not be predicted in the genetic crosses

40
Q

The crossing over value

A

The percentage of offspring which belong to the recombinant classes. This is a measure of the distance between two gene loci. The smaller the value the closer they are.

41
Q

Chi squared test

A

This test allows us to compare our observed results with our expected results and decide if there is a significant difference

42
Q

How to work at chi-squared test

A

You work out the expected results by doing a genetic test.
E= expected value
O= observed value

X= (O-E)^2
————-
E

43
Q

Mutations

A

A gene mutations change in the structure of a DNA molecule to produce a different allele of a gene

44
Q

Base substitution

A

Where one base takes the place of another for example GAG to GTG

45
Q

Base addition

A

Where one or more extra bases are added to the sequence

46
Q

Base deletion

A

Where one or more bases are lost from the sequence

47
Q

How do the different types of gene mutation affect the phenotype

A

Base addition or deletion usually have a significant change on the function of the polypeptide because they alter every set of three bases that follow them in the DNA molecule. Base substitution may have no effect at all as many amino acids have more then one triplet code, so even if a base is changed the same amino acid is coded for

48
Q

Sickle cell anaemia (inherited change)

A

The gene that codes for the beta globin polypeptide is different between people who have the Hb^A allele and the Hb^S allele which causes sickle cell anaemia. In the Hb^S allele the base sequence CTT is replaced by CAT and val is produced instead of Glu.

49
Q

Haemophilia

A

The gene that codes for a protein needed in blood clotting is called factor VIII and is found on the X chromosome. The dominant allele causes the normal allele and the recessive allele causes haemophilia. The chromosomes XhY causes haemophilia. Women don’t get it as XhXh causes a miscarriage

50
Q

Albinism characteristics

A

Melanin is missing form eyes, skin and hair. Results in pale skin and hair with red pupils

51
Q

Sickle cell anaemia characteristics

A

The unusual beta-globin polypeptide makes the haemoglobin molecule less soluble. The red blood cells are now in a sickle shape meaning they can carry less oxygen, they get stuck in capillaries stopping other cells from passing through

52
Q

How is albinism caused

A

The mutation is autosomal recessive and individuals that are homozygous recessive have albinism. A mutation in the gene for the enzyme tyrosinase causes it’s absence. Melanin can not be produced as tyrosine can it be converted into DOPA and dopaquinone as there is no enzyme to catalyse the reaction

53
Q

Huntington’s disease characteristics

A

A neurological disease which results in involuntary movement and progressive mental deterioration, brain cells are lost

54
Q

How is Huntington’s disease caused

A

A mutation which is inherited on the dominant allele. The mutation is on a gene on chromosome 4 which codes for the protein Huntington’s. People who have HD have a larger number of repeats of the CAG triplet (called a stutter), in normal people there are only a small number of repeats

55
Q

What to include in a genetic diagram

A

Say function of allele, ie tall or diseases. When stating the phenotypes in a sex linked diagram include the gender of offspring. For sex linked diagrams the allele should be written next the the sex chromosome as it where the square of it.

Biology (21 decks)

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