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A2 biology > Genetic inheritance > Flashcards

Genetic inheritance Flashcards

1
Q

Explain the terms haploid and diploid

A

haploid: cells that contain a single set of chromosomes
diploid: cell that contain two sets of chromosomes

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2
Q

distinguish between gene and allele
(pp)

A

gene: sequence of DNA which codes for protein
allele: different form of
gene.
occupying same
locus

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3
Q

locus

A

position a particular gene is found on a particular chromosome
*the same gene is always found at the same locus

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4
Q

meaning of recessive
(pp)

A

allele which does not have an effect on heterozygote

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5
Q

explain the term “homologous chromosomes”
(pp)

A

a pair of chromosomes in a diploid cell that have the same structure and genes at the same loci, and pair during the meiotic division to form a bivalent

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6
Q

explain what is meant by “dominant allele”?
(pp)

A

dominant: allele which always expresses itself in phenotype when present
allele: different form of gene

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7
Q

explain what is meant by sex linked gene?
(pp)

A

sex linked: allele present on one sex chromosome
gene: sequence of DNA which codes for protein

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8
Q

explain what is meant by heterozygous genotype?
(pp)

A

heterozygous: two different alleles of a gene, produces gametes of different genotypes
genotype: alleles present in an organism

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9
Q

meaning of heterozygote linkage
(pp)

A

autosomal: non sex chromosome
linkage: genes on the same chromosome

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10
Q

explain why there is a need for reduction division (meiosis)?

A

1) number of chromosomes would double every generation
2) introduces genetic variation

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11
Q

prophase I

A

1) condensation of chromosomes
2) mitotic spindle begins to form
3) centrosomes move to opposite poles
4) synapsis occur- homologous chromosomes pair up to form bivalents
5) nuclear envelope and nucleolus disappears
6) crossing over of non sister chromatids at chiasmata occurs

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12
Q

metaphase 1:

A

1)bivalents line up at the equator of spindle attached by centromere
2)independent assortment- homologous chromosomes align at the equator independently of each other causing different combinations of paternal chromosomes

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13
Q

anaphase 1:

A

homologous chromosomes move to opposite poles of the cell, centromeres first, pulled by microtubules

*sister chromatids stay together

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14
Q

telophase 1

A

1) nucleolus reforms
2)nuclear envelope reform 3) cytokinesis occurs- cell divides
number of chromosomes in each daughter cell are now halved. 2 haploid cells are formed

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15
Q

brief interphase between meiosis I and meiosis II

A

1) growth
2) synthesis of protein and other substances
3) DNA replication DOES NOT occur
plants go straight into meiosis II

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16
Q

Prophase II

A

1) nuclear envelope and nucleolus breaks down
2) centrosomes and centrioles replicate and move to opposite poles of the cell
3) condensation of chromatin

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17
Q

metaphase II

A

1) chromosomes line up across the equator of the spindle
2) independent assortment of sister chromatids occurs

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18
Q

anaphase II

A

1) centromeres divide
2) chromatids separate
3) spindle microtubules pull the chromatids to opposite poles

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19
Q

telophase II

A

1) the spindle fibres break down
2) chromosomes decondense
3) nucleolus reforms
4) cytokinesis
nuclear membrane forms around each set of chromosomes forming 4 haploid cells

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20
Q

Describe the behaviour of chromosomes during the main stages of meiosis I in animal cells? /4
(pp)

A

prophase 1:
-chromosomes condense
-homologous
chromosomes pair up
known as synapsis
-crossing over occurs
between chromatids of
non sister chromosomes
and they exchange
genetic material
metaphase 1:
-bivalents align at the
equator
-independent
assortment of
chromosomes
anaphase 1:
-one of each pair of
chromosomes moves to
opposite poles
telophase 1:
-chromosomes reach
the opposite poles
and chromosomes
decondense

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21
Q

describe how crossing over causes variation?
(pp)

A
  • crossing over is the exchange of genetic material between homologous chromosomes
  • linkage groups broken
  • new combinations of alleles produced when sister chromatids separate
  • leads to genetic variation
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22
Q

explain how meiosis can result in genetic variation amongst offspring?
(pp)

A

1) crossing over: synapsis occurs in prophase I. during synapsis homologous chromosomes pair up. these pairs are known as bivalents.
crossing over occurs in prophase I. during crossing over, chromatids of non sister chromosomes cross over at chiasmata and exchange their genetic material. this causes linkage groups to be broken, new combinations of alleles are formed when sister chromatids separate

2) independent assortment- it occurs in metaphase I and II and causes genetic variation. during independent assortment, homologous chromosomes align at the equator independently of each other causing different combinations of paternal chromosomes

3)random mating- random combination of chromosomes generated leading to genetic variation

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23
Q

explain why two genes assort independently? /3
(pp)

A
  • genes are on separate chromosomes
  • each pair of homologous chromosomes align itself separately
  • at equator in metaphase I of meiosis
  • paternal combinations of alleles is not preserved
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24
Q

when does independent assortment not happen?

A

independent assortment will not occur if two genes are located on the same chromosome (linked genes)

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25
Q

what is meant by codominant?

A

alleles that both have an effect on the phenotype of a heterozygous organism

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26
Q

what is meant by linkage?

A

the presence of 2 genes on the same chromosome so that they tend to be inherited together and do not assort independently

27
Q

F1

A

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

28
Q

F2

A

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

29
Q

distinguish between phenotype and genotype?
(pp)

A
  • phenotype: it is the feature which results from interaction between genotype and environment. The environment may alter the appearance of the organism
  • genotype: it is the characteristics inherited onto the offspring. genotype is not affected by the environment
30
Q

meaning of heterozygous and homozygous?

A
  • heterozygous: having 2 different alleles of a particular gene
  • homozygous: having 2 identical alleles of a particular gene
31
Q

monohybrid inheritance

A

inheritance of 1 gene

32
Q

dihybrid inheritance

A

the inheritance of two characteristics which are controlled by different genes, at once

33
Q

autosomal linkage

A

gene loci present on the same autosome that are often inherited together and do not assort independently

34
Q

why are males at greater risk of sex linked disorders caused by recessive alleles?

A

females: XX
males: XY

The X chromosome is much larger than the Y chromosome, so for many of the genes on X chromosome there is no homologue on the Y chromosome.
Therefore, recessive alleles on X chromosome will appear more frequently in the phenotype in males, because they only have one copy of the gene

35
Q

explain how gene mutation can affect the gene product?

A

1) silent mutation: a change in one base does not affect the amino acid the codon codes for. This is due to the degenerate nature of the genetic code

2) nonsense mutation: the new base creates a STOP codon, which means the protein is not fully produced

3) missense mutation: the new codon codes for a different amino acid. it may change the shape of the protein produced

4) frameshift: deletions or insertions shift the sequence, so every codon downstream is read differently, resulting in a different amino acid and potentially a completely different protein

36
Q

describe how albinism can result as a result of mutation?

A

one form of albinism is caused by the mutation of the tyrosinase (TYR) gene.
such mutations alter the tyrosinase enzyme which is responsible for the production of melanin; an inactive or absent enzyme results in albinism

37
Q

Explain how a mutation in the TYR gene can result in albinism? /2
(pp)

A
  • caused due to base substitution
  • so change in primary structure of protein so change in active site
  • no tyrosinase produced
    -tyrosine not converted to DOPA
  • melanin not produced
38
Q

describe how the expression of the TYR gene leads to the production of melanin? /3
(pp)

A
  • TYR gene codes for tyrosinase
  • tyrosinase converts tyrosine to DOPA
  • and DOPA is converted to dopaquinone
  • dopaquinone is converted to melanin
39
Q

Describe the phenotype of a person with albinism?
(pp)

A
  • pale skin
  • red eyes
  • poor vision
40
Q

mutation that causes sickle cell anaemia

A

a base substitution occurs in the gene coding for amino acid sequence in β-globin
CTT (glumatic acid) → CAT (valine)

Hbᴬ → Hbˢ

41
Q

Outline the phenotypic effects of having abnormal haemoglobin in person with sickle cell anaemia
(pp)

A

1) haemoglobin is less soluble
2) haemoglobin molecule forms long fibres
3) red blood cells becomes sickle shaped
4) blood poor at transporting oxygen
5) less oxygen getting to tissues
6) RBC may get stuck in vessels
7) fatigue

42
Q

describe how a mutation can lead to haemophilia?

A

The F8 gene which codes for factor VII (involved in blood clotting) is mutated in haemophilia.
this gene is found on the X chromosome, so this is a sex-linked disorder caused by a recessive allele

43
Q

why a man with haemophilia cannot pass it to his male offspring? /3
(pp)

A
  • males have only 1 X chromosome
  • man passes Y chromosome to his son and X chromosome to his daughter
  • woman passes X chromosome to son
    haemophilia allele is present on X chromosome
44
Q

explain how Huntingtin’s disease can arise from a mutation?

A

1) mutation is inherited as a dominant allele
2) the mutation is an unstable segment in a gene on chromosome 4 coding for the protein huntingtin
3) in people who do not have HD, the segment is made up of a small number of repeats of the triplet of bases CAG, people with HD have a large number of repeats called ‘stutters’
4) more stutters → earlier age of onset
5) age of onset is usually middle-age

45
Q

effects of Huntington’s disease

A

1) neurological disorder resulting in involuntary movements (chorea) and progressive mental deterioration
2) brain cells are lost
3) the ventricles of the brain become larger

46
Q

structural genes

A

genes that code for proteins needed by a cell;

they may form a part of the cellular structure or have different roles such as behaving as an enzyme

47
Q

regulatory genes

A

genes that code for proteins that regulate the expression of other genes;

by making proteins such as repressors that inhibit operator genes or control the transcription of another gene

48
Q

what is the difference between structural genes and regulatory genes?

A

a regulatory enzyme controls the expression of other genes
a structural enzyme is the one that codes for a protein or RNA that does not regulate the expression of other genes

49
Q

repressor enzyme

A

The synthesis of a repressible enzyme can be prevented by binding a repressor protein to a specific site, called an operator, on a bacterium’s DNA.

50
Q

inducible enzyme

A

The synthesis of an inducible enzyme occurs only when its substrate is present. Transcription of the gene occurs as a result of the inducer (the enzyme’s substrate) interacting with the protein produced by the regulatory gene.

51
Q

What is the difference between a repressible protein and inducible protein?

A

The synthesis of a repressible protein is only stopped when a repressor protein is present
The synthesis of an inducible protein is only started when a substrate is added

52
Q

using named examples; describe the differences between structural and regulatory genes and the differences between repressible and inducible enzymes? /9
(pp)

A

-structural genes:
. coded for non
regulatory proteins
. examples of structural
genes are: Lac Z, Lac Y,
Lac A
. proteins associated
with rRNA, tRNA
. proteins such as
enzymes

  • regulatory genes:
    . codes for regulatory
    protein
    . example; genes
    coding for repressor
    proteins, Lac I, PIF
    . switches genes on and
    off, controls gene
    expression and
    transcription
  • repressible enzymes:
    . produces
    continuously
    . synthesis can be
    prevented by
    binding of repressor
    protein to specific
    site/ promoter
  • inducible enzymes:
    . synthesis only occurs
    when substrate is
    present
    . transcription of gene
    only occurs when
    substrate/ inducer
    binds to transcription
    factor
    . example; lactose permease, B-galactosidase
53
Q

what type of operon is a lac operon?

A

an inducible operon

54
Q

Structure of lac operon

A

-consists of a cluster of three structural genes (lacZ, lacY, lacA) and a length of DNA including operator and promoter regions which control lactose metabolism in E. coli
- close to the promoter, but not actually part of the operon, is its regulatory gene
- genes within an operon will always be expressed together or not at all because they’re under the control of a single promoter

55
Q

Lac Y

A

encodes lactose permease (allows lactose to enter cell)

56
Q

Lac A

A

encodes transacetylase (with unknown function)

57
Q

Lac Z

A

encodes β-galactosidase (hydrolyses lactose to glucose and galactose)

58
Q

sequence of events when lactose is present in the medium in which the bacterium is growing

A

1) lactose is taken up by the bacterium
2) lactose binds to the repressor protein, distorting its
shape and preventing it from binding to DNA at the
operator site
3) transcription is no longer inhibited and messenger
RNA is produced from the three structural genes. The genes have been switched on and are transcribed together

59
Q

sequence of events when there is no lactose in the medium in which the bacterium is growing

A

1) the regulatory gene codes for a protein called a repressor
2) the repressor binds to the operator region, close to the gene for β-galactosidase
3) in the presence of bound repressor at the operator, RNA polymerase cannot bind to DNA at the promoter region
4) no transcription of the three structural genes can take place

60
Q

why the lac operon mechanism is useful

A

1) This mechanism allows the bacterium to produce β-galactosidase, permease and transacetylase only when lactose is available in the surrounding medium and to produce them in equal amounts
2) avoids the waste of energy and materials in producing enzymes for taking up and hydrolysing a sugar that the bacterium may never meet

61
Q

Explain the role of the Lac I gene in the regulation of the Lac Operon?
(pp)

A
  • Lac I is always expressed. it controls gene expression
  • Lac I gene codes for repressor protein
  • repressor binds to the operator and prevents gene expression
  • Lactose binds to the repressor
  • so repressor cannot bind to the operator
62
Q

Name the molecules that regulate gene expression in eukaryotes

A

Transcription factor

63
Q

Explain the function of transcription factors in gene expression in eukaryotes
(pp)

A

1) form part of the protein complex that binds to the promoter region of the gene
2) TF bind to DNA so RNA polymerase can bind to promoter so transcription begins
3) activate genes in correct order/time
4) determination of sex in animals
5) allow responses to environmental stimuli
6) regulate cell cycle, growth and apoptosis
7) give hormones their effect

A2 biology (9 decks)

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