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Biology Unit 4 > Inheritance (DONE) > Flashcards

Inheritance (DONE) Flashcards

1
Q

What are the definitions of the following terms:
- Gene
- Locus
- Allele

A
  • Strand of DNA on a chromosome that codes for a specific polypeptide
  • Specific position on a chromosome where a gene is located
  • Different forms of the same gene
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2
Q

What are the definitions of the following terms:
- Dominant
- Recessive
- Codominant

A
  • Allele will always be expressed in the phenotype when present in the genotype
  • Hidden when dominant allele is present/will only be expressed when it is homozygous
  • Alleles that are both dominant and equally expressed in the phenotype
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3
Q

What are the definitions of the following terms:
- Phenotype
- Genotype
- Homozygous
- Heterozygous

A
  • The characteristics of an organism
  • The genetic makeup of an organism
  • Both alleles for a gene are identical
  • Both alleles for a gene are different
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4
Q

What are the definitions of the following terms:
- F1
- F2
- Autosomes
- Sex Chromosomes

A
  • First filial generation: the offspring of the parents in a genetic cross
  • Second filial generation: the offspring of F1
  • Chromosomes that aren’t sex chromosomes
  • Chromosomes (X and Y) that determine the sex of an individual organism
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5
Q

What 3 things did Gregor Mendel propose from the monohybrid crosses?

A
  • Genetic characteristics are controlled by alleles
  • When two alleles responsible for a single characteristic in an individual, one is dominant while the other is recessive
  • During the formation of gametes the alleles separate randomly, so that each gamete receives one of the alleles in equal likelihood
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6
Q

What are the two of Mendel’s Laws?

A
  • 1st Law of Segregation
  • 2nd Law of Independent Assortment
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7
Q

What ratio will the phenotypes be in the dihybrid cross of two heterozygotes?

A

9:3:3:1

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8
Q

What is a Testcross used for?

A
  • To determine the unknown genotype of an individual with a dominant phenotype
  • Breeding the individual with an individual that expresses a recessive version of the same trait
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9
Q

What should always be included in your answer for a chi2 analysis?
(4 marks)

A
  • Null hypothesis: there is no significant difference between the observed and the expected values of each phenotype
  • State degrees of freedom used and null hypothesis
  • If Chi2 is less than critical value accept the null hypothesis
  • If Chi2 is more than critical value reject null hypothesis and state that there is a significant difference due to genes are linked on the same chromosome
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10
Q

What are the three ways that meiosis and fertilisation in variation?

A
  • Mixing the genotype of one parent with that of another increases variety of offspring
  • The random distribution and independent assortment of homologous chromosomes during metaphase 1 of meiosis 1.
  • Crossing over during chiasmata formation during prophase 1 of meiosis.
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11
Q

What is genetic/autosomal linkage?

A

When genes are on the same chromosome and more likely to stay together during meiosis.
All chromosomes apart from X and Y.

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12
Q

What is sex linkage?

A
  • When a gene is carried on a sex chromosome, so the characteristics is predominantly seen in one sex.
  • There are more genes on the X than on the Y.
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13
Q

What is haemophilia?

A
  • Sex linked disease
  • Gene on the X chromosome that codes for factor 8, a blood clotting protein, which is defective for haemophiliacs
  • Recessive allele causes disease
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14
Q

What is Duchenne Muscular Dystrophy?

A
  • Sex linked disease
  • Recessive allele causes disease
  • Progressive muscular degeneration and weakness in the arms and legs
  • Mutation in the gene which codes for a protein (dystrophin), which stabilises muscle fibre cell membrane
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15
Q

How is sex determined and what is common for sex linked recessive alleles?

A
  • XX females
  • XY males
  • Carried on the X chromosome
  • Only expressed in females if both X chromosomes carry the allele
  • Always expressed in males since the Y chromosome does not have a homologous locus for the gene
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16
Q

What is a mutation and what is it sped up by?

A
  • Change in the amount, arrangement or structure of the DNA of an organism
  • Induction by a mutagen (carcinogen) e.g. uv light, X-rays, polycyclic hydrocarbons (cigarettes)
17
Q

What does mutation contribute to and where do most mutations occur?

A
  • If advantageous, contributes to evolution of a species
  • During crossing over in prophase 1 and nondisjunction in anaphase 1 and 2 (chromosomes do not separate)
18
Q

What are the three types of mutation?

A

Substitution, Insertion and deletion

19
Q

What is gene (point) mutation? Give an example of gene mutation

A
  • Affect as single base in a gene/occurs at a single locus
  • Sickle cell anaemia
20
Q

What is a chromosome mutation and give the two different types of chromosome mutation.

A
  • A change in the number of chromosomes in an organism
  • Polyploidy have additional set of chromosomes (triploid 3n)
  • Additional chromosomes during anaphase 1 of meiosis/nondisjunction
21
Q

What is down’s syndrome?

A
  • During meiosis if the daughter cells do not contain an equal share of the chromosomes it is referred to as nondisjunction
  • If this happens with chromosome 21 the person has down’s syndrome
  • This is called trisomy 21
22
Q

What is a carcinogen?

A

Mutagen that causes mutation that will also cause cancer

23
Q

What is cancer caused by?

A

Mutations in the tumour suppressor genes of proto-oncogenes, which mutate to oncogenes

24
Q

What are proto-oncogenes?

A

They are normal and code for proteins which contribute to cell division

25
Q

What do oncogenes contribute to?

A

Excessive protein production/cellular division
Proteins are incorrect or are resistant to removal

26
Q

What are tumour suppressor genes and what does mutation to them cause?

A
  • Regulate mitosis and prevent cells dividing too quickly
  • A loss of function
27
Q

What is the function of the normal Gene P53 tumour suppressor compared with the mutated p53?
(3 comparisons)

A

Normal:
- Activates repair of damaged DNA
- Holds cell in G1 until damage repaired
- Initiated apoptosis (cell dies)
Mutated:
- No DNA repair
- Cell with damaged DNA enters S phase and DNA is replicated
- Mutant cells survive and undergo mitosis

28
Q

What is epigenetics?
(2 marks)

A

The control of gene expression by modifying DNA or histones without changing nucleotide sequence.
The environment can affect the expression of genes and how they’re transcribed

29
Q

What are the two epigenetic modifications?

A
  • DNA methylation
    addition of methyl groups prevents those bases being recognised and reduces the ability of that gene to be expressed
  • Histone modification
    If the histone coils more tightly they can prevent gene expression. If the histone coils loosely they can increase gene expression

Biology Unit 4 (7 decks)

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